cam chain tension

[JNS]

Is there a way of checking the cam chain tension without removing the rocker cover, and how tight should it be?
Thanks.

[jbcollier]

Not properly.  Best to follow the procedure in the manual.  Check your valve clearances at the same time.

[Grumblebuns]

I suppose a professional Lotus mechanic can set it by ear after he's done it a thousand times but for us mere mortals take the cam cover off and verify by measuring total slack per the manual, 1/2" total movement between the sprockets. The reluctance to remove the cam cover is understandable.
I've attached a drawing from the Elan manual of the timing chain.

[Lotuswins]

I've always wondered about that adjustment, and have two bent bronze idler gear fixtures to prove it....

So, to adjust it do you loosen the adjustment screw and pull up on the chain to get slack then tighten down the screw until the slack is the shown measurement?  OR:

Do you tighten it down until you can just pull the chain up and down, with the resistance coming from the idler gear spring tension, to the shown measurement.....

It would be nice if they included a procedure....

From what I've gathered over the years, adjusting while running is simply unscrewing the adjustment screw until you hear the chain bouncing off the valve cover, then tighten until it goes away, which seems awfully vague.

Jerry Rude
4005R

[jbcollier]

Undo the adjuster lock nut.

Move the adjuster in or out until the chain has the correct amount of movement.

Tighten lock nut.

Specified movement is the distance between the chain's upper side when it is pulled up, and the chain's lower side when it is pushed down.

It is possible for experienced TC mechanics to set the tension while it is running.  It is not advisable though as it is easy to get it wrong.  It is not done by loosening the adjustor until the chain is slapping then engine cases!  The chain does not need to be adjusted that often.  Just at the same interval as the valves need to be checked.

[Lotuswins]

Hi John,

So, you are saying the movement of the chain up and down are under spring tension, not a slack value??  And at the limits are actually pulling the tension to its limit? or bottoming out the piston that the tension spring pushes against???

jerry

[jbcollier]

Myself, I tighten the adjuster until the chain is taunt: I can't move it with hand.  I then back it off until the specified "slack" is achieved.  Then I tighten the lock nut, and that's it.  Nothing complicated about it at all.

[Lotuswins]

Maybe I'm overthinking this, but if you tighten the adjuster screw tight enough so you cannot move the chain up and down, you must have the spring coil bound, or the piston bottomed out?  so when you loosen it to the 1/2 inch chain travel, the chain is under tension, and centers itself/springs back?  If this is the method, then have you ever bent the bronze tensioner arm bracket after running for a period?? 

It seems I used to do it that way, but twice when doing something up there in the head, I found that bracket bent.  I have since went with an alloy bracket sold by Bean in hopes it would be less malleable, and was more cautious with the adjustment, such that it would move the distance required under slight tension only.  So far, so good. 

Jerry

[jbcollier]

I just use two fingers.  No issues.