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Chattering from timing belt of a 912 LC engine with semi-automatic tensioner - Engine & Ancilliaries/Gearbox - The Lotus Forums - Official Lotus Community Partner Jump to content


Chattering from timing belt of a 912 LC engine with semi-automatic tensioner

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After the timing belt was changed recently some kind of a rattling noise came up, which at first sounded like something concerning the exhaust. On closer inspection, it was then the timing belt, which strucks to the upper bracket of the cover in partial load operation. It can be seen fluttering properly. The TB is very tight between the cam gears and in direction to the semiautomatic tensioner it appears obviously something more free because of the movement of the tensioner.

I have now adjusted the screw on the tensioner. It is now better but still not good. However, there are also only 3-4 threads left ...

Do I need more or less purely turn the nut right until the end, or are the springs in the tensioner worn out and must be replaced? Or is it something completely different ?

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Is an OEM belt?   I once fitted a pattern part and is vibrated as described on overrun - even when tightened beyond spec.  I presume it was to do with different weight/density or whatever.  Anyway once replaced with an OEM belt it was fine.


Curiously, I've got a very similar issue at the mo.  Changed belt and weekend and to get to the correct tension, it is taking all the slack out of the semi automatic adjuster (if that makes sense) - i.e. The semi automatic adjuster effectively becomes a solid adjuster.  I ordered new springs yesterday, so I'll pop them in next weekend and report back - currently pondering whether I can remove tensioner while leaving belt etc in situ - looks do-able    

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Well the new springs have done the trick for me - now reaching correct tension with extra room to spare on the tensioner and its no longer taking all the 'spring loading' .  Pair of new springs approx. 10mm longer than old.   Tensioner easy to remove without disturbing belt - only needed to remove alternator.  Could even leave air con compressor in place 

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I seem to remember you just unwind the tensioner and it all springs out. Question is then is it possible to compress the spring and get the tensioner to wind in again without cross threading it in situe? This was possible using an old spring on mine but a new one might be a bit of a fight.

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It is possible, but involves much grunting with the risk of significant pain...

British Fart to Florida, Nude to New York, Dunce to Denmark, Numpty to Newfoundland.  And Shitfaced Silly Sod to Sweden.

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I thought about trying, but the aircon compressor would have meant you would need to feed everything back in at an angle  - It really is straightforward to remove the tensioner in situ -  Even on the bench it was fiddly putting the new springs back in. 


As Charles says, its just a case of unwinding the 'screw' until it comes apart - There are 2 concentric springs in there.  As a guess. I would reckon there is maybe 5-10 kilos of force to compress the spring to put it together, so remember it will want to try to fly apart too!

Edited by 910Esprit
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Hi Don - I think there is something slightly lost in translation....!   However this is procedure.  I only needed to remove alternator on esprit - may be easier on a front engine model? 


0.   Put engine to tdc and also wedge something suitable to make sure aux pulley can't move  (so the cambelt will stay in place when tensioner is off) - The belt will stay in place even with the tensioner removed

1.   Unscrew tensioner adjuster until 12mm thread showing (including the thread under the locknut)

2.   Identify which of the large 2 bolts, that secure the tensioner, is hiding the 4mm hole

3.   Remove that bolt leaving the other still secured

4.   deflect the belt between the aux pulley & inlet cam pulley to fully compress the tensioner & insert 3.5mm nail or similar in the 4mm hole  ( a suitable size masonry nail is ideal)

5.   remove the other securing bolt  (be careful not to stress earth lead from whichever bolt secures it)

6.   Remove tensioner to bench

7.   dismantle tensioner by continuing to undo tensioner screw (keep downward pressure while doing this as its under spring pressure)   use a towel or similar to avoid risk of injury

8.   Refurbish adjuster as appropriate 

8.   Replace 2 concentric springs.     

9.   Refit tensioner adjusting screw- a little tricky as you need to apply downward pressure as threading back in, but you'll do it after a couple of failed attempts!

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Excellent summary :) thank you.

For the translation: yes... There is always the chance that I mix the words wrong together :( So sorry for any unconvinience in that case.

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