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EDIT: Revisited in Feb 2017 - some more tips, corrections, clarifications, and simplifications!

Who are you?

I'm not a professional mechanic. I'm what many would call a bedroom mechanic. I work in IT and am interested in cars. I'm a long time lurker and recently bought my first MX5 (2001 Mk2.5 JDM RS 6 Speed) a couple of months ago. I also have an Evo 7. For perspective, examples of jobs I've done previously on my cars is far from extensive and amazing - brakes (fluid, discs, pads), wheel bearings, coilover fitment, and the usual servicing jobs such as plugs, leads, filters, oils etc. The most difficult/extensive job I've done is a clutch change on the Evo. I've never done a cambelt before and with it due on the MX5, and it being a non-interference engine - what better time to learn? The ease of access on this car is an obvious bonus.

Why another cambelt guide?

I know there are several guides out there but there isn't one specifically for the Mk2.5 VVT BP-Z3 Engine, and whereas the differences are relatively subtle, and you can piecemeal a guide together from using various sources, I thought it would be a good idea to write one - and a laymans one at that. This is also an exercise to help me understand what I've learned along the way.

What car was this done on?

As above, this was done on a 2001 1.8 Mk2.5 JDM RS 6 Speed. Any differences as a result from revisions, different models or it being Japanese are out of my control - sorry!

Own risk

Obviously by following this guide, you do so at your own risks and I'm not responsible for any issues you may have as a result. It's also a V1.0 guide so there is bound to be plenty of amendments, mistakes and omissions. I'll do my best to address these - please feel free to correct me.

This guide is LONG

It's long. Like really long. This is a TLDR guide - It's wordy and deliberately so. It is written with the mechanical beginner in mind who has never done a cambelt and thus elaborates extensively on points which I may not have understood the first time around. I'd advise any beginners not to be dissuaded from attempting this job. It's really not too bad as long as you take your time and are dilligent about it.

Issues with tensioning

Another reason for doing this, is that I had to re-tension my cambelt twice due to whining, and others have had problems, and so I thought again that it would be a good opportunity to describe the process in granular details to prevent others from having to do the same.

How long does this take?

Obviously depends on you and your background, and how many of the optional tasks you decide to do. Swapping the cambelt and pulleys is actually the quickest part of the job once you know how, doing the oil seals and water pump extends the job significantly. Doing everything took me a weekend - both days, 9-5. However, I like to understand exactly what I'm doing and so I take things very slow. I'm confident that if just doing the cambelt and pulleys -I could now easily do this in 2-3 hours at a comfortable pace.
Bottom line, it shouldn't take more than a weekend if you take your time, but I never recommend working to deadlines when it comes to cars (I.e. "I need the car working by time/date X or I'm screwed").

What knowledge do I need to do this job?

You need to be interested, motivated and reasonably mechanically competent. I'd advise reading up on the combustion cycle of a four stroke engine at a minimum too.

Read the whole guide

As above, if you are new to this, read the whole thing before you attempt the job. Don't be put off by how much I've waffled on.

Why should I do this job?

Well you don't have to obviously. I did it because I want to run the MX5 on the cheap (cheap does not mean without care) and learn as much as possible on the journey.


................are due to Westy for support and sanity checking. Anything wrong or idiotic here is nothing to do with him unless explicitly stated otherwise ;-)

Parts you'll need/want:

Prices correct at time of when I did the job (Feb 2013)

MANDATORY: Timing belt kit including timing belt, Tensioner Pulley, Idler Pulley, Cam Cover Gasket, Tensioner Spring: £70.96
Timing Belt - IL M/S £14.95, A/M £16.34
Tensioner - OEM £39.46, A/M £24.60
Spring - A/M £3.17
Idler - A/M £16.76
OPTIONAL BUT HIGHLY RECOMMENDED: Cam Cover Gasket - OEM £22.61 - Get an OEM Mazda one - (This is a Mk2.5 specific gasket because a bracket on the VVT engine cam cover means that the plug well sections of the gasket are seperated in one place - make sure you get the correct one!) - (2017 update - Checked and my gasket is a mess - cracked and brittle - I'd say change this if you don't know if it has been changed)

OPTIONAL BUT RECOMMENDED: Camshaft sprocket locking tool:
OPTIONAL BUT RECOMMENDED: Power Steering Belt £6.77 (You can use your old one, but they are only 7 quid)
OPTIONAL BUT RECOMMENDED: Alternator Belt - £6.67(You can use your old one, but as above, they are only 7 quid)
OPTIONAL BUT RECOMMENDED: Water Pump - OEM £54.62 / A/M £44.11 (It's up to you, but you'll be annoyed if it breaks or leaks a month after you do the belt. Even if you decide to inspect the old one before buying one - you'll most likely have to defer the whole job if you happen to need a new one)
OPTIONAL: Water pump O ring (I didn't change this as I forgot to order this)
OPTIONAL BUT RECOMMENDED: Crankshaft Pulley bolt - £9.05 (My old one was pretty burred after various use)
OPTIONAL BUT RECOMMENDED: Woodruff Key - £3.79 (Recommended as you may mangle the old one trying to get it out - looking at various different pictures, I think this may be specific to the VVT engine - make sure you specify this to your parts supplier)
OPTIONAL:Camshaft oil seal: OEM £7.01 (Tough one this. My 12 year old one looked in great shape but similar to the water pump, you'll be annoyed if one of yours is leaking and you didn't order one!)
OPTIONAL: VVT camshaft oil seal- £10.86 (This is a Mk2.5 specific part as the VVT mechanism means this part is bigger than on previous engines - get the right one.)
OPTIONAL (BUT HIGHLY RECOMMENDED): Crankshaft Oil Seals: £5.51 - good idea to buy a couple in case something goes wrong (Same comment as the camshaft oil seal - mine was leaking however so I'm glad I bought this in advance) - (2017 Update - I don't rate these seals much at all and I recommend you replace it)
Crank nut locking tool - Not sure if there is one available that fits the MK2.5 due to the recessed bolts in the crank pulley. I used a different method (detailed below).
OPTIONAL BUT RECOMMENDED: Thermostat (Mazda) (You're in there, you've drained the coolant, you may as well change this. Buy Mazda as there is plenty of complaints at aftermarket thermostats)


