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Old 02-18-2009, 04:14 PM
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Question M103 engine belt tensioner: testing one?

I have a belt tensioner from my parts car. Tensioner was working when it was removed about 2 years ago. Is there any way to test a tensioner when it's not installed, i.e., sitting on my workbench?
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Old 02-18-2009, 04:49 PM
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I just went through this on an M104, same tensioner assembly as the M103. The pully is obvious, if the bearing is smooth/tight/quiet, and the dust cover is still on the front of it, you're probably fine.

The spring on the other hand, has been a pain for me. Mine wasn't tensioning the belt, beyond the limit of the adjuster nut. I removed it and compared the orientation of the flats to the photos on several (Worldparts supplied photo) parts suppliers' sites, same photo, showed the flats generally in an orientation where the plane would pass between the two ears on the tensioner. Mine is roughly 90degrees to that (click on buy parts above to see what I mean). In a pinch, a weekend, I removed one from a parts M103, found it to be in about the same orientation, but better by several degrees, and it tensioned the belt properly. Both tensioners had good spring force when the flats were clamped in a vice and tensioner rotated.

In summary; I don't think that you can tell without installing it or comparing it to a known good one.
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Old 02-18-2009, 06:01 PM
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Yeah, I tried comparing the "flat" location to a picture on one of the parts supplier's web site. It gave a pretty good idea where the flats should point. One thing I found out the hard way is that the arm that attaches the asjuster rod to the back of the tensioner can be slipped on the tensioner flats backwards, resulting in very little adjustment range.

Also, I had a tensioner fail with no warning at all - except that it was 16 years old. Instantly stranded, with no makeshift way to go anywhere.

DG
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Old 02-18-2009, 06:11 PM
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Quote:
Originally Posted by Ron in SC View Post
I have a belt tensioner from my parts car. Tensioner was working when it was removed about 2 years ago. Is there any way to test a tensioner when it's not installed, i.e., sitting on my workbench?
I believe it is "tested" via the correct torque setting -- so no.
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Old 02-18-2009, 06:28 PM
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Tensioner in photo is the spare I may use, I think it's newer and has less miles on it than one in car now.
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M103 engine belt tensioner: testing one?-picture-039.jpg  
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Old 02-18-2009, 07:37 PM
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Originally Posted by Ron in SC View Post
Tensioner in photo is the spare I may use, I think it's newer and has less miles on it than one in car now.
Compared to my old one that has the broken/torn rubber, it sure looks good. Of course the true test is when it is installed and tightened to the correct tension.

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Old 02-18-2009, 07:39 PM
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I wish my spare looked like that! Looks like it is oriented properly, I'd hang a large wrench on the flats to be sure it moves smoothly with immediate strong spring torsion, call it a very good spare.

Or, call it an un-known used part and sell it to me for cheap.
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