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Cambelt tensioner: replacing piston


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I'm probably going to buy the cambelt tensioner overhaul kit for when i replace the timing belt on my Lotus Eclat. But I'm just looking for a bit of clarity regarding replacing the piston. The factory manual talks about the locking pin going through the groove of the piston, saying "The pin is inserted to prevent the springs pushing the assembly apart and consequently losing all the parts... Do not under any circumstances attempt to remove locking pin from the tensioner assembly, other than when unit is installed on an engine with timing belt in position".

So how would I go about switching out the piston if that's the case?

SJ510.jpg.e92faad13637ac206ac85483284b629a.jpg

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While rebuilding the semi-auto tensioner, you can (have to) remove the locking pin. Do unwind the adjusting "bolt" rather than just pulling the pin and watching bits fly across the workshop, and when rebuilding, get the piston locked by the pin then insert the adjustment "bolt" .

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Dave,

Just checking that you know the tensioners are not all the same before you go spend money. Check whats on your car first before buying the overhaul kit. I think a '79 probably is the spring loaded arrangement, but best to check. I actually prefer the earlier (and later) eccentric hub tensioners. - simple and effective. Setting the tension correctly is harder though.

Dunc

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  • 2 weeks later...

This is one of those jobs where I always reach for some eye protection. The first one I ever dismantled had a very worn and soft piston and even though the locking pin was fitted it managed to suddenly appear with the spring bunched up behind it. Also a friend had one go when loosening the spring tension - the end of the threaded sleeve sheared off whistling past his ear.

 

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Thanks for the advice. So the plan seems to be:

  • Eye protection on
  • Remove adjuster screw until locking pin/drill bit can be put in place
  • Once pin in place, remove tensioner from car
  • Carefully unscrew adjusting screw, while trying to keep inward pressure on it so it doesn't fly across the room when free
  • Remove adjusting screw and pull out spring behind it
  • Remove locking pin
  • Remove piston out of hole at front

Could someone just confirm that, especially the point at which I need to remove the locking pin?

Two more questions for now:

  1. SJS have two springs listed ("inner" and "outer"). Are both of these between the adjusting screw and piston?
  2. Am I right in thinking the piston comes out of the adjusting screw end of the tensioner, or out of the front?

Sorry for the dumb questions but am just trying to get my head around things before I actually do it.

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Bullet 2 - 'unscrew' (but not remove) to insert pin ( no more that 12mm of thread exposed).    Insert the pin by deflecting the belt by hand to push the piston so the pin hole aligns with the slot in the piston.      Once removed from car, just wrap in towel and fully remove screw.    I assume you also know that the securing pin hole is obscured by one of the tensioner mounting screws?

two springs are just concentric inside the device.   NB you are probably overthining this.  Its a very basic mechanism (a tube with a screw at one end and a piston at the other, with a spring in between)  .   You could just unscrew the screw in situ with a towel in place until it explodes, replace the springs and reassemble!! - Springs are not that strong!   

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9 hours ago, soldave said:

Thanks for that Dunc. Finally got around to taking a picture and by the looks of it I have the spring loaded tensioner.5a0f6f02df000_2017-11-1722_29_41.jpg.60b771ad171a043afa952753d7d88445.jpg

Dave, your reconditioned tensioner was fitted about 6 months before you bought Banana. Just for your records.

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12 minutes ago, johnpwalsh said:

Dave, your reconditioned tensioner was fitted about 6 months before you bought Banana. Just for your records.

Very handy to know, thank you! In that case I may just get the tensioner bearing :)

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Slow and steady was the progress today Decided to take the tensioner and bearing off to take a look at them. Both look in decent condition and no sound from the bearing so am pretty pleased with that. Spring and piston seem good too although now of course I can't get the adjusting screw pushed back into the tensioner body! Tried using all of my weak powers and can just about push the adusting screw to the body but can't get it to turn and bite. Am away from tomorrow until next weekend so will get a garage to help me next Saturday - should be a simple job. The week also gives me time to order some new coolant, as well as a power steering and fanbelt. May as well replace those while things are off.

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