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Re: Timing Chain Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 19 Aug 2004 13:33:22
In Reply to: Timing Chain, Alex, Thu, 19 Aug 2004 13:07:46 Members do not see ads below this line. - Help Keep This Site Online - Signup |
There is no time interval for replacing of the timing chain, like you would see on a timing belt. The timing chain is replaced 'on condition', which means if it's worn.
It's quite reasonable to have a timing chain last the life of the car, well over 200K miles. A critical element to long chain life is regular (frequent) oil changes. Low oil level and dirty oil kills timing chains.
Some folks change a timing chain based on it getting rattly. I know lots of shops that like to do that. The upside is that you get a new chain and guides. The down side is that it ain't cheap, and it may not have been necessary. There are a lot of things that can rattle on a Saab engine that aren't the timing chain. For example, the valves have hydraulic lifters, and a lazy lifter can rattle like a timing chain. And the most frequent noisy lifter is right next to the chain.
The chain also has guides. The top guide, mounted on the underside of the valve cover, dries out over time. This can cause a rattly chain noise.
The two methods for checking the health of the chain are to remove the chain tensioner and check the extension of the tensioner foot. This is an indication of a mixture of chain wear and chain guide wear. The method I like is to remove the valve cover and with the engine at TDC for cylinder #1, check the alignment of the marks on the cam against the marks on the head. Good alignment means a good chain. At the same time, you can visually inspect the chain.
Yes, this sounds like a lot of work. I like the direct inspection method. Usually the valve cover gasket is leaking anyway, and it's cheap. Remove and replace in an hour (including a look-around), and $20 for the gasket.
Doing a full replacement of a timing chain and associated components is about $800-$1000. Maybe a little less. You can replace just the chain by 'rolling in' a new one, but I don't recommend it, even though it's cheaper. The chain runs on many plastic guides, and runs on sproket teeth. I don't know of how a chain can wear, but not the guides and sprockets. So replacing just one part doesn't fix the problem, and worn guides or sprockets can still be a problem.
Yes, a broken timing chain is pretty bad for the engine. But at $1K a pop, I wouldn't replace the chain just because. If your engine is in the mid to upper 100K range, and the timing chain is making noise, I'd pull the valve cover and look. If it's making a lot of noise, try and rule out other factors (bad idler pulley, noisy fuel rail, etc), and if it still sounds like the chain, pull the valve cover and look.
posted by 192.249....
, Thu, 19 Aug 2004 13:33:22 <-- Viewing This Message, Fri, 20 Aug 2004 06:07:01
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