Worry about whirry noise? (timing belt tension and pulleys) - Miata Turbo Forum - Boost cars, acquire cats.

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Old 04-23-2010, 12:37 PM   #1
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Default Worry about whirry noise? (timing belt tension and pulleys)

Does anyone actually try to meet the factory spec of 8-11mm (from memory) slack in the timing belt when installing a new one? (see attached diagram below)

It seems that if I follow the spec (turn crank to this point, loosen then tighten tensioner), the resulting slack is a lot less than the 8 mm minimum. I always only get like 5-6 mm if I follow the tensioning instructions. So when I assembled my engine I got smart and "cheated" on the tensioning instructions to get 8 mm.

While troubleshooting a light load misfire, I noticed that the cam phase the AEM was reporting on the VVT was jumping around. In order to eliminate a loose timing belt I went in and re-tensioned it as per the manual, (easy without a water neck), and got 5 mm again.

I'm not sure it's my imagination, but I now get a whirring sound most audible at around 1500~2000 RPM... which when I took a hose to my ear, sounds like it's coming from the tensioner. Sheesh .... I looked around my engine parts, and it looks like I mistakenly re-installed a 75k mile tensioner instead of my 30k mile tensioner ....
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Old 04-23-2010, 07:17 PM   #2
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I just tensioned it according to the manual and the deflection seemed "in the ballpark" with a new gates racing belt. I just made sure there were 19 teeth between the pulley marks with everything aligned and let the spring do its thing.

I could see an old tensioner or idler whirring a bit if used with a tight new belt. If it were me I'd probably dig in there again and install the new part, but I'm obsessive like that. And like you said, it's a little less of a pain with the water neck removed.

It's been about a year since I've done it so my memory is hazy but I'm pretty sure the tensioner bolt goes through the water pump body. I guess what I'm saying is make sure it's not the water pump whirring from an overly tightened WP/alt belt. Had that happen once on my truck.
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Old 04-23-2010, 09:13 PM   #3
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I used my "Cricket" to set alternator belt at 50 lbs ...
However it is an easy check to loosen it a bit...
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Old 04-28-2010, 03:56 AM   #4
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Turns out it was my timing idler pulley.
When I tightened the belt beyond spec it started making noise.
I replaced it, and did a quick start and listen with the timing belt covers off. Quiet.
Now my timing belt slack is between 8 and 11 mm.
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