Lotus Elan and Lotus Elan Plus 2 Forums

hi all
driving home yesterday started getting a bit of a knock from the engine.......
got home and tried the long screwdriver stethoscope which seemed to point to front of cylinder head...
doesn't sound like timing chain, but I could be [hopefully] wrong.....I suppose it could be any of a number of things ....cam bearing? cam follower? valve spring?...
whn it stops raining I will be removing cam cover to inspect.......any hints on what to look for?
I would be grateful for any pointers!!!
thanks in advance..

fred .

Is the knock at the frequency of the cams or the crank or neither? That helps narrow down what is the cause.

cheers
Rohan

hi rohan
thanks for your reply
it is a fairly high frequency.....
have looked at the cams/valve gear and all seems ok.... clearances are a bit more than book but all exhaust and inlet similar
play of timing chain about 1/2in between cam sprockets, but I have a question on that .....
the cam sprockets are relatively fixed with the pressure of the valve springs on the lobes so even with a load of slack around the rest of the chain would there be much more play between the cam sprockets?

I am beginning to suspect tensioner sprocket.........do they wear out often?. is it possible to remove the pivot pin and tension sprocket assembly without taking the head off?

fred

Yes it is. Set to No1 TDC with cam timing marks aligned, slacken tensioner, undo cam sprockets and remove. Slacken tensioner pin, grasp the tensioner with long nosed pliers, remove the tensioner pin and remove tensioner sprocket assembly.

I haven't changed my idler sprocket in 270,000 miles and I can't see why it would induce a knock. I assume you have tightened the chain since the knock started as they do stretch over time, allowing the cams to clatter. I tighten until it starts whining and then back off a little as I find the up/down measurement is too vague to rely on.

Not sure what you are hearing, but if it's a rather hard knock that gets worse with speed, it could be a rod bearing. If you pull the plug wire from that cyl and the knock stops that would indicate that it probably is a rod bearing.

well, could it be something as simple as adjusting/tightening tensioner?

yes it could!

thanks for all the replies!

btw valve clearances were around 0.027 [ex] and 0.017 [inl] ..
I appreciate this is well over book settings, but won't do any harm apart from a bit down on power, and a bit rattly when cold....
is it worth re-shimming to correct clearances, or leave it for a winter job? [I use the car every week]

those valve clearances will give a lot of tapping noise but I presume your knock is a deeper and heavier noise at the nose and not distributed along the cam cover

cheers
Rohan

hi rohan

as posted above I adjusted tensioner and knock has gone.......
I will probably replace timing chain and adjust valve clearances over the winter....I can at the same time check if tensioner sprocket/bolt/bearing needs replacing......

what's your opinion on split link timing chain [not racing!!]

thanks for your help!

fred

I have used a split link chain for a number of years in a racing engine I did not want to pull down so I don't see any real problem in using one in a road engine. Not my preference but it is not an unacceptable real world compromise

Just make sure the chain itself is a good quality solid roller chain and that the removable link clip has its open end facing backwards from the direction of chain travel.

The adjuster sprocket does wear and bend so they run at an angle to the chain so they do need replacing.

cheers
Rohan

Hi Fred

I agree with Rohan, just fitted a new split link chain to stop clatter of a stretched chain.
A new solid chain will be fitted next time the front cover comes off, hope that's not to soon.
Make sure you attach a good strong cord for the pull through.

Good luck

Fred,
I think you've been using metric feeler gauges measuring in 0.01 mm steps to get 0.027 and 0.017 gaps. In inches these would be 0.0106" and 0.0067", on the money. If they really were 0.001" measurements it would sound like a diesel and you wouldn't have noticed the knocking!