Timing Chain Adjustment Tips Please

[Craven]

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

[billwill]

The diagrams are drawn by artists, not mechanics.

[rgh0]

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

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
Rohan

[Craven]

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.

[XKR]

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.

[ivan.wood]

I know this thread is a little old but but thought I might get an answer.

Just checking the timing chain on my 1965 Elan and when the camshaft marks line up perfectly the crankshaft is about 5 deg past TDC. I don't have time to get a new chain and replace but would it be better to set it 5 deg BTDC?

[XKR]

I don't have my manual immediately to hand but if, as I think it probably does, require the engine to be set to TDC and the camshaft marks to be in line/facing each other, doesn't that just suggest that you're one link/tooth behind where you need to be?

Why wouldn't you just set to TDC, pull the cam drive sprockets off, index the chain round by one link and reassemble?

Check it all clears as usual and all still lines up and you'd be good to go.

[Niklas777]

Hi guys,

Reactivating this topic as the information shared here is very interesting.

To measure the 1/2 inch, what reference point(s) do you use on the timing chain?

In other words, do you calculate the tension from a single point (e.g. the top of the chain) or from the top of the chain for the top calculation and the bottom of the chain for the bottom calculation?

The result, of course, is different depending on the method and I find the manual confusing on this.

I'd like to thank you in advance,

Niklas

[rgh0]

See my comments earlier in this old thread. The drawing is inconsistent with the text and I go by the text.

cheers
Rohan