Cambelt tension


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t3gav

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Nov 10, 2011
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How much movement is generally accepted on the cambelt. I have a new cambelt and tensioner but because my head has been skimmed a little the belt obviously isn't as tight as before, I can turn the belt almost 90deg in the middle of the longest section. It's tensioned as per the manual i.e. turn cam gear 3 degrees and torque tensioner bolt. Thanks
 
Head being skimmed won't make a difference to tension,tensioner will take up the slack as normal, perhaps your spring has gone a bit weak
 
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Just to add if your head has been skimmed a lot you should use vernier pulleys to maintain correct cam timing
 
If the head is skimmed the cam pulleys are closer to the crank so the belt is effectively longer, when correctly adjusted the belt is still too slack as the belt is too long, I can tighten the tensioner more using the 'screwdriver' technique but this is a pain with the engine in the car as you can't get to the tensioner. I have vernier pulleys :) this is quite a common problem especially with lairy cams with more drastic ramp angles etc as the belt slaps more.
 
t3gav said:
If the head is skimmed the cam pulleys are closer to the crank so the belt is effectively longer, when correctly adjusted the belt is still too slack as the belt is too long, I can tighten the tensioner more using the 'screwdriver' technique but this is a pain with the engine in the car as you can't get to the tensioner. I have vernier pulleys :) this is quite a common problem especially with lairy cams with more drastic ramp angles etc as the belt slaps more.
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I don't think you understand the principal of what I'm saying,

If the head is skimmed then it will have the same effect as a longer belt, yes your right,

So then the job of the tensioner is to pull the extra length of the belt up and in at the back, but when you do this the crank has to turn counter clockwise slightly to remove the slack,making the cam timing out hence the need for adjustable cam pulleys.

That endyne part is more a guide to stop deflection, it has nothing to do with taking up slack from incorrectly adjusted belts
 
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That's the problem though, with a longer belt the standard tensioner will spring to it's position and not provide the same tension it would on a shorter belt. I think I'll just have to pull the tensioner up a little more than the spring does normally. I've heard of people doing this and galling the cam journals but that's because they try to get 'extra' tension to stop belt slack caused by mega high lift cams. My belt/tensioner is new btw.
 
If your going to try and get extra tension then just remember that cam belts tend to tighten up a bit when the engine is up to temp due to expansion
 
Sorry yeah I understand what you're saying about the cam timing now. I degreed the cams with the belt set at the tension it's at now, does my belt tension sound about right as it is?
 
Did you degree them to the spec given by the manufactures?

Best way to check tension is by measuring the diflection ( distance it moves from being pushed Right back to being pulled forwards) hope that makes sense??

Think it should be up to about an inch but I could be wrong so best look it up
 
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b16 mini said:
If your going to try and get extra tension then just remember that cam belts tend to tighten up a bit when the engine is up to temp due to expansion
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one very smart remark.
i totally agree,most important look at the timing marks.
on camgears and crankgear, Not the pulley.
and skimming a head wont take much material of.
 
To be honest I tedn to give the tensioners a little pull by hand when fitting new belts, adds a bit of tension. Don't go too mad though :)
 
As above give the tensioner a little pull to achieve the right tension. The problem your having is pretty common on engines that have had a head skim or block decked.
 
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