What keeps a cambelt on

[paul_c123]

This is a weird one, and new to me. I fitted a cambelt to my latest victim, a Range Rover Evoque diesel. Part of the procedure is to turn the engine over 10 times, once the cambelt is in place and the tensioner is initially set. I am guessing this is to "even out" the position of the belt on the various gears and rollers, then a true correct value tension can be achieved. Yet when I did this, it was quite clear the belt was either working its way off the gears, or had "settled" at a position with the edge of the belt sticking out from the ends of the tensioner roller and cam gear (which was immediately after the tensioner).

In the end, I couldn't make sense of it so I guessed that there was something wrong with the new tensioner, took it all apart again and fitted the old tensioner. Resulting in the new belt running perfectly as it should.

Any thoughts??

[itcaptainslow]

Any play/movement in the bearings of the new tensioner?

I've had a cam belt "walk" off the pulleys on an MGF, which despite Brown & Gammon's insistence there was nothing wrong with the tensioner, there clearly was, thanks to the slight play in the bearings & roughness when spun up (I should have checked it prior to fitting really - lesson learned!). A fresh tensioner solved the issue.

[Panamax]

It's simply a question of where exactly the tension is in the belt.

If you put a rubber band round a bundle of sticks it's likely to be under more tension in some places than others. It's exactly the same when you put a new belt on an engine. However, on an engine the sticks can rotate (albeit stiffly) and the tension will even out through the length of the belt after a few rotations and and you'll get a proper tension reading. Much like running your finger round that bunch of sticks a few times under the elastic band.

[paul_c123]

itcaptainslow said:

Any play/movement in the bearings of the new tensioner?

I've had a cam belt "walk" off the pulleys on an MGF, which despite Brown & Gammon's insistence there was nothing wrong with the tensioner, there clearly was, thanks to the slight play in the bearings & roughness when spun up (I should have checked it prior to fitting really - lesson learned!). A fresh tensioner solved the issue.

Nothing obvious to the naked eye wrong with the new tensioner. I guess there is some kind of manufacturing defect and its not true/straight or whatever, and that can cause the belt to walk off the pulley. Doing a bit of Googling around, it does all start making sense.

[itcaptainslow]

paul_c123 said:

itcaptainslow said:

Any play/movement in the bearings of the new tensioner?

I've had a cam belt "walk" off the pulleys on an MGF, which despite Brown & Gammon's insistence there was nothing wrong with the tensioner, there clearly was, thanks to the slight play in the bearings & roughness when spun up (I should have checked it prior to fitting really - lesson learned!). A fresh tensioner solved the issue.

Nothing obvious to the naked eye wrong with the new tensioner. I guess there is some kind of manufacturing defect and its not true/straight or whatever, and that can cause the belt to walk off the pulley. Doing a bit of Googling around, it does all start making sense.

Hold it by the base in one hand, and try to wiggle the roller part with the other (if you haven't done this check already, not trying to teach you to suck eggs ). Play in the bearings won't be obvious by eye. Could also be not running quite true when fitted. Was it a genuine part?

[paul_c123]

Bearing is fine, its a Gates part.

[tux850]

paul_c123 said:

I guess there is some kind of manufacturing defect and its not true/straight or whatever, and that can cause the belt to walk off the pulley.

Yeah, it does sound like it, and whatever it is I imagine there's nothing you'd be able to do to resolve it (other than replacement of course).

[oakdale]

Sounds like the tensioner is not sitting flat on the block, is there a pin or tag to locate it?