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Worn Cam Shaft Timing wheels ?  Rating:  Rating
 Posted: 05-28-2014 07:42 pm
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21st Post

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 325
Barthol wrote:
As you can see the belt now moved towards the engine and is flush with the rear of the pulleys.

Is this normal, or is there a way to control that the belt stays in the center?
There is no adjustment that will move where the timing belt tracks. It is what it is. Ideally, the belt should run in the center of the pulley, but it rarely ends up being ideal.

I understand you purchased pulleys from Lotusbits, but are they J-H, Lotus, or aftermarket replacement pulleys? Even though they might "fit" (as in, bolt on), not all pulleys have the outer rim centered on the hub in exactly the same way; so it may be that the pulley rim moved, not the belt.

For example, in around 1979 (?) Lotus re-drew their own pulleys in order to "metricate", and took the opportunity to slightly change the hub to rim relationship. With all else remaining the same, and in perfect condition, simply switching from older to newer production Lotus pulleys will slightly change were the belt 'appears' to track on the pulley... but it will be the pulley that moved.

Having said all that, it's not normal for any Lotus 9XX belt to run on the edge as shown in your photo. I suspect something else is at play there.

If everything about the engine is straight, parallel and per the design drawings, then the belt will track in plane with the small drive sprocket down on the crankshaft. The belt won't move with the cam pulleys if the pulley offset changes. So that begs the question, when you replaced the pulleys, did the belt move, or did the pulley rims move?

On the other hand, if the main bearing bore, block deck, head or cam carriers are machined out of alignment such that the crank and cams aren't parallel when assembled, then the belt will track off the cone of the non-parallel center lines.

The most frequent cause is having the head skimmed to flatten the bottom surface. When the head warps, the whole thing warps like a banana, not just the bottom. If only the head's bottom is skimmed independent of everything else, then the bottom may be flat, but is it still parallel to the camshaft... wherever the camshaft moved to during the warping. If not, then the cam will no longer be parallel to the crank, and the belt will track toward the convergence of the crank & cam center lines.

Similar but different, if the stud that mounts the timing belt tensioner pulley is bent or it's mounting hole is drilled out of parallel with the crank & cams, then the belt will walk off the resulting taper.

All working axis must be parallel. If not, the belt will walk out of alignment with the drive sprocket on the crank.

If your belt isn't wandering back and forth as the engine runs, then there's no cause for concern if it runs off center. At least as long as it's not hanging over the edge of the pulley, and stays were it is without wandering.

Last edited on 05-28-2014 07:51 pm by Esprit2

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 Posted: 10-22-2014 10:44 am
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Joined: 07-11-2013
Location: Hannover, Germany
Posts: 26
I just realised that I still have the federal cam timing (115-115) and I was going to change it back to european spec (110-110)
Do I have to adjust the ignition and carburettor set up after changing timing?

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 Posted: 10-22-2014 03:43 pm
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Jensen Healey
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Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 983
The ignition timing should be checked if the belt is removed from the auxiliary sprocket.

The carburetors should be fine but it never hurts to balance them.

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