OPTIONAL: 6 litres of coolant -£6.64 per litre (You can re-use your coolant, but I changed mine)
RECOMMENDED: OEM Service Kit - OEM Filter, Sump Plug Washer, Air filter, Spark plugs. 5 litres of oil - £51.23 (I'd say the oil and oil filter are mandatory. I didnt change air or sparks as mine are newish. Sump plug is optional, but i'd buy a washer at the least)

Required Tools

Torque Wrenches - Ideally one big and one small (My 1/2" one is in the range of 30-150ft/lb,
Two reasonably large adjustable wrenches
Breaker bar circa 2ft in length
Socket set(s) that accommodate as small as 8mm sockets and as large as 21mm. Recommend additional six sider of the following: 19mm and 21mm
OPTIONAL: Ratchet Spanners
Masking Tape
High Temperature Silicon Sealant (I used the Mazda one)
Cable ties
Cable snips
Kitchen Foil/Cling Film
Elastic bands
Pliers/long nosed
Several Newspapers
Kitchen Roll
A wooden spoon
STRONG awl set (for replacing Oil seals) - The Draper awl set will suffice, but the handle will come off if you are heavy handed)
Torx bit set or screwdriver set
Screwdriver Set
Box Spirit Level
Fishing tension weighing scales
Oil/Coolant Drain Trays (Recommend both)

Some observations before you start

Store parts logically, with their securing bolts and brackets and if applicable in the order you removed them.
Label everything.
Torque everything correctly - If you are going to do it - do it properly!
Take lots of pictures and/or video as much as possible. This makes it much easier to retrace your steps.
Here we go:

Preparation/Removal of parts:

  • Chock rear wheels and jack front of car. Use axle stands.
  • Remove under tray. Jack front of the car. Approximately 9-11 bolts ( 8mm and 10mm) from under the car.
  • Drain oil: Loosen sump nut but don't remove. Similarly loosen the oil filter (under the inlet manifold). I was lucky - mine was hand tight - access isn't great. Remove filler cap, remove sump plug, drop oil and leave to drain. Once done, replace sump nut with new one if necessary or replace the washer on the old one. Replace oil filter and be prepared for it to try and spill oil down the side of the engine as per normal fare with oil filters. Be prepared to catch spilled oil and remove the by now, leaking filter from the bay asap. DON'T replace oil at this stage, but DO remember to do it at the end of the process!
  • Remove radiator cap and drain coolant from the bottom of the radiator (Philips Screwdriver cross on bottom of radiator), store coolant.
  • Remove air intake pipe (2 x 10mm Captive Pipe clips), Disconnect pipe connecting to cam cover (Pliers). Remove clip that serves as a tie for the pipe.
  • Put foil/cling film over MAF and throttle body openings and secure with elastic bands or cable ties.
  • OPTIONAL: Remove Radiator and Fans - Very easy to do and as you are draining coolant anyway, there isn't any real impact of doing so. Disconnect the coolant pipes at the thermostat area and at the bottom of radiator (Pliers for hose grip clips). Disconnect two electrical connectors for the fans and label with masking tape so you don't forget what they are for.Two bolts for the rad stays (Either 12mm or 14mm - can't remember). Radiator and fans lift straight out.
  • OPTIONAL: Drop ARB - I personally had to do this as I couldn't undo the crank bolt (My ratchet/breaker wouldn't clear it). 4 x 12mm bolts and it will swing down slightly and rest on components further down. You can see the room gained in the below pic - I haven't dropped the ARB yet and you can see how it restricts access to the crank bolt:
  • Remove the two water hoses connected to the thermostat housing.
  • Remove tower brace if applicable (4 x 12mm)
  • Remove HT leads and coilpacks from the top of cam cover. If you are likely to forget then label the cylinder numbers on the leads using masking tape, however, it's pretty intuitive. Tuck the loom leads for the coilpacks out of the way at the back and remove the clip attaching them to the cam cover.
  • Remove plugs using a 10mm plug wrench.
  • Remove EGR pipe from cam cover and the PCV Pipe.
  • Disconnect the large VVT oil feed banjo bolt (19mm)at the rear of the engine bay. There are two washers on this assembly. BE CAREFUL to catch the right-most copper washer otherwise it will fall when you remove the bolt.
  • Remove electrical connectors on the cam cover - One is near the "Oil Control Valve" for the VVT mechanism on the front left of the Cam Cover (Near the black plastic tube). Another is at the left rear of the cam cover
  • Remove the 11 10mm rocker bolts (careful with these - heard many reports of these snapping).
  • Put some newspaper down in anticipation of removing the cam cover. Grabbing the cam cover by the bracket at the right rear of the cover (which the HT cable clipped into) and the front "hump" that covers the cam sprockets, lift the Cam cover directly up and clear of the engine bay. Place it on the newspaper as mentioned. Cover the exposed valvetrain in foil.
  • Remove Air Conditioning/Power Steering belt (Mine has A/C but I know many do not, this guide caters for A/C models in any case): Firstly loosen the bracket nut on the tensioning mechanism (no need to remove). This is the nut on the bracket that the long bolt screws into. Next, loosen the pivot bolt on the power steering pump. This is done but loosening the nut shown in the picture below. If the belt is not removable now, you need to give the power steering pump a bit of "persuasion" to move. Lightly tapping a club hammer on a socket extension on the top right of the pump will do this. Remove belt and label it should you need it for reference later.
  • Remove the Alternator/Water pump belt: Loosen the three 10mm water pump pulley bolts now or you'll be re-tracing your steps later. Use a six sider if possible because these bolts burr easily. You want these finger tight. Similar to the A/C and Power Steering belt, you need to back off the tension on the belt using a very similar process on the alternator - I.e. the order being Bracket nut, Pivot Nut and Long Bolt. So,loosen the tensioner bracket bolt at the front of the Alternator, then loosen the pivot bolt on the back of the alternator. Access is a pig, and is from behind the alternator. You can see the bolt protruding through the front bottom-right of the alternator.Trace it back to the rear and try to undo it with a stubby spanner (14mm).If tight you may need to get under the car and hammer a spanner to free it. Bit of plus gas won't hurt either. After this, loosen off the long bolt to the end (but again no need to remove). The alternator should drop, but if it doesn't, you'll need to "persuade" it as per the Power Steering pump.Remove belt and label it should you need it for reference later. I didn't get a great pic of this area but you can easily work it out from the pic below:


