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Whirring Noise After Cambelt Change - Setting The Tension


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#1 baker556

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Posted 03 May 2020 - 06:06 PM

Hi all

 

I've changed the cambelt, water pump and pulleys on my mk1 1.6 mx5 long nose.

 

Following this guide, I've set the tension for the cambelt:

 

This from the "Garage Section":
# Turn the crankshaft 1 5/6 turns clockwise
And align the timing belt pulley with the tension set mark.
# Tension the belt
Loosen the tensioner bolt to apply tension to the belt. Tighten the tensioner bolt to 37-52 Newton Meters.
# Turn the crankshaft 2 1/6 turns clockwise
Verify the timing marks are still correctly aligned.
# Check belt deflection
Apply about 22 pounds of pressure to the center of the belt between the camshaft pulleys. The deflection should be 9-11.5mm. If not, repeat from the tension setting.

 

Also looked into this guide that was helpful:

https://www.mazdabg....ts__Tension.htm

 

Anyway the belt is still making a whirring noise, sounds like a supercharger, the belt is obviously tensioned too tight or could it be the sounds of a new belt that needs wearing in?

 

Thanks


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#2 Jim A

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Posted 03 May 2020 - 08:09 PM

So you just loosened the tensioner bolt, let just the tensioner spring do the tensioning all by itself without any outside assistance, and then retightened the tensioner bolt?  If so, that’s the right way to do it as far as I understand.

 

Is it possible the noise you are hearing is a bad bearing from an idler, alternator, p/s pump, or a/c compressor?


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#3 baker556

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Posted 04 May 2020 - 08:11 AM

Exactly that, loosened the tensioner bolt, let the spring take the tension then torque back up.

 

New pulleys, belt, water pump - have adjusted and slackened both the alternator and p/s, a/c pumps.

 

It gets louder with the revs so must be over tightened belt somewhere, would a video assist?


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#4 dadbif

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Posted 04 May 2020 - 11:12 AM

Sounds right, I installed mine at TDC, turned the engine over a couple of times, stopped at belt tensioning mark, then let the spring set tension.
Try again, don t think you’re doing anything wrong, new spring? Try it with the old one...
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#5 Jim A

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Posted 04 May 2020 - 03:19 PM

What brand of timing belt did you install; the blue Gates Racing Timing Belt is known to be noisy.

 

Did you replace any of the other belts?

 

Assuming you didn’t use the Gates Racing belt, and didn’t replace the alternator or a/c p/s belts, you can eliminate the alternator, p/s pump, and a/c compressor bearings as the source of the noise by removing their belts and BRIEFLY running the engine without them.  I say briefly because without the alternator belt the water pump doesn’t turn, and running a motor without circulating coolant can damage it, but for the 30 seconds needed to test for noise there will be no harm at all.  If removing the belts eliminates the noise, spin each component by hand and feel for a not-smooth bearing.

 

Alternatively, use a mechanics stethoscope (or use a dowel or whatever you have on hand) and listen at each rotating component for a bad bearing.  It’s not as positive as removing the belts, but it’s a lot easier.  If there’s any doubt you can always remove the belts.

 

If the accessories bearings aren’t the source of the noise, and you didn’t install an inherently noisy cam belt, well, you’re back into the timing chest.  I like dadbif’s idea to use the old spring for tensioning.


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#6 1outof5

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Posted 04 May 2020 - 08:57 PM

My dad used to put a few drops of oil on a belt at a time to « hear » which belt was making noise


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#7 baker556

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Posted 05 May 2020 - 11:12 AM

Jim A - like the idea of removing the other belts then starting, might try this..

 

The kit is from Mx5 parts to be exact:

 

1 x Aftermarket Timing Belt
1 x Aftermarket Tensioner
1 x Aftermarket Idler
1 x Genuine Mazda Tensioner Spring

 

https://www.ebay.co....353.m2749.l2649

 

1 Genuine mzda tensioner spring, unfortunately I threw the old parts in the bin.

 

Just a thought, would it matter which way round the cambelt fits? 

