Lotus Elan

Timing Chain Adjustment Tips Please

PostPost by: Craven » Thu Apr 15, 2021 1:29 pm

Fascinating how when the workshop manual illustrates where and by how much the chain total movement is assess, other chose to disagree.
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PostPost by: billwill » Fri Apr 16, 2021 1:36 am

The diagrams are drawn by artists, not mechanics.
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PostPost by: rgh0 » Fri Apr 16, 2021 3:08 am

Craven wrote:Fascinating how when the workshop manual illustrates where and by how much the chain total movement is assess, other chose to disagree.


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 :lol:

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

cheers
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PostPost by: Craven » Fri Apr 16, 2021 11:13 am

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.
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