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My first mx5 an NB

3237 Views 32 Replies 6 Participants Last post by  guitaristanime
Hi all,

I started my mx5 journey fairly arse about face when I decided I wanted to rebuild an engine, having never done so before. I've done engine swaps and some repair work but never fully built my own. So I had a look round and found a suitable VVT to use.

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I wanted to essentially just rebuild make slightly better, clean everything up and lap the valves etc. Spec was pretty much stock besides some forged rods in case I decide to go FI in the future. Overall the engine seemed to be in good condition, fingers crossed. I did the work and added a baffled sump plate as well to help with track work. Once that was pretty much done I started to hunt for a suitable car to drop the engine into.

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I picked up this 99 NB recently which seemed to be relatively rust free in the right places and having had some recent welding and paintwork. It's by no means perfect but I wanted the car to build a track focused machine from so seemed to fit the bill.

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The engine seemed to have a big misfire (more on that later) and after compression testing seemed very low on compression on the middle two cylinders Vs the others. No real matter the engine was a Bp4w Which was useful as I was thinking about using this head to play about with a skim, porting etc for another rebuild.

I used the car for a few short trips, the PAS was leaking badly, the misfire didn't seem to get any better and the brakes were also binding on the front left.

First job really was to pull the old engine, I removed the head first up to have a look if there was any visible reason for compression loss but couldn't see anything.

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It was only when I got round to the coil pack that I could see coil 3 was in 2's slot and vice versa. Likely cause of misfire found!

Anyhow I already had a fresh engine and so the bp4w was on its way out.

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An afternoons work later and the vvt engine was in place and ready to go. Everything buttoned up and she started second go after having realised the coil pack was plugged in the wrong way.

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Everything looked good until I saw a cascade of oil coming out the front of the block. Disaster.

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Much work later and having cleared the alternator out of the way I could see the oil pump had cracked and was leaking catastrophically. An expensive and time consuming mistake to say the least.

Another day later and I had the engine pulled and back on the stand. In undoing everything I had somehow left the old mushed up o ring in place as well as the new o ring leaving them no room, tightening down obviously resulted in the crack. Lesson learned.

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I've ordered a boundary billet gear pump to replace it which should be here on Tuesday so fingers crossed I can have it back together and in the car for then.
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numbers are not everything, if you can drive it then thats what matters:cool:

remember,it's torque that gets you around corners and uphill ;)

Finally got the new head on the car. Got fed up of waiting for the new shims for the shim under bucket conversion, so used the standard set for now, will just mean I can't yet go over the stock rev limit which shouldn't be too much of an issue yet.

Took a bit of time to get everything switched over, and adjusted well but think I’m there. Ended up using an endoscope camera to check I had plenty of valve clearance, especially when the intake cam is on full advance, as the valve is cracking open whilst the piston is still on the way up the cylinder but looked fine. Potential to skim the head further in the future to increase compression as well, but not sure by how much yet.

Was very nervous on first start up given what was at stake. Made sure everything was spinning freely then turned over without spark to make sure I had oil pressure. Then gave it a push and it started up straight away, not even any lumpy idle which I was kind of hoping for lol.

Had a bit of trouble getting the vvt to start working again, then remembered the stiffer valve springs likely meant the vvt needed more duty, so that started working again following a few tweaks to the mapping.

Anyway, now been out and mapped a few times and it's pulling a lot harder. Redline is still at 7400 for now, so more to come, but feels quite a bit quicker at top end, suddenly comes on strong after vvt at 5k revs or so and sounds a lot more intense than it did. Virtual Dyno suggests 160bhp but not quite sure whether that's right just yet.

Still keeping the exhaust bung in for now so potentially losing some horsepower there too.

Next job is a better exhaust manifold, and do some port matching work to the Jenvey inlet manifold as I think there is a bit of a step to the head which won't be helping things.
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Good improvement from last time, hopefully bit more to come once subs arrive.

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Lots of work on this car of late, but not much actual progress. Recently fitters a new GCfab roll bar unfortunately didn’t receive the lower spreader plates so it’s in place but not fully secured as yet.

The engine is also out for a rebuild, whilst looking at the cams I found a tiny flake of metal, so pulled the filter apart abs found some more so decided to pull it out. Had a set of 85mm 12:1 pistons waiting anyway so it was a good excuse to rebuild. Ended up finding a very worn set of thrust bearings so that was the root cause. Anyway block has been to the machine shop and is ready for the rebuild and inevitable piston crown grinding due To valve contact.

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In the meantime I decided to drop the subframe while the engine was out and address the rust. Front chassis rails had been patched but were clearly very bad underneath it all don’t have any pics but will get some and front repair sections are in the post.

While everything was out made sense to refresh bushes and de rust all the arms. Lots of work on the wire wheel later I’m getting there on those. Silver car and silver wishbones. Not sure whether that was wise but wanted something other than black.

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Looking better now, excuse the oily mess.
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One chassis rail done now. I’d always thought they were ok, but had just had patches welded over and some thick sealer, so we’re a mess underneath. welding not the finest but seems to be doing the job.

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Decided to repaint pretty crudely engine bay. Wires tucked behind wings and new galvanised subframe installed now.
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Front suspension coming back together now. Ended up buying new upper arms as they both needed new ball joints, and cost of those seemed half way to a new full arm. Removed rear subframe this afternoon as well and removed all the rust from that and the arms. Will be painting that tomorrow, then polybush and reinstall in the next few days.
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Front is back on the ground now, just need to reinstall steering rack then that’s broadly done.

Rear subframe and arms back on, just waiting on new diff and crown/pinion before putting the hubs back on and buttoning everything up. Once done can then focus on getting the engine finished.

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All back together and working so far! 4.7 diff makes a big difference, gears feel very short. Virtual Dyno now saying 200whp, not sure how accurate but feels a fair bit quicker. Need to get some proper dyno time to fine tune.

That rips, love them subframes too.

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How many hard tops would you like? $1600 rare as rocking horse shit m9
$1900, plus $300 delivery m9
I love how about a year ago this was a massive exaggeration for comic effect, and now that same seller is legit asking in excess of these prices ...
I love how about a year ago this was a massive exaggeration for comic effect, and now that same seller is legit asking in excess of these prices ...
oh sweet lord, you aren't wrong

what else did we predict??
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