Lotus Elan

timing chain tensioner

PostPost by: potleyu18 » Wed Jul 17, 2019 9:08 am

Strange one, but has anyone changed the tension-er with the engine it situ and without dismantling the engine as it looks like I've over tension-ed it and damaged the rubber section?

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PostPost by: types26/36 » Wed Jul 17, 2019 9:35 am

If you are talking about the brass quadrant & gear then yes you can change it but if you are refering to the slipper on the exh side you would need to remove the front cover as the screws go in from the inside.
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PostPost by: 512BB » Thu Jul 18, 2019 8:24 am

Steve

Curious as to why you think you have damaged the rubber & steel slap pad. To view it, you must have removed the cam cover, to reveal what? If it has been scored or has lines down it, they could only have been made by the chain being to loose, not tight, slapping against rubber on over run I would think, hence the name. If it does that, it can also wear chain grooves on the underside of the cam cover as well.

A twincam engine makes a kind of screeching noise if the chain is to tight, difficult to describle noises, I find.

As my good friend Mr G points out, you did not know that Brian, did you :D chain tensioner removal and replacement can be done with just the cam cover removed. Tricky, but very doable. We do not want you to come back and tell us you had butter fingers that day Steve :lol:

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PostPost by: 69S4 » Thu Jul 18, 2019 9:38 am

There's not a lot of info about the rubber 'slap pad' in either the workshop manual or the TC Engine book. It tends to be one of those things that's screwed into place and left alone. A lot of 70's Japanese motorcycles use similar items as cam chain guides and tensioners and with those the chain is supposed to 'cut' two grooves into the material so that the rollers then run on the high area between them. So two grooves down the length of the strip is normal. I've never been sure whether the TC uses a similar approach or whether it's just there to save the casing from the consequences of a slack chain so normally wouldn't be in direct contact.
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PostPost by: Craven » Thu Jul 18, 2019 10:28 am

My experience would say, impossible to change this part without separating the front covers. It’s attached by two screws at right angles to the plate.
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PostPost by: types26/36 » Thu Jul 18, 2019 6:28 pm

Craven wrote:My experience would say, impossible to change this part without separating the front covers. It’s attached by two screws at right angles to the plate.

....and usually loc-tighted in and often peened over.
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PostPost by: types26/36 » Thu Jul 18, 2019 6:45 pm

512BB wrote: you did not know that Brian, did you :D chain tensioner removal and replacement can be done with just the cam cover removed. Tricky, but very doable Leslie

Not quite understanding you there my good friend Leslie :?: are you saying I did not know you can remove the quadrant and gear by taking off the cam cover, chain and backing off the adjuster? if so read my first reply as I have done it many many times and I dont regard it as very tricky but I suppose its what your definition of "Tricky" is :lol:
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PostPost by: 512BB » Fri Jul 19, 2019 7:25 am

69S4 wrote 'or whether it's just there to save the casing from the consequences of a slack chain so normally wouldn't be in direct contact'

That is correct Stuart. There is very little space where the timing chain slips between the water pump and the inside of the front cover so if there was no slap pad, a slack chain would just wear away the cover, but because there is, it just rubs on the rubber, a replaceable item.

Types 26 / 36 wrote 'Not quite understanding you there my good friend Leslie ?: are you saying I did not know you can remove the quadrant and gear by taking off the cam cover, chain and backing off the adjuster?

No, my good friend, I was not saying that, but I think this one has gone over your head, so we will move on. And answer the phone when I call next time, make sure you are in, all the time. :D

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PostPost by: 69S4 » Fri Jul 19, 2019 7:48 am

512BB wrote:69S4 wrote 'or whether it's just there to save the casing from the consequences of a slack chain so normally wouldn't be in direct contact'

That is correct Stuart. There is very little space where the timing chain slips between the water pump and the inside of the front cover so if there was no slap pad, a slack chain would just wear away the cover, but because there is, it just rubs on the rubber, a replaceable item.

Leslie


Having not paid much attention to how the pad functions in the past (making sure the screws are tight enough has been about it), I don't know whether the chain is meant to be in constant contact with the pad or not. If it is it will wear two grooves as deep as the height difference between the chain side plates and the rollers. That's how the Japanese bike ones work. By doing that they also damp down chain oscillation, something I would have thought the long run on the TC chain would be prone to if the tension isn't correct. If it's not meant to run in contact and the pad's only there as a last line of defence then presumably a correctly tensioned chain (!) should leave the pad unmarked.
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PostPost by: 512BB » Fri Jul 19, 2019 9:06 am

69S4 wrote ' If it's not meant to run in contact and the pad's only there as a last line of defence then presumably a correctly tensioned chain (!) should leave the pad unmarked'

That is correct Stuart. If it was in contact all the time, it would wear it away in short order. I rebuilt one of my engines last year, it having covered 40k miles. There were no marks on the slap pad and therefore I reused it, and the chain !, the timing chain obviously having been tensioned correctly throughtout those 40k miles :roll:

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PostPost by: 69S4 » Fri Jul 19, 2019 9:44 am

512BB wrote:69S4 wrote ' If it's not meant to run in contact and the pad's only there as a last line of defence then presumably a correctly tensioned chain (!) should leave the pad unmarked'

That is correct Stuart. If it was in contact all the time, it would wear it away in short order. I rebuilt one of my engines last year, it having covered 40k miles. There were no marks on the slap pad and therefore I reused it, and the chain !, the timing chain obviously having been tensioned correctly throughtout those 40k miles :roll:

Leslie


OK, so the marks on mine are more an indictment of my maintenance schedule than a statement of the designers intent. :lol: I got through a few of the Japanese bike ones before I realised they were meant to have the grooves. Different philosophies, different designs
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