  • Remove the water pump pulley by undoing the small bolts you left finger tight earlier.
  • OPTIONAL: If you are doing the camshaft oil seals or at the very least inspecting them, at this time I would crack the camshaft sprocket centre bolts too as these are a pain in the backside later and are easier when locked in place with the belt still on. I strongly recommended the use of an adjustable wrench on the camshaft whose bolt you are trying to loosen get a friend to hold this and brace it whilst you use a socket/spanner and a club hammer to shock these bolts free. With the inlet camshaft on the Mk2.5 VVT - you'll need to undo the three Torx screws which hold the centre cover and gasket on the VVT mechanism on the end/front of the inlet camshaft. Once removed, you'll see the camshaft bolt. BE CAREFUL here. If the wrench slips out of your friend's hand here, it will hit the cylinder head and dent the soft alloy. (2017 Update: Mx5parts now sell a camshaft locking tool - well worth the money: )
  • Crack the crankshaft pulley bolt (21mm use a six sider).This can be tough. I found that many brackets on the market that lock the crank in position won't fit for the Mk2.5 as the bolts are recessed. I put the car in 5th gear and used a breaker bar and a club hammer. I find that "shocking" bolts loose with a hammer by breaking corrosion works best for me. Not sure is this is great for the car, but it worked and I've noticed no ill effects.
  • Remove the crank bolts and then remove the Crank pulley. Refit the crank bolt and do it up finger tight to the woodruff key so that you can turn the engine over still using a ratchet.
  • Remove the upper cambelt cover by removing the 4 x 10mm bolts. Retain the brackets and store the bolts with the cover.
  • Remove the mid cambelt cover by removing the single 10mm bolt on the left.
  • Remove the lower cambelt cover by undoing the two bolts (10mm). Make a mental note that the right hand bolt also fastens a cable retaining bracket.

Finding Top Dead Centre

  • Finding TDC for Piston 1 on the power stroke (From now on - in this guide TDC = "TDC for Piston 1 on the power stroke": There are several ways to do this and I'll try to describe it as clearly as possible.

    First some trivia:

    The crank sprocket rotates TWICE for each SINGLE rotation of any given cam sprocket.

    During ONE rotation of the camshaft sprocket, piston 1 (and indeed all pistons) will reach Top Dead Centre TWICE. This is due to the fact that in the stages of the combustion cycle for a four stroke engine, the piston needs to compress the air/fuel mixture AND push the ignited exhaust gases out of the cylinder at separate times in one cycle. The reason you need to know this is because you want to find TDC on the compression stroke and not the exhaust stroke.

    Gently lower your wooden spoon handle first into the spark plug well of piston 1 (nearest the front bumper). The spoon will provide a visual indicator as to when the piston is rising and falling. When you turn the engine over in the next few steps, you'll notice the spoon rising and falling as the piston pushes it on it's journey.

    Essentially you should be at TDC Piston 1 on the Compression stroke when:
    The nearest cam lobes to you (cylinder 1) are pointing at 9 O'Clock and 3 O'Clock respectively AND
    The "E" on the Exhaust cam sprocket (right hand sprocket) is at 12 O'Clock AND
    The "chip" in the crank sprocket lines up to the arrow on the engine block at 12 O'Clock AND
    The "I" on the exhaust cam sprocket - it's corresponding tooth if you follow it back to the engine block, lines up with the "I" on the engine block face AND
    On the inlet cam sprocket, there is a marked tooth - this again, if you follow it back to the engine block should align with the "E" on the engine block face
    Your spoon is at the highest point.

