Lotus Elan

Oil fouling #1 spark plug

PostPost by: Davidb » Mon Nov 20, 2023 11:16 pm

Forgive me if this has been covered elsewhere--I just went back through ten pages and couldn't find any info although I do recall it mentioned . It was helped by fitting BP5ES plug in #1 cylinder as I recall seeing suggested on this site.
My engine has newish valve guides. I replaced the head gasket with a Cometic item not that long ago.
The most likely culprit is the oil feed to the camshafts passing through the head gasket of course. On other engines:- BMC A and B series for instance I have cured this by fitting a drilled dowel that sticks into the head and then fit an 'O' ring around it. You can't do that on a Twin Cam engine of course. Any suggestions?

As an aside, I am currently overhauling an Alfa 2600 engine for fitting in a special I have been working on for far too long. It has no less than 8 (eight) oil feed pipes going through the valve cover gasket! Each with an 'O'' ring of course...
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PostPost by: rgh0 » Mon Nov 20, 2023 11:55 pm

What type of Cometic gasket did you fit ?

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PostPost by: Davidb » Tue Nov 21, 2023 12:48 am

Multi layer
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PostPost by: Davidb » Tue Nov 21, 2023 2:48 am

I will be out of contact for 24 hours--please keep the suggestions coming though!
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PostPost by: rgh0 » Tue Nov 21, 2023 6:16 am

The MLS gaskets tend to be hard to get to properly seal on the twin cam head due the gasket stiffness and the Twincam head flexibility. I would only use composite fibre gaskets.

The oil leak problem is potentially due to the gasket not sealing.both at the fire ring and at the oil passage. This may be causing both combustion gasket leakage into the oil passage as well as oil leakage into the cylinder

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PostPost by: alan.barker » Tue Nov 21, 2023 11:06 am

Hi David,
Just to be clear N°1 is near the Rad.
N°4 is near Windscreen.
N°4 near the Windscreen can be a bit difty because of Breater Pipe and vapour from Crankcase.
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PostPost by: Davidb » Tue Nov 21, 2023 9:22 pm

Def. closest to the rad! (notaJag) However, since this is an early head it does not have the drain back drilling-next time the head is off it is getting drain back tube fitted!

Interesting comment about the multi layer gasket/flexible head. I had not considered that potential scenario...
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PostPost by: 2cams70 » Wed Nov 22, 2023 8:19 am

Is it oil fouling or soot? Is the engine blowing blue smoke? Usually oil burning smell and smoke colour is quite distinct from mixture problems.

I doubt it's the head gasket because to have oil enter the combustion chamber through the gasket would require the fire ring to be leaking. If the fire ring was leaking you would also have combustion gases leaking and if you had combustion gases leaking you would also have much more serious symptoms. Is the engine showing other symptoms?
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PostPost by: Davidb » Wed Nov 22, 2023 4:16 pm

It appears to be oil. With a BP6ES plug fitted it gets quite oily. With a BP5 less so.

I am sure I read a thread a while ago in which several people complained about this problem?
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PostPost by: nmauduit » Wed Nov 22, 2023 5:52 pm

2cams70 wrote:I doubt it's the head gasket because to have oil enter the combustion chamber through the gasket would require the fire ring to be leaking. If the fire ring was leaking you would also have combustion gases leaking and if you had combustion gases leaking you would also have much more serious symptoms.


I have no definite idea about the actual problem, but I'm not convinced by this argument: when the engine is running average pressure in the oil system is 60 psi, while at the seal ring it get higher only a fraction of the time. I've had a head gasket small leak that would go only one way (suck small amounts of coolant without increasing pressure in the cooling system, due to head corrosion) not a rare issue I'm sure others would have experienced it - though I understand that inadequate coolant is more prone to etch away the head material at a cooling port near the fire ring than at an oil port... in any case a lot of scrutiny would be to envision to solve the mystery (including valve stems and head itself )
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PostPost by: 2cams70 » Wed Nov 22, 2023 9:59 pm

Whenever I’ve had an issue in that area the oil leak is visible external to the block not internal. In any case you should do a compression test.
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