Lotus Elan

Timing chain rattle-- strange tensioner issue

PostPost by: elaninfuture » Tue Jan 15, 2019 4:57 am

I noticed a slight (and sudden) rattling sound as I was working on my car. It hasn't been on the road since the '80s, so no real surprise.

I pulled the cam cover to have a look. I noticed that the timing chain on the tensioner side was awfully close to the cylinder head.

With a long flat (and clean) screwdriver, I was able to move the chain tension sprocket about 1/4 inch laterally, which put the chain in a more proper position. I turned the engine over several times. The sprocket appears to stay in that position.

However, with a screwdriver, I am also able to push the sprocket back into the previous position (the one in which the chain appears to be too close to the head).

I have the workshop manual, but I'm confused as to the problem. Does the sprocket bushing (#17 in workshop manual-Key to camshaft and valve mechanism) go bad allowing lateral movement? Or is my problem more likely a movement of the tensioner bracket?

Is the entire assembly (tensioner, sprocket and bracket) available, and is it possible to change without removing the cover?

I also noticed the chain is tighter than 1/2 inch in deflection. More like 1/4 inch, and that with much pressure.

As I'm sure you can see by the question, I'm new to Lotus. All advice much appreciated.

Good news is the car seems to run great.

Joe
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PostPost by: rgh0 » Tue Jan 15, 2019 8:16 am

The sprocket bushing can wear and the swing arm can be bent by twisting especially if the chain is over tightened. Both these can result in lateral wobble movement of the pensioner sprocket and bring the chain close to the head.

If you remove the inlet cam sprocket you can then remove the tensioner pivot bolt and lift it out for inspection and replacement. I don't think the tensioner fits down the gap to fall into the sump if you drop it but I would be careful to tie a wire around it so it can be lifted out before removing the pivot bolt.

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PostPost by: elaninfuture » Tue Jan 15, 2019 3:40 pm

Thank you, Rohan. That's helpful. I'll do it.

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PostPost by: elaninfuture » Thu Jan 24, 2019 3:58 am

On further investigation, I've been able to determine that the tensioner bracket is fine (at least it appears so). Same with the chain tension sprocket.

The lateral movement is of the entire unit (bracket). It moves laterally on the pivot pin. When pushed toward the head, it moves the chain so that it's nearly touching the metal, which I think is what's causing the rattle.

Is the bracket meant to move laterally on the pin? In the workshop manual, I see nothing (bushing or such) to keep it from moving, so I imagine this is the way it's mean to be?
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PostPost by: Craven » Thu Jan 24, 2019 11:26 am

Arrangement should be self-aligning, as you will realise the sprocket on the camshaft in the block and the sprocket on the inlet camshaft in the head are not in a fixed relative position.
I have seen engines where the alignment is so bad the backside of the adjustment sprocket has been chewed away, it?s possible you have a case of poor alignment and you are at the limit of the self -aligning action, so look for aggressive chain action on the sprocket.
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PostPost by: elaninfuture » Thu Jan 24, 2019 3:45 pm

Craven wrote: so look for aggressive chain action on the sprocket.


Thanks, Craven. What do you mean by "agressive chain action on the sprocket?" You are referring to the sprocket on the tensioner, correct?
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PostPost by: Craven » Thu Jan 24, 2019 4:14 pm

The brass quadrant floats on its pin taking up a position dictated by the run of the chain, checking to see if the chain is forcing the quadrant over to one side when running may be indicated by heavy scuffing on one side, Yes, the sprocket on the adjuster quadrant.
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PostPost by: Quart Meg Miles » Thu Jan 24, 2019 5:45 pm

The head is not securly located fore-and-aft and I once rebuilt the engine and found the chain badly fouled the timing case on the left block side. The noise was awful but your chain's proximity may be due to the head position.

Are you sure the rattling noise isn't just the oil warming up and letting out the normal timing chain sound or flushing years of gunge out?
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PostPost by: elaninfuture » Thu Jan 24, 2019 6:18 pm

Thank you. I'll check it out. I don't think the noise is the normal sound of warming up, although I wouldn't know as this is my first Lotus. My twin-cam Alfa does not make a similar noise.

Also, I can see a slight groove worn where the head meets the block, at the spot where the chain passes (intake cam side). The chain, however, displays no signs of wear on the links, so perhaps this groove was worn long ago.
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PostPost by: 2cams70 » Thu Jan 24, 2019 9:44 pm

If the car has been out of action for a long time it's possible that the tensioner plunger is sticking in its
bore due to gummed up varnish or there's something wrong with the tension spring. I'd remove the chain adjuster assembly nut and check that the plunger is free to move and spring ok.
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PostPost by: nmauduit » Fri Jan 25, 2019 9:25 am

elaninfuture wrote:Also, I can see a slight groove worn where the head meets the block, at the spot where the chain passes (intake cam side). The chain, however, displays no signs of wear on the links, so perhaps this groove was worn long ago.

if you want to check that out, you may be able to clean the area of the purported contact and ink it generously with a sharpie pen, run it a bit (if you wait too long the oil will wash the ink away) and check again the contact area vs the immediate inked surrounding for contact marks.

Traces might also be found in the oil (filtering it through a coffee paper), though if very small actual provenance would be difficult to pin point.
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PostPost by: john.p.clegg » Fri Jan 25, 2019 10:12 am

"The head is not securly located fore-and-aft " ?

I had big bolts in mine...

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PostPost by: john.p.clegg » Fri Jan 25, 2019 10:16 am

The brass tensioner quadrant can get twisted if mis-treated,forcing the chain fore or aft..

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PostPost by: englishmaninwales » Fri Jan 25, 2019 9:43 pm

john.p.clegg wrote:"The head is not securly located fore-and-aft " ?

I had big bolts in mine...

John :wink:


But no dowel location.....
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PostPost by: Foxie » Sat Jan 26, 2019 12:55 am

englishmaninwales wrote:
john.p.clegg wrote:"The head is not securly located fore-and-aft " ?

I had big bolts in mine...

John :wink:


But no dowel location.....


I presume you are talking about the head stud holes being considerably wider than the bolts/studs, allowing the head to move around when refitting.

I use ARP bolts for the cylinder head, but when I am refitting the head I use two of the original studs in the block, one at the front and one at the back, to guide the head into place. I have prepared the studs by winding a tapered wrapping of insulating tape at the base, which is a close fit in the head bolt/stud holes. This first fixes the gasket position, and then the head position when it is lowered down. The head is then anchored by fitting and lightly tightening a few bolts before removing the two studs.

Similar tapered locating studs but more durable could be machined up from steel to perform the same function. :)
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