    The picture below shows my engine at TDC:

    Close up of sprockets (after I'd marked them) - N.B. The "I" mark at 8 O'Clock on the exhaust sprocket and the line at 4 O'Clock on the inlet sprocket don't appear to line up to the marks on the block in the photo, but this is due to the camera viewing it at a slight angle - :


    Here I'm looking straight on the exhaust sprocket and you can see everything lines up:


    And at the crank sprocket here's a pic I took (again it appears slightly off due to the camera being at a slight angle):

  • Once you have achieved finding TDC - get your phone/camera out and take lots of pictures of how things look, taking particular attention to the Inlet cam sprocket as it has no letters on it.

Marking Sprockets and the Old Belt

  • Now you need to mark everything up. This is a point where things are different for the VVT engine of the Mk2.5. In other guides you will note that both cam sprockets have letters on them. This isn't the case on the VVT engine as the presence of the VVT mechanism on the Inlet side means a different cam sprocket is used to the older engines and there are no visible letters.
    The by far easiest way to get everything bang on, is to mark the old belt with Tip-Ex when the engine is at TDC Piston 1. Mark on the belt where 12 O'Clock is on both the cam sprockets.Choose either the nearest tooth of the belt or sprocket to the right of 12 O'Clock.Draw a line seamlessly on the cam sprockets straight onto the belt. This will allow you to ensure that the new belt lines up perfectly when you copy over the markings. Also mark the belt at 6 O'clock of the crank sprocket on the tooth corresponding to the "U", you shouldn't need to mark the sprocket itself as it is smaller and more difficult to get wrong but if you want to make it subtle (this reduces the risk of interfering with a tip I have for tensioning the belt later). So now you essentially have a belt with three marks which will tell you how many teeth apart everything is from each other. This is illustrated in the following pics:

    Take lots more pictures of everything with the marks drawn on, so you'll have reference later.
  • Now what you can't tell from looking at your existing belt as is, is the forces acting on it from various components. If you were to slacken the cambelt tensioner now and remove the belt, everything would not want to stay as it is. This is because the valve springs on the various cam lobes are pushing backwards and forwards (trying to rotate the camshafts in various directions). The only thing stopping them achieving this, is the cambelt. This is why, in other guides, you'll see guys trying to use adjustable wrenches - attached to the camshafts at specific hex points and either clamped or cable tied together to hold the camshafts in place.
    I had a lot of difficulty with this, I didn't have G clamps at the time and my various attempts to cable tie the wrenches together failed (wrenches slipped). By all means try that method at this point to hold everything together, hopefully you'll have better luck than me - in any case it should affect your success with the job - just make things slightly more difficult (2017 Update - Using this tool will make your life easier here: )
  • Similarly, there has been much talk of cutting the belt in half and sliding the new belt on, then cutting off the old belt. Great idea in principle, but as I was changing the camshaft oil seals and water pump as well I couldn't do this (needs the belt to come off for a period of time.).

Cambelt Removal

  • At this point, loosen the cambelt tensioner bolt and push the tensioner pulley against the spring to slacken the belt off sufficiently to be removed. Ensure you are totally happy with how you've marked everything up and the abundance of pictures and video you've taken. Slide the old belt off.

Camshaft end oil seals Inspection (Optional)

  • These are a "recommended" job which I did but you may opt to skip this. I recommend that you inspect them at the very least for leaking, ageing and wear. My Mk2.5 is 12 years old and my camshaft seals looked in good shape but I did them anyways. It's a judgement call as replacing them isn't a nice job. Look at them and think hard as it's do or die. Once you start trying to get them out, there is no going back as you WILL destroy them getting them out.
  • The way I did them is to remove the camshaft sprockets by removing the bolts you loosened earlier. Make sure you keep them in order and the correct way around. Now look at the original seals, and inspect them. Make your choice. Take pictures of the seal. Take particular note of how far they are recessed into their seat. You will be replicating this depth of insertion.

Camshaft Oil Seal Removal (Optional)

  • Unfortunately I didn't get any pictures of the seals in situ which makes explanation trickier.Personally I then loosened the camshaft end cap bolts and then removed them with a small amount of WD-40 and a set of awls. I should note that both the use of WD40 and loosening those bolts may be controversial, as the WD40 will slightly contaminate the oil even with conservative use, so be careful and keep kitchen roll close by. With the end caps, people have debated with each other undoing these bolts and not any of the others puts stress on other parts of the camshaft. However this is the way I did it (as have others), and I noticed no ill effects. I strongly advise you read up and make your own decisions.
  • The technique I used to get the seals out is to start with the exhaust camshaft oil seal and effectively destroy the middle of the seal all the way around the seal (I.e. between the inner edge and outer edge where it is softest). Carefully hack away using a knife and the awls. Take your time and if you get angry or frustrated, make a cup of tea and chill out for 10 minutes or so. You don't want to brute force this and score the metal seat the seal sits in. Alternatively the service manual recommends covering a screwdriver in a rag and using this to gouge out the seal. I didn't do it this way so can't advise on it's effectiveness - just be careful!
  • Ideally, get to the point where the middle of the seal is largely destroyed and you'll find you can pull the circular spring inside the seal out. Then with a bit of WD40 and the hook awl you can gently start pulling it out. Be patient - it WILL come out. Rinse and repeat for the inlet camshaft oil seal - Same applies except it is bigger. It is worth noticing that if you buy the Draper awl set I used (from mx5parts) that they are far from bulletproof and will bend and break from the handle if you are too heavy handed.
  • In the below pic the red line is the area where I recommend to cut into to the seal. If you cut all the way round, you effectively separate the seal into two (an inner and outer) and you can remove them easier:


Camshaft Oil Seal Replacement

  • Push in the new seals using a socket or similar to achieve uniform insertion depth. You're trying to get it to be the same depth as the original was. Once complete, refit the Camshaft sprockets. Torque to(36-45 ft/lb).

