Timing belt tension

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Timing belt tension

Post by Eightpot on Sun Aug 10, 2014 1:22 pm

...or the checking thereof.

The manual states the belt after settling by rotation should be 8-16n while being deflected by 5mm - so far so good. Except it's a bit of a struggle to get in the available space with a spring gauge and rule to measure.

How do others here set tension?  Is leaving it to the tensioner spring and fitting procedure enough or is it a thing you do by "feel"?  The last timing belt I fitted was on a Ford CVH (yep, that long ago) and to check tension on that was if you could twist the belt through 90 degrees it was correct.  Currently mines feels "not tight", but as far as I can see the gauge reads about 4lb at 5mm - but trying to read off the rule when the engine is lying on its side and with bugger all room, I think the margin of error is about half a housebrick.

Happy days.


Last edited by Eightpot on Sun Aug 10, 2014 1:25 pm; edited 1 time in total (Reason for editing : can type I)

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Re: Timing belt tension

Post by FrontBackSide2Side on Sun Aug 10, 2014 3:30 pm

I havent done one on a hijet but as a general rule of thumb that 90 degree method on the slackest part of the belt is the way i would do it without the tools to measure the tension etc.
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Re: Timing belt tension

Post by HighlyJetted on Sun Aug 10, 2014 4:24 pm

Bit tighter than too loose  - bit looser than too tight.

Make sure when you ping it you don't get a note from it!

A slight bit of deflection is good.

Needs to be tighter than the tensioner spring makes its.

But not so tight its going to nail the tensioner bearings or wear the camshaft.

90 degree technique is good, but it depends how strong you twist it!

I think on the whole, people tend to over tighten cam belts.
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Re: Timing belt tension

Post by Eightpot on Sun Aug 10, 2014 5:00 pm

Thanks for the replies.

I've done a bit of a hybrid tension technique: Started out using the manual as a baseline then giving the tensioner a bit of a tweek, rotating the engine and checking both with the spring gauge and a 90 degree twist.

And I have Woody's number ready in case the belt goes twang.

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Re: Timing belt tension

Post by HighlyJetted on Sun Aug 10, 2014 6:31 pm

Normally the tensioner bearings collapse, causing the belt to then break.
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