How tight is tight?

[Bison]

Folks,
No, I'm not referring to the fact that I'm a Scotsman!.
just fitted my new B spec cam belt to my Sport, it's really very tight, maybe 3mm max play, no way it would slide on like the belt does on my other sport, I had to "walk" it on turning the crank and pushing it and the crank pulley on at the same time. Normal?. I cleaned the grooves on both pulleys, as the bike has been off the road since around 1988 they were a bit mucky. If the cam belt on my car was that tight I would be concerned.
Thanks,
Alan.

[MickeyMoto]

A,B or C pulley?

[norbert]

If you ´ve got three mm play to me it sounds good. I always put the belts this way, if they are a bit tight.

[Bison]

B pulley.
Alan.

[EVguru]

I usually run an engine with the old belt for a short period to clean the pulleys.

If the belt isn't 'twanging' tight once on, you should be fine. A little talcum powder can help to slide a belt on.

[Bison]

Hi Paul,
I did start the bike for a second or two with the old belt on, but that was the first time since 19 oatcake it had been fired up, I would be concerned it would break, I'm sure as you say, the pulleys will clean up.
Alan.

[MickeyMoto]

I find belts tight on my B pulley, but once home have 3 or 4 mm movement at the testing point. Rather that than too slack, I presume? Also, being rubber would there be give in it, unlike a tight chain?

Max slack is only 6mm.

[EVguru]

The tension members in the belt have very little give. If you fitted a belt that was really too tight, then the rubber on the inside of the belt would be under compression as it ran round the pulleys. The would likely cause overheating and possible shedding of teeth.

Given the unique setup on a Morini where there is no tensioner, you would have to work quite hard to get a belt over-tight. Most engines have a spring loaded tensioner that sets the belt tension before being locked in place.

[mad muller]

just a word of caution on the tight belt , i fitted one on a new timing pulley from nlm , i had to force the belt on , very tight , engine ran like a dog , lots of probs its obvious after the event , that the new crank pulley had changed the tolerances the a b or c went out the window, had to try a few different belts till i got the right fit, snug is the word i would use, the guy at the local bearing shop give me a few to try , top bloke not a jobsworth, and bike ran fine , the overtight belt will in time knacker the cam bearing in fact i could here it , and causes to much drag on the engine, to slack can cause probs to ,just a thing to be aware of when changing timing pulleys. muller.

[Bison]

Thanks for the warning, I'll be checking it immediately after I've ran the engine. I think as Paul says once it's been run for a while the pulleys should clean up and give slightly more play. The pulleys are both the originals so it must have been ok when it left the factory, I assume!.
Alan.