Crankshaft Oil Seal Inspection/Replacment (Optional but highly recommended)

(2017 Update - It's a tough call as to whether to replace this if it isn't leaking - you mightn't want to rock the boat as it can be a pig to get the seal out. However, after having done this twice, i've come to the opinion that I don't rate the construction/quality of the seals very highly. There is a circular spring behind the face of the seal and it is very easy for it to become dislodged - I managed to dislodge it in the new seal just by holding it in my hand - see pic below)


The mangled part at the top is from me removing it with a screwdriver. You can see the cause of my leak - the spring had slipped at the bottom. This wasn't cause by the removal as the rubber had fatigued and didn't return to the proper shape when the spring was reseated by hand.

  • You'll need to remove the lightly tightened crank bolt, and then the woodruff key. The woodruff key may be slightly chamfered - check orientation. My woodruff key wasn't too bad to get out, but it it's corroded in, this could be a deal breaker for you as to whether to bother. If it's corroded in there are many stories of people having to grind off the sprocket. With me, I simply got some pliers, doused in Plusgas, and wiggled it up and down whilst pulling it out. Came out with little drama. You should then be able to pull off the sprocket and inspect the seal.
    Again Inspect it and make the judgement call - mine was leaking and I didn't have a choice. If you do it, then it's the same procedure as above but with worse access - you won't be able to look at the seal head on. Again, note how deeply set the current seal is. (2017 Update - I had to do this again recently and after reading the workshop manual again, it only took me about 2 mins to pop the whole seal out using the following method: I made a two inch cut into the seal as per the red line in photo above but in the 1 or 2 o'clock position of the seal - I then wrapped a medium sized flat head screwdriver lightly in masking tape, pushed it in and pressed towards the floor and it popped straight out in one piece. Not sure if it was easier because the seal was "only" 4 years old, but it was much easier than last time using this method.)
  • Crankshaft Oil Seal Replacement - Push in the new seals using a socket or similar to achieve uniform insertion depth. You're trying to get it to be the same depth as the original was. If you loosened the end caps, then ensure you torque them correctly and gently. I have a friend who sheared one. Not pretty apparently. (2017 Update - I recommend the following method after discovering the problem above. Coat the seal, shaft and seal face lightly with engine oil. Initially install the seal by finger, and gently rotate it as you fit it over the shaft. This ensures a good seat and that you can see any problems with the spring. Pus it flush to the face of its seal and push in with a deep 21mm socket, gradually and carefully. You want the seal to sit inside the face by 0.5-1mm (so not much). I ensured uniformity by gently using an oiled wooden spoon.)
  • Replace the crank sprocket and fit the new woodruff key.

Replace Water Pump (Optional)

  • Follow the guide on for this:
    My only observations are:
    Check shaft for play/resistance, if in doubt replace it. I did.
    Use OEM Mazda pump - fair few reports of dodgy aftermarket quality and bad/non-existant fitment. Do you really want to have to take it all apart again because it leaks? Allegedly you only need a liquid gasket for the Mazda pump, but I got scared and ordered an aftermarket gasket and used liquid gasket sparingly to seal it. No leaks. Ensure you order the coolant inlet flange gasket and be careful scraping the old one. I'll also say that other guides mention replacing an O ring down the side. I didn't mainly because I forgot to order it.
    Once replaced, ensure the shaft spins freely. All bolts regarding the water pump (mounting and inlet flange) should be torqued to(14-19 ft/lbs)

Replace the Thermostat (Optional)

  • Easily done by opening the housing. Scrape the gasket carefully and install a new one.


Fit new Cambelt

First a collection of relevant diagrams for the following section:


