I have tried the search facility but have not succeeded in finding help - apologies if i missed the obvious.
I have a 1971 Sprint.
The last couple of drives I’ve noticed on start up a ‘whine’ (not quite a ‘thrash’) from the timing chain. I’d like to check it’s adjustment.
The workshop manual basically says adjust the tensioner in or out for the least noise…which seems to me a rather broad description, given the wrong adjustment could be problematic to say the least.
Should it be done with a cold or hot engine and I’d really appreciate any tips to get it right please.
See viewtopic.php?t=26441&f=39&start=0#p175063 about half way through that long message as you are not actually doing a clay test, just refitting the cam sprockets and timing chain.
I suggest that you lift off the cam cover, so that you can feel the tension in the top section of the timing chain, instead of trying to guess it by the sound.
Sorry, Bill, I missed your first post with the link.
“Then the tensioner adjuster was screwed in to tighten the chain until I had just half-inch up & down movement in the chain at the top between the sprocket wheels”
First time I’ve adjusted one myself so I’d appreciate a double check since (compared to my only chain adjusting experience on motorcycle drive chains!) it seems quite tight.
The manual quotes a movement of half an inch which taking into account the thickness of the chain means very approximately 1/16th of an inch upwards and downwards from the edges of the chain. This meant tightening mine.
I turned the engine over to ensure it was consistent and rechecked a couple of times for peace of mind.
Frustratingly, I still have the noise, and will start a new thread since I can describe it a little more specifically now.
Sorry but you don’t need to take into account the thickness of the Chain.
It’s how much it moves midway between the two Cam Sprockets.
So moves up 1/4" and down 1/4" = 1/2" movement.
Hope that helps you.
good luck
Alan
I have always adjusted it to be a total movement of approximately 1/2 an inch up and down of either edge of the chain, i normally set it as the actual chain width which is less than 1/2 inch. It needs a little force to test this as the jackshaft needs to move and the inlet cam needs to move to ensure the slack is moved between the cam sprockets rather than lower down
Do a preliminary adjustment by the 1/2inch measurement method as per the workshop maunual and then use your ear for final adjustment with the engine running.
If it is too loose it will rattle because the chain is hitting the cam cover, on the other hand if the chain too tight it will whine.
The photos are really clear, thanks, Dave - and exactly what I did (with the addition of rotating the engine and re-checking, a couple of times, for peace of mind).
Interesting photo’s of method, If you look at the way the workshop manual shows, illustration given, you have a chain slack of ¾” not the recommended ½”.
yes I agree that it could be confusing to someone coming to it first time.
But it is only a drawing and the words in the top left do say . Total movement to be 1/2 inch. It is a case of being obvious once you know.
It is similar in a way to where in section J (brakes) page six it shows the brake master cylinder as nearest the R/H wing, when we know that is the clutch.
Remember we learn all the time.
Eric in Burnley
1967 S3SE DHC
I have observed the difference in the drawing versus the written text and also tested with various amounts of free play between the cams ensuring the other legs of the chain run are tight.
My observation was that around 3/8 inch total movement of the chain or around the width of the chain itself was good and produced low noise and never any tooth jumping issues. Going much tighter than this and certainly going to the drawing 1/8 inch of total chain movement caused the chain to whine. Going above 1/2 inch total movement caused the chain to start to rattle. I did not explore how loose you can run a chain before it comes off on a live twincam for obvious reasons
General chain tightening recommendations talk about 1/4 inch minimum or 2% of sprocket centres if larger of chain droop on a horizontal slack run between the pulleys away from the straight line between the sprockets. This equates to 4% or 1/2 inch of total movement above and below the straight line and this is consistent with my observations and the Lotus text recommendations.
All told I would trust the text not the drawing interpretation of the text
Personally I have taken the pragmatic approach of adjustment by sound where backing off from when chain whine starts, satisfactory.
As for standards methods for chain adjustment, measurements are usually given between the driven and driving sprockets, here on a Twincam the exhaust cam sprocket is an idler and the drive train is between the inlet cam sprocket and the crankshaft sprocket.
BTW The Workshop Manual apparently loves giving misleading guidance.
This is fascinating and just what I was looking for.
I adjusted my chain by translating the workshop manual as 1/2" total movement BUT including the chain thickness as per the diagram. Seemed very tight to me and sounded tight when running.
1/2" movement of any point seems much more logical - and the way I’d adjust my bike chains.
I’ll give that a go - thanks for the brilliant photo’s and the information.
