Lotus Elan

Changes in Valve Clearance

PostPost by: Gardog » Thu Jun 08, 2017 4:05 pm

I am hoping that one of you experienced Elan owners may be able to shed some light on a problem I have discovered with my valve clearances.

My engine was rebuilt 2000 miles ago by a reputable engine shop. Valve clearances were set to spec.

Two weeks ago the car overheated (stuck thermostat). I was able to shut down quickly and a subsequent inspection showed none of the problems normally associated with a head gasket failure. I noticed however, that the engine seemed to be making more tappet noise than before so I checked valve clearances

The exhaust valve clearances were 12 to 21 thou. The intake valve clearances were all less the 1.5 thou.

I don't know for sure that overheating is at the root of the issue. The engine may have been getting gradually noisier before the overheating. In any case, I would like to understand what caused the changes before I take the time to re-shim all of the valves.

Does anyone have any thoughts or similar experiences?

Gary
Gardog
New-tral
 
Posts: 14
Joined: 24 Feb 2017
Location: Vancouver, Canada

PostPost by: nigelrbfurness » Fri Jun 09, 2017 9:22 am

Gary, I can't personally see how overheating can be the cause of your problem. I've had twin-cam engines that boiled, thrown rods and other disastrous events and the valve clearances have not been affected. I've had engines that have done 40K miles with barely measurable changes in the valve clearances. The most likely cause is that they were not set correctly for some reason at your engine rebuild so should be done now. Closed up clearances are usually caused by excessive valve seat wear or the occasional soft shim. If your inlet valves have some clearance then the engine will have run reasonably and I doubt there will have been any valve damage. Exhaust valves that are open too long (clearance too small) will burn after a while, maybe not in 2000 miles though. >12 thou clearance will be noisy but probably not cause any serious damage.

If you find that you are needing to use very thin shims ( < 60 thou ) then you might consider pulling the head to look at the valve seats, they may have been cut too deep or your head over-skimmed. It is dangerous to generalise with these engines but shims around 130-160 thou usually indicate plenty of life left.

Valve clearances should always be checked cold - I like to wait about 12 hours after the last run.

I would just go through them and set them all correctly and hope for the best!

Nigel F.
1970 S4SE/1760cc big valve/SA-AX block, L2s, 45DCOEs, 1978 Jensen GT, 1962 AH Sprite, Alfa-Romeo 159, 1966 Bristol Bus, 1947 AEC Regal bus.
nigelrbfurness
Third Gear
Third Gear
 
Posts: 398
Joined: 04 Apr 2008
Location: Dunmow, Essex, UK

PostPost by: Gardog » Wed Aug 09, 2017 2:49 am

I have discovered the cause.

The cam bearings on the exhaust side were damaged when the car overheated. I have replaced them and the valve clearances are back to spec.

The inlet valves are also within spec. I had not rotated the cam lobes quite far enough when I measured the first time.

Gary
Gardog
New-tral
 
Posts: 14
Joined: 24 Feb 2017
Location: Vancouver, Canada

Total Online:

Users browsing this forum: No registered users and 6 guests