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Re: i had a lot of what i thought was timing rattle/tap Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 21 Dec 2004 07:25:00
In Reply to: i had a lot of what i thought was timing rattle/tap, aaron, Tue, 21 Dec 2004 06:59:53 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Timing chain noise is due to the timing chain thrashing around. It might get a little better when warm, because some things have expanded. Then again, it might not. Things are better lubricated when warm.
The Saab engine is pretty rattly. The upper chain guide (on the underside of the valve cover) dries out and shrinks, and that can cause a timing chain to make noise, even though there is no problem with the chain.
Probably the biggest reason for engine rattle is the valves, having nothing to do with chain health. The valves use oil as the hydraulic medium to eliminate clearance (and the need for valve adjustment). When the engine is cold, it takes time for the oil to pump up the hydraulic lifters with the cold, thick oil. When the engine is warm, and if the oil pressure is a little low (due to low engine speed, warm oil, and old, less viscous oil), the valves can rattle a bit.
I hate trying to diagnose timing chain problems by noise. I've had engines that a 'certified' Saab tech had told me was about to drop a chain, based on sound alone. I ignored him and kept driving. About 20K miles later, I did the valve cover gasket, and inspected the chain - it looked great. I sold the car about 85K miles later, still making the exact same noise, and running just great. If I can get 85K out of a chain on it's 'last legs', that's pretty good.
Timing chains are great, because it gives us something to worry about. At least a timing belt has a replacement interval - the chain usually lasts forever; occasionally they die early, and the results are pretty bad. Then again, timing belts fail, too.
There is a lot that makes noise in the engine, and frankly, unless the engine sounds like a tin can full of spoons rolling down stairs, I wouldn't suspect the timing chain. Could it fail? Sure - any vehicle that doesn't say TONKA on the side can break. But timing chains tend to be pretty good. Change the oil regularly (and frequently), keep the oil level up (Max or just a little higher), and the timing chain really is the last thing to worry about.
posted by 192.249....
, Tue, 21 Dec 2004 05:39:27, Tue, 21 Dec 2004 07:25:00 <-- Viewing This Message
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