  • Ok, so now you're ready to fit the new cambelt. Firstly whilst everything is off, replace the idler and tensioner pullies with the new items, ensure a good fit and torque the idler correctly(27-38 ft/lb) - fit the tensioner and do up the bolt finger tight. Refit the spring on the tensioning unit (ensure correct orientation) but bolt the tensioner so that it is LOOSEST on the belt, so push the tensioner pulley AGAINST the spring (to the left) as much as you can and tighten the bolt in the pulley so it stays there.
    Get the old and new cambelt and put them up alongside each other. Transfer your three Tip-Ex markings across to the new belt. Ensure that they are tooth to tooth accurate. Several times. Count the teeth.
  • Firstly, line up the solitary crank tip ex mark on the belt (which is furthest from the other two tip-ex marks) with the bottom of the crank sprocket on the tooth where the "U" is. If you remember this should be directly opposite the TDC "chip" on the crank sprocket directly below the "U". Once this is achieved, get some cardboard and wedge it between the belt and the shelf on the bottom of the block to lightly hold the belt in place whilst you route the belt around the cam sprockets.
    Keep the belt tight and route it around the idler and then onto the exhaust camshaft sprocket. Ensure that the timing mark on your belt lines up with the one on your camshaft sprocket.
  • This is where you might need some help if you couldn't lock the camshafts in place previously using the adjustable wrenches. (2017 Update - Buying the cam sprocket looking tool negates the below) Having fitted the belt on the exhaust cam successfully, you are now trying to line up the inlet mark on the new belt with the mark on the inlet cam. However, as mentioned before, the inlet cam will not want to sit in place without some persuasion. If your wrenches locked successfully, you are sitting pretty, if like me you couldn't do this, this is how I got the belt on correctly.
    You'll need help, so call someone. In preparation, attach an adjustable wrench onto the inlet camshaft on the hexagon section.
    Next I asked my wife to hold the belt on the exhaust cam sprocket with her finger whilst I routed the belt around the tensioner and nearly onto the exhaust cam sprocket.
    I then stood next to the offside wheel (facing the engine bay side on) and took over from her holding the belt on the exhaust sprocket with my right hand and with my left hand I was able to pull/push on the attached camshaft wrench. I then told her she was to line up the belt tip-ex mark with the inlet sprocket tip-ex mark, and slip the belt on when I applied force to the wrench in order to line it all up. It sounds complicated but it isn't - I kept the belt on and applied force to the inlet camshaft - she simply had to put to belt on correctly. Congrats, your belt is now on. Release the tensioning pulley spring slowly and let the spring take up the immediate slack in the belt. Hand tighten the tensioner bolt (This is temporary - you'll be tensioning the belt properly later)
  • Verify correct cambelt fitment and alignment of all sprockets: Using your ratchet on the crank bolt, turn the engine over twice at the crankshaft (not at the camshafts - remember that the crank spins twice for each camshaft rotation) - so that the crankshaft "chip" comes round twice and stop it at the arrow on the block. The tip-ex marks on the inlet and exhaust sprockets should be at 12 O'Clock on each. Please note that the marks on the belt will be elsewhere - this is normal as you've cycled the engine. You are merely checking that after you've rotated the crank twice, that the marks on the sprocket are still exactly as they were at TDC when you started. Similarly, as above, the following should be true:

    The "E" on the Exhaust cam sprocket (right hand sprocket) is at 12 O'Clock AND
    The "chip" in the crank sprocket lines up to the arrow on the engine block at 12 O'Clock AND
    The "I" on the exhaust cam sprocket - it's corresponding tooth if you follow it back to the engine block, lines up with the "I" on the engine block face AND
    On the inlet cam sprocket, there is a marked tooth - this again, if you follow it back to the engine block should align with the "E" on the engine block face

    You are looking for any discrepancy - if you were a tooth out when fitting the belt, it will be noticeable, but only if you look hard. Make sure the above conditions apply. Note - if you want to double check or if you accidentally over rotated the engine, you can turn over the engine as many times as you like - just make sure that you stop it at TDC.

Tensioning the Cambelt

  • I and others have had lots of fun with this (namely the belt being too tight) and have had to re-tension, and so it's really important you do this right first time if possible. (2017 Update - I've found that this is because the aftermarket tensioning spring I used is too strong AND the fact that the tensioning pulley doesn't move smoothly across it's path - it can get stuck even with the bolt backed off. Be prepared to have to re-tension the belt - particularly if you don't have the means to measure the belt tension)
    At this point you should be 142% sure that the belt is on correctly, that everything aligns wonderfully, and that you are at TDC again.
    Now, you need to turn the CRANKSHAFT sprocket (not camshafts) one complete turn AND then 5/6ths of a turn. It may just be me, but I read this and scratched my head several times. Again, this relates to the two cycles the crankshaft does for each turn of the camshafts. You need to be at this precise point (I.e. which is essentially just before 2 complete turns of the crank sprocket) in order to tension the belt properly. There is an tensioning indicator mark (See earlier diagrams) on the block which shows you where the "chip" in the crank sprocket should align to, when you are at the correct point (I.e. this tensioning point should be roughly at 10 O'Clock as you look at the crank sprocket, just behind the belt). The purpose of spinning the engine to exactly this point is because at this exact point in the engine cycle the various forces from the valve springs and crank ensure that the belt is completely tight at every point EXCEPT the side where the tensioner pulley is. Hence precise tension can be applied as there is no slack elsewhere.
    MAKE SURE THE "CHIP" ALIGNS PRECISELY TO THAT INDICATOR - This is how it should look when you are ready to set the tension:


    So to re-iterate, from TDC you spin the CRANK "chip" past the tension indicator once, and then stop it exactly on the tension indicator the next time around - that's your 1 and 5/6ths of a turn.

    OPTIONAL: At this point I recommend a tip I wish someone told me. The "chip" should be pointing to exactly the tension indicator mark. Right, now get your tip-ex and mark on the crank sprocket where the TDC indicator arrow is now (approximately 4 grooves to the right of the "chip"). The purpose of this is if you have to strip the engine back down to re-tension the cambelt at any time, you won't have to take off the crank bolt, crank pulley, and lower cambelt cover off in order to accurately set the sprocket to the "tension set" mark. This is because you can now accurately see that the engine is on the tension mark whilst looking down into the lower cambelt cover by ensuring the tip-ex mark is aligned with the TDC arrow on the block. (The lower cambelt cover when assembled, obscures your view of the tension indicator) so now if you have to re-tension, you can just make sure that the tip-ex mark you made corresponds to TDC and you'll know the crank sprocket is precisely on the tension set mark. See below:


  • Right, back to where we were - applying the tension. Release the tensioner pulley bolt to allow the spring to apply the "correct" tension to the belt. Ensure that the pulley does not stick or judder as it tensions the belt.

