Timing Chain! Any Wisdom?

[peter at rolotec.ch]

The slip pad is there to dampen (eliminate) chain vibrations on the part
between the driving crankshaft sprocket and the "first" (exhaust) camshaft
sprocket. Vibrations would spoil the exact camshaft timing. Normally the
chain passes just by the pad, it does not exert any substantial pressure. A
small gap does not hurt, but it should not get too big. (Who asks about a
figure in millimeters?) Nonetheless it is a good idea to replace the pad
when doing an engine rebuild. In my engine I saw two grooves from the chain,
about 1mm deep and experienced no ill effects.

Peter


----- Original Message -----
From: ElanS4 <[email protected]>
To: <[email protected]>
Sent: Thursday, September 02, 1999 2:58 PM
Subject: Re: [lotuselan] Timing Chain

[Foxie]

-----Original Message-----
From: Brian Martley <[email protected]>
To: [email protected] <[email protected]>
Date: 02 September 1999 06:29
Subject: Re: [lotuselan] Timing Chain! Any Wisdom?




When I got my Plus 2 back in 1985, I read about the dreaded split-link
chain. Problem is I have failed to find a source for a non-split-link
chain, and have replaced the chain twice in the intervening period (50,000
miles) with the split-link types. I have a Luminition rev limiter set at
7,000 rpm. Never had a problem.

When timing/removing/replacing cams to set cam clearances, I find that by
removing the tensioner assembly altogether, the chain can be slipped one
link at a time over the cam sprockets while judiciously rotating the
sprocket fractionally with a screwdriver levered through the sprocket slot.
Alternatively, unbolt and release the cam sprocket, refit the chain, and
"manouvre" the sprocket back on the cam, with a 5/8 spanner on the
crankshaft pulley bolt. (Remove the spark plugs to prevent loosening the
bolt in the reverse direction)

Do not rotate the crankshaft significant amounts (>10 crank degrees) in the
reverse direction with the tensioner removed, as the chain will slip on the
crankshaft sprocket and eventually cause piston/valve contact and lock-up.

I used to tie up the chain per some recommendations when removing the head
to keep it on the crankshaft sprocket, but now I just drop it on the water
pump casting, and recover it with a piece of bent wire when refitting the
head.

A good indication of chain wear is to "bend" the chain at right angles to
the links and compare with a new one. (Don't know how much "bend" warrants
renewal, though)

Hope this helps,

Sean Murray
Wexford
Ireland

1970 Plus 2S
Heading for Salzburg in the Plus 2 tomorrow !

[BrianMartley]

Richard and others,

The softening of the rubber on the slip pad is something I've also seen
before, it happened on a friend's engine rebuilt in the late 80s. We were a
bit puzzled at this, because the one on mine was years old, dating from at
least 1974 and the rubber was still hard.

I checked the rubber used on the new pad and found the hardness was quite
low for this application - we went back to our local dealer with whom we're
on friendly terms and checked out some others (quite easy - there's a
portable hardness meter for testing elastomers). We found they were all a
bit suspect, so Chris (the dealer) ordered some more, and they were much
better. We could only put it down to a poor batch - Lotus were out-sourcing
many parts at the time and maybe quality control wasn't so good.

At the time it was the only failure Chris had seen, but we reckoned that
most owners wouldn't use their elans daily, most were on limited mileage
insurance policies so it would take 3 or 4 years to get up to 10K miles.
Interestingly enough, if you have the Miles Wilkins book on the TC engine,
he mentions faulty slip pad rubber as a one-time problem area, which
re-assured me that it wasn't just "our problem".

Brian

[BrianMartley]

Peter,

Yes you're right in your assumption, although having a spilt link isn't a
requirement of the "holding with string" method.

I've also heard about links coming apart, it's entered folklore now, but I'm
not convinced that it's a fault of the split link itself. The chain on my TC
has been a split link since 1974, although it's not the same one

I think the important thing is to renew these chains as they start to wear -
although they seem pretty good as they run in an oil bath - because any
slight play or slackness will cause problems with a split link. I believe
the horror tales come from chains which are either loose, worn or have the
link incorrectly installed - the open end should trail the direction of
movement.

If the chain is correctly tensioned, all the loading on the link should be a
direct tension and the spring clip will see no loading. If the chain is
loose either due to incorrect tension or wear, and allowed to whip at high
revs, then it's possible to put a slight sideways loading on the links which
is not what split links are designed to take - hence the clip will spring
off.....

Brian