Oil leak advice required

[Rod1883]

Hi all,
Despite replacing the cam cover gaskets and half moon seals a while back, I'm still getting an oil leak at the back of the LH head and it seems to be getting worse.
After a run, oil sits on and runs down from the top of the transfer housing that is attached to the back of the head. It doesn't look, to me, like it is leaking from the half moon seal or the cam cover itself.
I'm wondering if it is coming from that transfer housing. Is there any oil routing in that transfer housing or is it purely for coolant flow?

Thanks
Rod

[barkerwilliams]

Clean the oil off and dust the area with talcum powder.oil leaves a good trail to follow

Start engine, remove oil filler cap from cam cover, how much air pressure is venting via the cap? Should be minimal. If engine is pressurised you will never stop leaks, stop one and the next weakest seal will leak.

[wilf]

Only water there AFAIK.

Probably worth checking that your cam cover is actually flat and straight - they can distort into a "banana" shape and then leave gaps on the seal to the head, especially toward the back of the head. I had to "re-educate" one of mine with a large hammer, and use loads of oil-resistant PU sealant anyway to finally get it oil tight..

Also check that your cankcase breather system (which should induce a slight vacuum inside the engine and thus help rrevent oil leaks) is working OK - at tickover, the engine should stall or run badly if you remove the oil filler cap. If it doesn't, then you most likely have airleaks and the tickover setting has been adjusted to cover that.

[DMT]

Check your oil dipstick is sealing. Should have a felt washer at the bottom.

[Rod1883]

Thanks for the advice. I will look at all those things suggested.
A couple of follow up questions:
What might be causing air pressure in the engine, if that is the issue?
There is a felt washer on the dipstick. I fitted one recently as there wasn't one there before. Could that in someway be part of the issue? What is the felt washer's purpose and if there wasn't one previously what should I look at that might need to be re-adjusted to reflect that there now is a felt washer?
Thanks again
Rod

[barkerwilliams]

All engines generate some crankcase pressure its the way they work, it gets worse with piston ring and valve guide wear. It increases gradually as the engine wears with age - the waistband effect!
All modern engines have a method of piping those pressurised fumes back into the inlet manifold or carb usually with the assistance of the vacuum generated by the inlet /carb and re-combusting them in the engine.

Modern engines aggressively draw fumes from the crankcase and the case often runs below atmospheric pressure and the engine needs to be sealed well on the dipstick and oil filler otherwise the engine will run badly as the additional air will weaken the mixture. Engines of the Stag vintage if in great condition tend to run with a slight vacuum at tickover and a slight pressure as the revs increase.

The dipstick tube is so low on the engine that oil tends to creep up the stick in use and can escape at the top, the felt stops rattling and once oily and wet sealed the tube, both for fumes escaping and air being drawn in at tickover. The dipstick is kinked so that it "locks" in place and holds the felt against the tube top.

If your car has been retro-fitted with an oil catch tank, or has the original carbs fitted with a length of rubber tubing then they may have blocked and a clean out would do no harm. The OS cam cover where the pressure vents to the carbs has a small internal cavity filled with wire mesh to assist in filtering the oil from the fumes this can also get blocked so it the cam cover is off run a little something (petrol, turps, carb cleaner, brake cleaner) through there to clean the gunk off the invisible mesh. Incidentally it is this mesh that retains sand if you get the covers sand blasted and then kindly returns the grinding material back to your oil and damages the engine.

If you remove the cam covers measure the width of the cam cover at the ends and compare with the centre measurement, the covers splay and he centre of the covers ends up too wide to seal well. Tighten them back is easy using a woodwork type clamp on the cover or possibly a vice or skilled(?) use of a soft faced hammer. Spend some considerable time getting the gaskets to sit well on the covers before replacing them or they overhang the milled face on the cylinder head.

Alan

[Lingen]

Rod.
There is oil routed behind the transfer housing, but it is an unusual place to get a leak.
Mike.

[Rod1883]

I've started on the process of elimination.
First up, cleaned the area around the back of the LH head - especially around the cam cover seal, the half moon and top of the transfer housing.
Applied talc and took the car for a run.
Upon stopping the engine and opening the bonnet, I was in time to see a bead of oil run from somewhere near the base of the half moon seal down onto the top of the transfer housing/head joint. It's a difficult area to see clearly so I'm not sure if the leak is from the half moon seal or the cam cover seal above - I'll do it again to check as if it isn't the half moon I'd prefer not to disturb it if I can avoid it.

I have a question though on what I've observed this morning. When I first opened the bonnet, I could see that the talc ion the transfer housing seal was all clean and dry after a 5 or 6 mile run so it seems that it was upon stopping the engine that the bead of oil I observed leaked down onto it. Has anyone any thoughts on why the leak should happen after the engine stopped, rather than whilst it is still running?

Thanks

[trunt]

I found that the half moon seals needed trimming on the flat edge to make them level with the casting, then they sealed ok.

Terry

[Lingen]

Rod.
Probably because the crank case breathing system creates a slight vacuum when the engine is running, which will resist small leaks occurring where there is a poor seal.. When the engine stops, they will dribble!
Mike.

[NeilR]

The current supply of 'Half Moons' do seem to be oversize.
Trimming them down as suggested above is the thing to do. I have done the same on the previous two engines I have had dealings with

[jbuckl]

Cam cover sealing works ok if the cover distortion has been attended to and:-
1 the cork gaskets are glued into place with contact adhesive with around 28 washing pegs all around.
2. Apply ‘dirko’ to the sealing faces of the d bung.
if they still leak it’s likley that the covers are still distorted.

[Rod1883]

Thanks again everyone.
Yes, the slight vacuum whilst running, then released when the engine is stopped, would appear to be the reason for the leak appearing at that point. At least that would suggest that the slight vacuum/crankcase breather is all working as it should.
When I did the cam cover gaskets and half moons a couple of years ago, and after thorough cleaning of all surfaces, I fitted the cork gaskets to the covers with Tiger seal (all clamped to a piece of wood overnight) and then used a smear of grease on the other face of the gasket before fitting to the head. For the half moons I used a smear of silicone sealant.
I'm pretty sure the covers were a good fit and flat/not distorted as I don't recall an issue when doing the work back then, but when I take the LH one off I'll check again.

Would the use of blue hylomar on the cork gasket/head mating face be better than grease and appropriate?
Re the Dirko product suggested above - is there a particular grade/type of Dirko to look for as a quick internet search throws up a few different types?

Thanks again
Rod

[Alacrity]

The half moon seals are rubbish & need the internal groove widening, then fitting with a quality sealant. When I rebuilt my engine I stood it on the flywheel end overnight & the oil that was used to assemble the cams started dripping out! Some folk said that was acceptable!!!!

[jbuckl]

https://www.ebay.co.uk/itm/232648374452?epid=249262149&hash=item362aec78b4:g:xJ4AAOSw43hauREs