Re: Timing Chain wear allowance

Posted by DavidPackard On 2020/6/21 21:41:11

Tim;

I believe the crankshaft sprocket and the camshaft sprocket marks will align at #1 TDC (many engines do), but from a technical perspective the system does not demand that relationship. The goal is to correctly phase the crank and cam shafts, and the sprocket marks are used for that task. If the engine happens to be #1 TDC then OK that's good information, but the sprocket marks take precedence.

The shop manual section that details the procedure to check camshaft timing could/should be followed. That would be a second independent check to confirm you have correctly installed the timing chain. When I install a timing chain, or timing belt I will frequently misalign by one tooth and try to figure-out if I could tell the difference, and then put it back where it belongs once I know the difference one tooth makes. I will also roll the engine two revolutions several times to verify the alignment marks 'come back together. Remember one tooth 'off' is a sizable offset that should be obvious. Unlike modern interference engines you can't do any real damage if the cam timing is incorrect during some timing mark experimentation.

I also believe the shop manual procedure is there as a diagnostic check to absolve of indict a loose timing chain without the expense of pulling the timing cover. Other than the cold versus warm requirement the timing check could be conducted as routine maintenance during lash adjustment.

I guess I would need to know if the valve lash was set before or after the oil pump and distributor were installed during the initial assembly of the engine. I could easily be talked into the engine was parked at the static timing position (something like 6 deg BTDC) until the distributor was installed so the ignition timing could be set. Then spin the engine a couple of turns while the valve lash was set.

In closing Ross is absolutely correct, only the sprocket marks matter when setting the phasing between the crank and cam shafts.

dp