Chain howl

[MikeB]

Just done a top end rebuild on my SC engine, fitted new chains, started her up and have a chain howl which increases in level with revs.

Checked the sprocket alignment, all OK, cam sprockets seem to have little or no wear.

I didn't pre lube the chains, Andersons book seems to imply you actually clean them and put them in dry, but I left the lube that they came packaged in on them.

The engine has about 5 mins running since it was rebuilt.


Any thoughts, I have a set of cam sprockets ordered, but not sure that's the fix

[Nick Moss]

You have no choice but to remove the covers and see what's touching. Did you put the same number of shims behind the sprockets as came out? Did you use the workshop manual method to check the sprocket alignment? Show us a picture of the sprockets.

[MikeB]

Nick

Have had the covers off, didn't notice anything touching, same number of shims in as before, but different chain casing, so will recheck the clearances between casing and chain. Used the straight edge across the back, measured the distance into the casing of the intermediate shaft and then compared the two sprockets, all within 0.2 mm

[MikeB]

One thing I didn't mention, it has the oil fed tensioner upgrade, any chance that it is over pressuring? Anyone heard of the pressure release valve in the tensioner failing?

[911hillclimber]

I have had the one valve pop out into the engine!

The din was extreeeeeeem and certainly not a howl, but loud enough to panic and race to switch the engine off feeling. Thought I'd scrapped the re-build.

Took the silencer off, covers off and found the loose parts stuck in the chain cases by the oil. Lucky or what. Put the parts back together and made sure the ball was in the right place securely. this was 20 years ago so can't recall all the details.

The chains will have been drowned with engine oil as it gets an oil dose all the time, thus lubricated.

I would look hard at the alignment of the guides esp if you have changed them.
Easy to get one a 'groove' out or one that is not snapped over the head of its retaining bolt. On another engine this happened to me but I spotted it before running the engine.

The hydraulic tensioners were NEW!