 

I'll try the stethoscope idea, but almost certain the noise is from the cams, meaning over tensioned belt, unsure of the idea of the oil :/

 

Thanks


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#8 dadbif

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Posted 06 May 2020 - 06:37 AM

You don’t need a stethoscope, use the dipstick, oily end against the bearing, handle against your ear...
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#9 baker556

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Posted 06 May 2020 - 09:52 AM

dadbif, will that work? Can only try, will get to it this bank holiday weekend let everyone know the result.

 

Has any one had a bad experience with a cambelt kit from mx5 parts?


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#10 dadbif

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Posted 06 May 2020 - 11:29 AM

Yes of course it does, was standard practice at RR to detect engine noise
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#11 Jim A

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Posted 06 May 2020 - 01:10 PM

A dipstick stethoscope is an excellent idea, but won’t engine oil get puked out of the dipstick tube when the engine is running?  Maybe a rag over the end of the tube is reasonable precaution against that.

 

Pretty much anything will work as a stethoscope; a dowel, a wooden mixing spoon, a metal rod, a wooden leg.  Just don’t get it, or your hair, or your beard, tangled up in a moving belt.


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#12 dadbif

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Posted 06 May 2020 - 03:59 PM

Oil out of the dipstick tube? FFS, only if his piston rings are shot and pressuring the crankcase.
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#13 Jim A

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Posted 06 May 2020 - 04:32 PM

Oil out of the dipstick tube? FFS, only if his piston rings are shot and pressuring the crankcase.

So a 50/50 shot then if I try it with my cars.  Probably don’t want to try it with a R75/5.


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#14 dadbif

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Posted 06 May 2020 - 09:00 PM

Why not, it’s common practice, works just as well on a bike engine as a car...
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#15 Jim A

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Posted 06 May 2020 - 10:50 PM

With a boxer motor both pistons move in together, so with each revolution of the crank your displacing the volume of the engine displacement through the oil fill hole.  Do that 10 or 12 times a second, and something’s going to leave the crankcase.  You might not particularly notice on, say, a BSA Golden Flash (with apologies to BSA enthusiasts, of which am one), but many a BMW rider would probably be apoplectic with an oil mist outside of the crankcase.

 

I guess that my unfamiliarity with using a dipstick as a noise conductor results from always having something more suitable at hand in the garage.  The beauty of the idea is out on the road, in an emergency, when you need answers but most tools aren’t handy.


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#16 dadbif

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Posted 07 May 2020 - 07:58 AM

The beauty of a dipstick as a diagnostic tool is that it can be inserted into small spaces far beyond the reach of a hand holding the end of a stethoscope, and you always have it with you when driving.
My favourite bike engine of yesteryear was the Vincent, last worked on one in 1965 when I fitted a Black Shadow engine into a Norton “featherbed” frame
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#17 Jim A

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Posted 07 May 2020 - 03:03 PM

Ah, the Vincent!  When I was younger, and became aware of the Vincent, I went looking for one.  When I found one for $10k, I had only $5k. When I had finally accumulated $10k, they were $20k; when I saved $20k they were $40k, when I had $40k they were $80k and so on, and so on.   Now that I can finally afford one no matter what the price, my body so worn out I can’t ride one.  I should have been born rich instead of good looking.

 

 I did own a bevel gear driven overhead cam Ducati 900 Super Sport, which is probably as close as the world has ever come again to the Vincent.  Open intakes, kickstart only, long and low, and glorious overhead drive gear whirring, intake sucking, and exhaust blowing, sounds.  After that a succession of Ducati singles, Guzzi V7 police bike, 70 Triumph Daytona, many airhead BMWs, a HD Sportster (which gave me planters fasciitis), a Hinckley Bonneville (which was surprisingly well engineered and built and nearly indestructible), and a number of Asian imports.  But there was nothing like that ‘78 Ducati SS.


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#18 atlex

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Posted 07 May 2020 - 08:28 PM

Also a spray bottle with water in it is great for checking noisy belts. Just give a blast of water and see which one quiets up ;)


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