Noise from timing belt area diagnosis EDIT SOLVED

Technical Area Engine, Transmission, Exhaust etc
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  1. My model of MX-5 is: Mk1 1.8 1995
  2. I’m based near: Cambridgeshire
  3. I’m looking for technical help or recommendations on: Noise from timing belt area

Hi all,

I have a Mk1 MX-5, and did the timing belt / water pump / tensioners / pulleys etc on my driveway this summer. It was my first time doing this job, however took the task seriously and followed a number of tutorials / books etc, and I’m relatively confident that the timing and tension was correct once finished. There were 19 teeth between the cam gear top markers, the inward facing markers lined up well with those on the case, and the tensioner was tightened in the position with the crank rotated once fully then lined up with the ~10:30 oclock tensioner marker on the case.

After putting the car back together, it seemed to run and sound fine, but it has started making a noise when the engine is cold which is not good, and I think may be growing worse. Once the engine has warmed up properly, it sounds pretty normal

T0min - Immediately after starting when the engine is completely cold there is a pretty loud growling noise from the belt area. This lasts a minute or so and doesn’t sounds great at all.

T4min, T8min - After 4 mins of idling, there is no growling at all, and is replaced by a fast intermittent ‘clattering’ noise which comes and goes in waves. This lasts for around 10 minutes while the engine slowly warms up.

T40min (after driving home) - Once the clattering noise has died down, I drove back from work (~30 mins) and there was no concerning noise in the cabin or unusual behaviour or feedback from the car at all. On parking, the engine sounds I would say normal, maybe a little of the intermittent ‘clattering’ noise but not enough that I would notice it without looking out for it, it is quieter than the lifters in this state.

I’ve attached onedrive and Google Drive folders both containing videos taken at T0, T4, T8 and T40. The growling sound is a fair bit more prominent in the video than in person, and the T40 running sound does sound less healthy in the video than in person, that said the growling and clattering do come out relatively representatively.

Does anyone recognise the symptoms described / noises shared and have a suggestion as to what it could be? I’m thinking a timing belt tensioner or idler pulley may be bad and creating this noise, but it’s vague enough where it could be the belt itself, the gates water pump or even piston slap (maybe?) The aux belts and associated pulleys and bearings seem to be tight enough, stable and correctly fixed.

Unfortunately I am booked into something where I should be in theory driving from Cambridge to Manchester on Friday, but I think I may need to hold off until I know things are okay.

If this rings any bells for anyone and they have any recommendations for what I may be best checking first, I will be immensely grateful for any advice anyone can give.

Many thanks for reading,

James A

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Just to say, I don’t know how OneDrive is when sharing compared to Google Drive, but with Google Drive you can set it so that anyone with the link can view/download etc. from a specific folder or you can set it so that only people who you accept can access your files, through signing in with their Google Account first.

Your OneDrive folder is currently locked behind a Microsoft login page, perhaps there’s a setting to make it 100% public without requiring a Microsoft account first?

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Good catch thank you, I’ve edited the post and added an unrestricted google drive folder link too

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Someone with more experience can probably answer, but one thing that I noticed - and I don’t know if it’s an optical illusion - is that at one point in T4 when the camera is relatively still, it looks like the crankshaft pulley is ever-so-slightly moving in and out (into the engine/out towards the radiator).

Also the noise does seem to get louder the closer you get to the pulley, and possibly during a run as things heat up, maybe the metal is expanding and tightening thus reducing the noise.

I’m no expert (I too have only done this job once on my own '95/'96 car, my disasters can be found in other threads I’ve posted) but I’m wondering if maybe the bolt isn’t torqued right, or maybe something like the woodruff key needs replacing.

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Take the alternator / water pump belt off and run it briefly to see if you still get the noise.

If you don’t, it’s either the water pump or the alternator (I suspect alternator).

While the belt is off, see if you can feel any roughness rotating the water pump or alternator by hand. It’s not necessarily a clean bill of health if you can’t, but a smoking gun if you can.

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I’ve experienced a brand new timing belt tensioner pulley “growling” when fitted, albeit not on my MX-5.

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I had a similar issue recently with a brief clattering sound at start up . Car on 52,000 mls.

Turned out to be the main pulley bearing. Had a new main pulley, tensioner and serpentine belt fitted and all is quiet again. Mechanic showed me the old main pulley bearing wear by giving it a spin by hand when I went to collect the car. Jolly nice having a reliable mechanic!

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Thank you for this methodical approach recommendation, it definitely made sense to isolate the easily isolatable parts to make the diagnosis more localised.

You were bang on the money too, it was the alternator bearing which was damaged! I was able to get an immediate click and collect new alternator from Bofi and install it today, and it’s now running well!

I think my mind first jumped to worst case scenarios rather than sensible / likely ones, glad it turned out to be a comparatively easy fix!

1 Like
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Thank you to everyone who commented and took the time to help me, it was greatly appreciated! As most suspected, it was a bearing, and thankfully the one on the alternator so not too significant a job to fix.

Benefit of being in Cambridgeshire, I was able to click and collect a new alternator from Bofi in under an hour which meant that I was able to fix it today, they were also able to provide some guidance for the install which was handy!

I noticed the bolt attaching the alternator bracket to the water pump was not well connected, meaning that any forces normally taken by this fixing was instead absorbed by the pulley; this was likely the root cause for the part failing, that and age. Something to watch out in future! Also, worth mentioning that the alternator lower pivot bolt might not be removable without first removing the air inlet manifold bracket which sits behind it, but this isn’t too bad; only three bolts

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Glad you managed to sort it so quickly :+1: