T/C Timing chain tensioner

[richardl46]

Head back on today but having problems with chain adjustment......

Only 5 mm of adjusting screw showing (when 1/2" vertical movement between cams sprockets) so can't get locking nut on and no room for wear.

I understand the head was skimmed to raise the compression ratio to 10.5:1 back in the 80's when the engine was worked on by Vulcan Engineering. Surely this would not affect the tension significantly?

A new standard 120 link chain has been fitted. Also a new tensioner spring and plunger.

The Lotus workshop manual (and attached e-bay advert) appears to show a collar on the end of the tensioner screw, which would extend the screw and prevent it tending to open up the spring. Others illustrations show just the screw acting directly on the spring, which mine has.

Burton offer a 46 mm plunger instead of the standard 36 mm which will help, but doesn't explain why I have this situation.

Any advice would be appreciated.

[promotor]

The only issues I can think of is the block could have been skimmed aswell as the head, or you have a tall block conversion. What are the numbers on the cylinder block?

Are you saying your tensioner looks like the one in the picture except for the thrust washer on the end? That looks like the biggest culprit.

[richardl46]

The block is marked 701M 6015 EA on one side then the individual number P32534 on the other.

I've no idea if the block has been skimmed as well as the head.

If the tensioner screw should always have a washer retained at the end then I will replace that, even before trying the longer plunger. It's quite possible the screw is burying itself inside the spring, but it is always detached when dismantled.

I've counted the links to confirm 120 and the chain must be fully around both lower sprockets as it's turning over normally.

The engine is in a 1972 Lotus Seven Series 4, but was a substitute for the original 1500 GT engine, so could have come from an Elan or Ford.

Thanks for responding.

[billwill]

If you push it in TOO far the chain will grind chunks out of the water-pump boss.

It may be that your head to crank distance has been reduced so much that you will need to get a 119 link chain, which of course implies a special build with a cranked link.

[john.p.clegg]

Richard
And that should be dead-easy for you ( living in Notts ) as there is a guy who makes up chains at most Newark jumbles...had mine or years and am a happy bunny.

John

[promotor]

The block is marked 701M 6015 EA on one side then the individual number P32534 on the other.

I've no idea if the block has been skimmed as well as the head.

If the tensioner screw should always have a washer retained at the end then I will replace that, even before trying the longer plunger. It's quite possible the screw is burying itself inside the spring, but it is always detached when dismantled.

I've counted the links to confirm 120 and the chain must be fully around both lower sprockets as it's turning over normally.

The engine is in a 1972 Lotus Seven Series 4, but was a substitute for the original 1500 GT engine, so could have come from an Elan or Ford.

Thanks for responding.

OK - 701M block is proper Lotus height block so that's one less thing to worry about. The threaded rod comes with a nipple and a washer - you have to peen the nipple over to retain the washer whilst still allowing the washer to rotate.
Does the brass timing chain tensioner have any wear to where the plunger contacts it? If so that would require you to have the adjuster wound in more.

[Hawksfield]

Richard

You certainly require the washer on the adjustment rod, has it got a spigot without a washer ?

I would sort this first and try again

[holywood3645]

Agree with previous comments on washer. I chased that for a long time during my rebuild. It kept jumping teeth
James

I don't think it's related to a tight timing chain however

[richardl46]

Nipped over to QED and got the washer. All now so obvious I must have experienced a senior moment !

I'm also surprised to find the washer acting directly on to the plunger, with the spring just acting as a damper. The spring projects barely 5 mm out of the plunger but I assume this is correct.

The idler arm has very little wear on the heel. Now I have the correct tensioner set-up the adjusting screw is projecting about 22 mm beyond the face of the large nut, when the chain has 1/2" of play.

Many thanks for all the helpful advice. I can crack on now ........until the next senior moment !

Richard

[holywood3645]

You are not the first to miss this... Gaud knows I spent hours trying to figure it out.
James