    Tighten the tension pulley bolt to lock the amount of tension in. Now the reason I put "correct" in inverted commas is that whereas in an ideal world, this should be it and it's job done, it's not an ideal world.

    I and others have found that a new spring can tension the belt too tight. Time to check the tension.

Measuring the tension

  • You need to rotate the CRANK 2 AND 1/6ths from where it is (it's currently at the tension set mark). So essentially you are returning it to TDC and then turning the crank 2 more times around and returning the engine to TDC. Not entirely sure why this is but I'm assuming that spinning the engine in this way distributes the slack evenly around the belt, ready for you to measure the tension.
  • The tension is measured between the two cam sprockets by gauging how much the belt deflects from horizontal when a predetermined force is applied to the belt in the middle of the sprockets. But how to measure it? My first thought was "if I'm taking all these bits off, I want to make damn sure that I do it right first time". So I looked around for a cambelt tension gauge. And promptly found them to be suitably money rinsing, especially this side of the atlantic. Furthermore, the problem with the MX5 is that it seems to be rather unique in the amount of force it asks you to use in order to try and deflect the belt - 98N or 10kg/f with an acceptable deflection range of 8.5-11.5mm. A quick look at the operating manual of the "Laser Cambelt Tension Gauge" shows both the force and the deflection outside the capabilities of the product. Dayco Krikit gauges are popular across the pond, but seem to only cater for ribbed or v belts. They might be fine but i wasn't going to take the punt unless I was sure.
  • (2017 Update - I found the best way to check this without a suitable gauge is to buy a fishing scale like pictured below. It is possible to wedge it in upside down just to the right of the coolant pipe/ thermostat) and gently use the hook to exert the correct amount of force with one hand. By laying a box spirit level across the top and holding a metal ruler to measure the gap with my other hand - I was able to gauge the deflection as 10mm which was perfect - no more cambelt whine. You can then verify by the "calibrated finger method" should you wish)


    So whats left? The "calibrated finger" method - 10kg is a lot of force for a finger to exert. However, what I also discovered is that the belt will not deflect significantly more if you exert more than this force. I roughly figured that if i had my hand out in front of me (I.e. I did not use my body weight to apply more force onto my finger), then around 10kg is roughly how much force I can exact. This situation is far from ideal, but all I really had to go on.
    So to apply this to the belt: I put a spirit level across the back of the camshaft sprockets, leaving at least half the belt still exposed. When you do this it will flatten the belt which may have some slack in it which may in turn cause it to bow slightly. After all you are measuring deflection from horizontal. Then use a tape measure or ruler and rest it vertically on the thermostat pipe. You can now use it to measure the belt's resting measurement on the ruler and then subsequently it's deflection when force is applied.
    Apply your 10kg thumb/finger force, and you'll find that after 8kg or so the belt will not substantially deflect more (barely if at all). You can re-calibrate on the fly if you keep your scale in a reachable place whilst measuring. Obviously if you are unable to deflect the belt at least 8.5mm, then the belt is too tight. If you can deflect it more than 11.5mm, then it's more likely too loose. If it's within the range, rotate the crank twice to get the engine back at TDC and check again. Check as many times as necessary to be happy.
    If you need to re-tension, then assuming you are at TDC, you'll need to spin the engine 1 and 5/6ths just as before to the tension indicator mark. Either reset the tension by loosening and re-applying the spring tension, or should you do this several times and find that the spring is either too tight or too loose in applying tension, you may need to use your finger to "help". Be VERY careful whilst doing this though, it may even be worth trying the old spring to see what result that gives. Again, lock off the tensioner and rotate the engine 2 and 1/6th at the crank to check the tension. Rinse and repeat until you are totally happy. Torque the tensioner pulley bolt when done (27-38 ft/lb).


    Putting it all back together. Largely as the Haynes manuals say "Refitting is the reverse of removal".
    Refit the lower cambelt cover remembering that the right hand bolt also secures a cable retaining bracket - finger tighten the bolts for this cover. Then refit the crank pulley. Refit the main crank bolt. I applied threadlock to the thread, put the car in gear and torqued it to specification 116-122 lb/ft.
    Refit the middle cambelt cover and ensure it doesn't rub on the belt or pulleys. Again, hand tighten these bolts for the moment.
    Refit the top cambelt cover ensuring that the right two bolts are securing their cable retaining brackets as per before. Hand tighten again.
    Tighten/torque the cam covers in the order below. These, if tired and worn, can potentially rub on the belt. Refit carefully and don't over tighten.


    Refit the water pump pulley. Torque bolts to 69-95 INCH lbs.
    Regarding the cam cover gasket. Clean the cover and change this if you bought a new one. It shouldn't be difficult to prise out. Apply high temp sealant in the areas shown below where the gasket effectively raises around the cam end caps and the cam position sensor at the back. This prevents oil leakage at these points.


