Lotus Elan

Cam Caps replaced?

PostPost by: JJDraper » Fri Feb 28, 2020 7:34 am

A thought just struck me as I was reviewing pictures of my recent engine rebuild. The engine has always suffered oil leaks from the 'D' plugs, which seem to stand proud off the head by a mil or so. I have always accepted this and put it down to being a Lotus. All the cam caps have their number stamped on them, with the matching one stamped on the cylinder head. In addition, their is a 'V2' stamp on them all, including the head - see picture. I wonder if the head has had new caps & been line bored at some point in its life? Has anyone else seen this before? It would explain the problem with the 'D'plugs..

Jeremy
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PostPost by: nmauduit » Fri Feb 28, 2020 10:23 am

I would think that a camshaft linebore would tend to decrease the amount by which the half moon stand proud, no increase... and a good machinist would probably line up to the lowest bearing level in the head and take some material from the foot of the caps so that the new axis after line bore is almost the same with respect to the head.

A top head skim (to take up severe warpage?) would go in the direction you describe - but I rather suspect that half moons not flexible enough (too old?) or not properly seating (center nipple at the bottom) would more likely be the cause of the observed leaking side effect.
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PostPost by: sprintsoft » Fri Feb 28, 2020 12:00 pm

Hi Jeremy,

I’ve had several Lotus over the years and found most of the new rubber D half moons sit slightly proud, 1mm sounds ok as these will normally squish down as you tighten the cam cover.

Do you use any type of sealant?

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Iain
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PostPost by: JJDraper » Fri Feb 28, 2020 4:37 pm

nmauduit wrote:I would think that a camshaft linebore would tend to decrease the amount by which the half moon stand proud,


On reflection, you are right.. I have used 'D' plugs from a variety of sources and they are all pretty hard, apart from one batch that swelled up ridiculously - see pic. Always used the same oil, so that was not the cause. I can't see them being squished down by the cork gasket, which is where they leak. I do use minimal sealant.

Still no answer to the 'V2' markings..

Jeremy
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PostPost by: rgh0 » Sat Feb 29, 2020 12:46 am

The V2 markings have been added perhaps by an engine builder to keep track of multiples sets of cam bearing caps and heads. The number stampings for the cam caps and on the head look original so it does not appear that the top of the head has been machined.

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PostPost by: 512BB » Sat Feb 29, 2020 9:49 am

It is possible Jeremy, that your head was built by the infamous Twin Cam engine builder Von Braun, and he expected the motor to go like a rocket :lol:

Having used D plugs from many different suppliers over the years, some stick up above the top of the head, and some sit flush. The ones that stick up, I trim with a stanley blade before bedding down with some RTV. Let the RTV set, then I run a bead of RTV on the inside of the D plug. No leaks. Never re use D plugs, false economy.

It looks like your head has either gone a bit soft, or has been over tightened in the past, judgeing by the washer recession.

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PostPost by: JJDraper » Sat Feb 29, 2020 10:37 am

512BB wrote:It looks like your head has either gone a bit soft, or has been over tightened in the past, judgeing by the washer recession.


Yes, before my ownership. They were 'spot faced' by QED when it had a full refurb by them in 2003. I had no idea what 'spot facing' was, when I saw it on the invoice... Doesn't seem to have got any worse in the intervening time & mileage (100k). Perhaps using a torque wrench helps.

The motor does go like a rocket when the stars (and cam timing) align.

+1 on new D plugs, and I keep a few in stock.. along with exhaust gaskets, filters and other miscellaneous parts that could spoil a weekend if I was short of them.

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PostPost by: Mudmouse » Sat Feb 29, 2020 11:45 am

Jeremy,

I have just fitted new D/Half Moon Plugs to my engine after trying to rectify an oil leak from the plug area. On fitting them dry I found that they stood proud about 0.8mm which I thought was too much for the gasket to accommodate as a step or to compress. I ground mine down against the side of a bench grinding wheel being very careful not to grind them at an angle or too much (or removing too much flesh). By carefully doing it I ground the top flat side down so that I took them down to about 0.2mm proud when fitted.

On reassembly and careful torqueing of the cover nuts over a few days both cold and hot I seem to have got rid of the oil leak.

I used Wellseal to first fit the cork gasket to the cover then a smear of silicone grease on the head surface (for easier removal at a later date) and Wellseal on the curved face of the D plugs. First time I have used Wellseal - it did not fully harden (which I believe it is how it works) and is still sticky at the joint after a week.

Time will tell if the leak returns!!

Steve
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