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G10 timing belt question; Belt not running in center of pulleys
Topic Started: Aug 16 2012, 11:16 AM (694 Views)
Sparky
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If there is already a thread on this question I couldn't find it.

I changed my belt yesterday with a new Goodyear belt and new idler. Upon removing the cover I noticed that the old belt (61,000 miles) looked as good as new but it was overhanging the pulleys by about 3/16 inch. I figured the idler pulley bearing might be worn a bit. It wasn't.

The new belt also runs in about the same place in spite of adjusting the idler tension from the full relaxed position to where it should be. Going into this I will state that the new belt was as tight as it needed to be even when the idler was in the fully retracted position. It is the same belt that I took off (same part number) so I guess it's just manufacturing tolerance.

Pulley wear? Are the crank and cam pulleys supposed to be slightly crowned or flat? The wisdom of my fellow Metro buzzers is needed here.

Thanks
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starscream5000
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Got 70 MPG?

The pulley will naturally try to walk off the gears when the engine is running. The crank pulley prevents this from happening. The belt should naturally butt up against the backside of the crank pulley after running for a few moments, so the belt should be almost flush with the edge of the camshaft gear.
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Sparky
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starscream5000
Aug 16 2012, 11:19 AM
The pulley will naturally try to walk off the gears when the engine is running. The crank pulley prevents this from happening. The belt should naturally butt up against the backside of the crank pulley after running for a few moments, so the belt should be almost flush with the edge of the camshaft gear.
Ok. Thanks. I watched it idle without the cover on it for maybe one minute since I didn't have any other belts back on it yet. Are you saying that the belt will float back to the center after a few minutes or at higher speeds? Maybe I'll remove the cover, reinstall the water pump belt, and run it for a few minutes to see what happens.
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starscream5000
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Got 70 MPG?

No, it will move to the very edge as the crank pulley is what's keeping it from walking off.
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Sparky
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starscream5000
Aug 16 2012, 02:37 PM
No, it will move to the very edge as the crank pulley is what's keeping it from walking off.
OK. In the morning I'll check it out again. From what I've witnessed it is running with about 3/16th inch of the edge of the belt off the pulley to the outside. (away from the engine) It doesn't offer to go any further than that though. Running like this I cannot feel any vibrations indicating that it's touching the cover.

Thanks.
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Memphis metro


Forgetting to tighten the bolt thru the pulley will also cause belt sliding.
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Sparky
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blue rhino
Aug 17 2012, 01:19 PM
Forgetting to tighten the bolt thru the pulley will also cause belt sliding.
Yeah, I thought of that. Thanks.

Being the usual impatient person that I am, I decided to brave the heat and go out and check it over again instead of waiting until the cool of the morning. I removed the top four cover screws so that I could flex it outward enough to see the belt as the engine ran. Low and behold, it's running in the normal position now.

The only conclusion that I can come up with is that a new belt might have a tendency to run to one side or the other until it's been tight on the pulleys for a time and takes a "set" so to speak. Presently it's running with the outside edge of the belt on the edge of the cam pulley. In any case I appreciate the suggestions that you guys have offered. I appreciate it.

Now all I have to do is prepare to pull the engine out of my El Camino and freshen it up. I'm having to take the Total Seal rings off the pistons and skip them across a convenient pond. They cause some oil usage. (dirty rotten mother frigging pieces of metal) :rasp

Thanks
Sparky
Edited by Sparky, Aug 17 2012, 01:46 PM.
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