    Install the cam cover back. Try to ensure that you lower the cover squarely and evenly. Push down and gently move the cover to ensure you are properly on and have a good fit. Finger tighten the cam cover bolts and tighten in the order shown below . Again, these bolts are fragile and you should tighten these gently and only a little each time. I typically tightened these one-by-one and found that when I had got back to the first one, it was loose again due to the force exerted by the others. Tighten iteratively to specified torque (44-78 INCH/LBS)


    Refit plugs and torque (11-16 ft/lb)
    Refit coilpacks, leads. and electrical connectors
    Regarding accessory belts, these can be tensioned in the same manner as the cambelt in terms of measuring deflection. you can also gauge their tightness by twisting them at their measurement point. If you can rotate the belt past 90 degrees from rest, then it's likely to be too loose. Ensure once tensioned that you lock off both the bracket bolts for the tensioning mechanism and the pivot bolts for both the alternator and power steering pump.
    Refit the radiator/fans (Bolts =14-19 ft/lbs)
    Reinstall the coolant hoses securely and their clamps. Refit the fan electrical connectors.
    Reinstall the air intake piping and hoses going to the cam cover.
    Refit the ARB.
    Fill the radiator with coolant and ensure that the overflow tank is topped up.
    Refill the oil.
    Other guides will tell you to check the timing and ignition speed at this point, possibly using a timing gun. You don't have to do this on the VVT engine as this is sorted by the ECU using sensors.
    Double check EVERYTHING and when ready try and start her up and celebrate/cry. Check for leaks (both coolant and oil wise). Check for airlocks in the coolant system and gently squeeze the top pipe to try and force them out.
    Whining: If you hear whining like in the following video at any point in the rev range, chances are your cambelt is too tight:
    It's unlikely to be the cause, but it's a good idea to remove air intake and then the drive belts at this point and start the engine, to eliminate them as the cause of the noise. Don't run the engine for too long as your alternator obviously won't be charging the battery.

Re-tensioning the cambelt

  • Assuming you made the tip-ex mark I suggested above, you'll just need to remove the following to adjust: Intake, plugs, electrical connectors, coilpacks/leads, cam cover, top and middle cambelt cover and possibly the alternator belt. This will give you access to the tensioning pulley. You shouldn't need to remove anything else assuming you followed my tip-ex tensioning mark tip earlier.
    To re-tension, you shouldn't need to remove the ARB unless your socket/ratchet doesn't give you enough clearance.
    If you followed my tip-ex tip, you can rotate the engine to TDC as before - then rotate the engine once at the crank and then line up the tip-ex mark on the crank sprocket to the TDC arrow on the block by looking down into the lower cambelt cover with a torch. You should now be at 1 and 5/6th rotation

    (2017 Update - A tip here is before you release the tensioning bolt to re-tension, draw around it (particularly on the left side if your belt is too tight and is whining) with tippex (preferably using a brush) that way, when you release it and re-tension, you have a point of reference from before. Assuming you follow the procedure as I did and it's still too tight (whining), you can back it off millimetre by millimetre until the whining goes and/or the deflection is within spec.).

    Re-tension accordingly as before, spin the engine 2 and 1/6th as before, measure tension as before and re-assemble. Hopefully this time you'll be bang on.

    Good luck!

8 Posts
Discussion Starter · #3 ·
Hehe, remember the above guide covers the water pump, the crank and cam oil seals, and drive belts - all optional.

If you changed nothing but the cambelt, you can do it in 40 mins if you don't hang around!

2,350 Posts

26 Posts
I must write little correction of your guide to avoid anybody (like me) from undo 4 screws on VVT mechanism - there are only 3 torx screws on VVT mechanism camshaft cover with gasket (like you could see on photos) which you need to remove for acces to undo camshaft bolt when you want to exchange VVT camshaft seal.

Anyway great write up, I just done this on my vvt engine following your guide.

1 Posts
Hi Supertoucher,

Thanks for this fab write up! Really appreciated! A couple questions if I may?

  1. The Haynes Manual says you have to remove the Oil Control Valve Casing from the Camshafts Cover, but I don't see why and from your description, you didn't seem to have to do this? Grateful for confirmation.
  2. Why is it necessary to find TDC on cylinder 1? Is it not enough to make sure that the sprocket markings line up with their respective positioning marks?



1,533 Posts
Not got this engine but I still read it! Well done :thumb-up:

A lot of work gone into writing this up worth "pinning" mods?

8 Posts
Discussion Starter · #9 ·
Thanks lads for the kind words - haven't been on here for a while but have email notifications set up.

It's very wordy I know and could probably do with editing to make it a bit more reader-friendly. I'll see if I can put some time into it this week and make the changes that the guys above have noticed.

It's really not too bad a job looking back on it - don't be afraid to give it a go - but make sure you have the correct tools - I would have used a cam sprocket locking tool if it was available at the time -

Thanks again for looking!

8 Posts
Just to advise that i've re-visited this today as i've had a leaking front crank seal for the last month or so - causing a bad oil leak (and a mess). Thus, i've taken the opportunity to update, refresh and correct the guide.

Some very late replies:

Elektron - edited as per your request - thanks for pointing that out!
1905Adam - 1.) If you mean the unit on top of the front left of the rocker cover as you are looking at the engine in situ - I can confirm there is no need to remove this before removing the rocker cover.
2.) Trying to have a think as to whether it is necessary or not but my brain is struggling today - it might not be necessary but given it was 4 years ago that I wrote this guide, any chance of me remembering is gone i'm afraid.

Just to re-iterate - the guide is really, really wordy and it's a bad habit of mine so don't be put off doing this job. I finished doing a timing belt job on my Evo a couple of months ago and it makes this seem like childsplay. I really believe that the MX5 is probably the easiest timing belt job you can do compared to most cars of it's era with the minimum of risk.

The guide could easily be made more concise i'm sure. However, it does cover pretty much EVERY optional job you can do whilst doing the timing belt, so you could easily cut the guide down by half if you were JUST doing the belt.
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