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Re: timing chain and valve cover oil seal Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Mon, 7 Jan 2002 08:51:23
In Reply to: timing chain and valve cover oil seal, nt moore, Mon, 7 Jan 2002 00:27:11 Members do not see ads below this line. - Help Keep This Site Online - Signup |
With the valve cover off is the best time to inspect the chain. First, rotate the engine by hand and inspect the chain for wear - same with the cam sprockets. Wear looks, like, well, wear. Next, turn the engine to TDC for cylinder #1, and check the mark on the cam sprockets against the alignment mark on the head. If they line up well, the chain isn't worn or 'stretched'. If the alignment is off, the chain is worn.
The Bentley 900 16V manual has a nice section on this inspection. Also look at http://216.78.172.244/engine_folder/incarchainpg1.htm, from the Townsend Imports site - it's a service bulletin on changing the timing chain in the car, but it also talks about the inspection, or at least where the marks are. I don't go by the Saab notice about determining wear by how extended the timing chain tensioner is - I go by the alignment marks and visual signs of wear.
Saabs tend to be rattly engines, so there are a lot of things that could be causing the sound. Yes, a worn timing chain is one of them, but there are plenty of others. As 9K Wrencher says, it could be the chain tensioner. Try this trick - by hand, turn the engine BACKWARDS a couple of turns. This may clear the rattle right up. The tensioner extends in discrete steps, and you may be just at the edge of a step. Turning it backwards can cause the tensioner to re-tension the chain.
Is the occasional rattle when cold, and/or only at idle? It's common for the engine to rattle some when cold - not only timing chain, but the hydraulic lifters take time to pump up, and lifter noise sounds pretty similar. If it rattles at idle, check your oil pressure (put an oil pressure gauge into the system) - low oil pressure can cause the engine to be rattly.
Replacing the chain tensioner isn't too hard, and a new one is only about $50. There was an upgrade to the chain tensioner design around '88, and if you have the old style, it's worth converting to the new one.
You can change the chain with the engine in the car, without removing the chain cover. The service bulletin in the link above tells how. But if the chain is worn, so are the chain guides. You could replace the chain, but if you keep the guides, the engine will still rattle. You can replace the upper chain guide easily - it's mounted on the underside of the valve cover. I replace them when I have the cover off. The other guides can only be replace by removing the chain cover, which is a lot of work.
Inspect the chain with the cover off, and if the alignment is off, replace it. I'm a beliver in a full change - chain cover off - because a worn chain usually means worn guides. But so far, I've never had to replace a chain. I have an '88 that a dealer mechanic said 'needed a new chain, right away' because it sounded loud. No inspection, just by ear. That was, oh, the mid 1990's. The chain inspected fine with the valve cover off, and I've put another 70K or so on it since - original chain.
Good luck!
posted by 140.157....
, Mon, 7 Jan 2002 17:05:12, Mon, 7 Jan 2002 08:51:23 <-- Viewing This Message
, Mon, 7 Jan 2002 12:08:31
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