Re: do timing chains strech or is it usually worn guides? - Saab 9-5 Bulletin Board - Saabnet.com
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Re: do timing chains strech or is it usually worn guides?
Posted by Stephen Goldberger [Email] (more from Stephen Goldberger) on Tue, 11 Feb 2014 07:49:40
In Reply to: Re: do timing chains strech or is it usually worn guides?, Gene N [Profile/Gallery]
, Tue, 11 Feb 2014 07:09:54
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not to be picky, but:
"Stretch" implies that the links are somehow longer than they used to be, like pulling on a rubber band. What happens is there is a sleeve between the pin an the roller, which wears, either through poor maintenance (abrasive or inadequate lubrication) or inadequate chains (early 9000 and C900 balance shaft engines). Yes, the chain gets longer, but it's wear, not "stretching," that causes it. The process proceeds slowly until the pitch (spacing between rollers) becomes too long for the sprocket to accommodate - then the roller engages with an impact that results in a massive increase in the wear rate and damages the sprocket.
We had this with the 9000, as I said, and many people looked at the broken pieces and concluded that the sprockets were too soft, causing the problem. Actually it was the other way around, and the problem was solved by changing the chain supplier. Note that the "bad" chains were from Saab's traditional supplier, the same ones that seem to last forever in the C900 and earlier 9000 2.0 engines. There seems to be a very fine line between lasting forever and lasting 50,000 miles, and whatever changes occurred between the balance shaft engine and the one that preceded it was enough to cross that line.
posted by 70.126.89...
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