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Twin Cam Timing Chain Adjustment

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RobT

RobT

Jedi Warrior
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So here's another silly beginner question from a new owner of a TCS Lotus Europa.

I have only had the car a couple of monts so am still finding my way around and de-bugging odds and ends. Well I have noticed that at idle(900rpm or there abouts)there is quite a bit of clatter comming from the engine. Reve it up a bit (say 2,000rpm) and the clatter goes away.

So I conclude it could be a loose timing chain. Now I do the right thing, and read the workshop manual - which indicates there is an adjustable timing chain tensioner (yipee!). The manual goes on to say that the tensioner should be adjusted till any noise is eliminated (yipee #2).

Well I backed -off the lock nut and gave the tension adjustor a couple of turns, and indeed it does seem quieter.

But my question is, is there a more specific technique to adjusting the chain tensioner? How much should I adjust it, and do I risk over-tensioning the chain? And how much exposed thread on the tension adjuster is considered "normal"?

As usual, I am most appreciative of any advice.

Rob.
 
I always just went by feel - tight enough to be quiet but not much more than that, just a little tension. I'm not sure what's considered "normal" - as long as there's enough thread visible to indicate there's some adjustment left I wouldn't worry if there are no symptoms of a loose chain.
 
I'm such a fuss... Remove the cam cover, tension the chain to allow no more than a half inch of deflection between the cam cogs, no less... And look for evidence of "scarring" on the inside top of the cover. If you've not been under there yet you may want to have a cover gasket in-hand. No tellin' if the one on it was glued or not. That would also be a good time to run some feeler gauges between the cams and buckets.
 
Yes - I know. I should really pull the valve cover off and do it properly. Was just hoping there was a "lazy man's" technique for adjusting the tension without going to the trouble of pulling a bunch of (so far leak-free) parts off. But guess I should know better.

Rob.
 
They can be made/kept free of leaks. Attention to detail is the only "secret."

You've not posted engine bay pix... are the "crossover pipes" still in place? They can be shed shelf items with no detriment to the running of the engine. Blanking plates to cover the ports (aluminum & Nylok nuts look good). That way the NEXT time the cover needs removing it's a LOT less messin': eight nuts and away.
 
I'm more used to the TR250 cover which has just two bolts and always leaks (although mine dosen't any more thanks to a silicone gasket!) But the Lotus cover looks a lot stiffer and easier to torque down so as not to leak. Lots of cork and gasket goop to scrape off though!

I don't have the cross-over tubes - the car has extractors in place of the stock exhaust manifold. There are blanking plates on the intake manifold - home made jobs that look real ugly. I do have the "catch tank" still installed though. What the heck is the use of that?

Rob.
 
meh... umm... "esthetics"? /bcforum/images/%%GRAEMLIN_URL%%/jester.gif

The cover is cast alloy so it'll keep its seal well if done right. There are some rubber coated washers under each nut to seal those well, too. The li'l "half-moon" rubber blanks are the "usual suspects" for leaks. The other culprit is a short, squat rubber 'downtube' between head and block... we don't wanna even go there just now, tho. /bcforum/images/%%GRAEMLIN_URL%%/smirk.gif

You can read more on that thing in the thread Curtis started, below.
 
Thanks Doc.

Read the Curtis thread - and indeed hope I don't have to go there!

Rob.
 
"YEAH, but it's a SLOW leak." /bcforum/images/%%GRAEMLIN_URL%%/laugh.gif
 
Yup. You're correct!

What's my percentage? :jester:

A real "quick-n-dirty" way to ascertain rotation direction is to see where the chain tensioner is located. The side it's on will be the "slack" side of the chain. :wink:
 
Well since I started this thread - thought it time for an update.

I pulled the cam cover, and tensioned the chain per the book, also checked the valve clearances - all good.

Also reinstalled a mechanical fuel pump, had the carbs and dizzy rebuilt, brakes rebuilt, all new lines, rear end rebuilt with AVO shocks, starter motor rebuilt, etc, etc, etc.

Now the car goes like a bomb!

I did have oil leaking from the down-tube between the head and the block. Through ignorance (and there not being anything in the book about it), I just pulled the tube out (its pretty easy to get to on the Europa) put HT RTV silicone around the top and base, and reinstalled. Seems good.

There is still some oil leaking - looks like its going up the dizzy shaft and out the weep hole. Would this indicate a bad seal, or just too much crankcase pressure. Wondering if a PCV valve/hook-up would cure this (and any other) leaks.

Rob.
 
You should have a tube at the rear of the head which goes into the air filter box to create a slight "draw" on the crankcase. The seals for it may be allowing less than optimum vacuum? As for the dizzy, it should have an O-ring seal, maybe a smaller (ill-fitting) one was fitted when it was redone?

Both are WAG's at what you describe, but it's a starting point.

I'm impressed you could get that drain tube back in place and sealed. Must be a relatively new one. They usually go to pieces when wrestled out of there. :thumbsup:
 
Yes, the dizzy has an o-ring in the recessed groove on the shaft where it goes into the block - actually I added a second at the top of the shaft just below the clamp to add some extra "sealing power". But the leak seems to be from inside the dizzy - I think the oil is finding its way up inside the body of the distributor.

Also the tube from the head to the air box is installed and seems fine. Was thinking this may not give enough -ve pressure to the crank case though. Hence the PCV idea.

I guess I was lucky with the drain tube! But rather be lucky than smart any day :yesnod:
 
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