Note: This article is contributed by EB, our local machinist-in-residence.
I keep seeing the same problem with the same causes over and over. About 1% of new timing chain installs fail, pick any brand.
So here are some "Don'ts" instead of a "Howtos."
The problem we see is the chain running loose and noisy, if left without correction the chain eventually breaks or the guiderail, yes, even a steel one, will snap.
Chains very rarely just "break", there is always a cause.
Typically one of the
following is the reason:
1. The top left oil upper pump holddown bolt protrudes through the cover, this jams the tensioner arm. (Wrong bolt, too long, common error)
2. The tensioner holdown bolts are over-torqued(12# is suggested) the shaft housing is measured in clearences of fractions of a thousandth of an inch. Distortion is the result of over tightening, this jams the arm as the engine warms.
3. Dirt, debris, silicone, sealers, tiny metal or plastic filings, same result. Cleanliness is a requirement here, be sure to clean the oil pan, too.
4. Resurfaced head/block results in added extension of the tensioner. Of course the oil fed tensioner is simply a hydraulic reservoir, too much surfacing defeats the oil
hydraulics and failure results. If the tensioner arm is overextended at rest, you must use a thicker head gasket or replace the head if the thicker gasket is not enough to correct. About .040" is the maximum possible to remove when combined with a thicker head gasket, even at this maximum your camshaft will retard by around 2°, not a happy situation but runable.
5. Lower than normal oil pressure/obstruction of an oil galley.
To identify a loose running assembly, note excess wear on nearly every other
tooth, and heavy wear on the tensioner arm facing. If present, you have a misassembly/install error. Of course a defect is possible, we have had tensioners handed to us "leaking" out of the back access hole plug. Of course, not enough oil could leak there to be of a concern, I check new ones and the ALL leak a tiny amount there.
Defects are rare but obvious, the shaft does not slide freely when operated by hand. If it does not or even feels funny, don't put it in.
If converting the stock type nylon driver's side gaurd to the heavier steel type, it is best to use a fastner like a couple of old oil pan bolts. While the nylon design does float slightly, the steel guide needs to be secure. (Yes, I know, our kits don't as yet have those fastners, I am working on that.) Suppliers can be stubborn.
Note that the steel guard does come in two designs, one has the holes for the late engine only, one design is drilled for both early 83-84 and the late. I personally don't like using the dual drilled piece on the 83-84 engine, I say it is too short but what do i know?
The problem with the dual drilled piece is it can be tipped slightly, this places the bottom of the steel gaurd closer to the chain as ir rotates around the crank gear. if running loose for some reason, it can catch which spoils your weekend.
Everyone who owns one of these vehicles will sooner or later deal with a timing set replacement.
Hopefully this piece will help reduce the 1% or so that diagnose a "defective" tensioner after a disaster.....*EB
*Beats the he** outa me!....*LOL**...
Edited by kewlynx (01/12/06 08:41 PM)