Excess Oil Pressure??

[mof]

1098cc circa 1970 with about 120,000(ish) on the clock.

Just had to replace the head due to a burnt out valve. Before I took the old head off I spotted an oil leak at the front nearside corner of the head gasket. There seemed to be an oil channel close to that corner of the block.

I put the new head on. All 4 pressures are fine.

After about 40 miles the oil leak has come back.

I have yet to retork the bolts.

Is it possible that this engine has a blockage which bumps up the oil pressure and gets past both the old and the new gasket.

I have noted that, since fitting the new gasket, the idle speed drops really low when I take the oil filler cap off.

Previously the revs used to drop hardly at all, but now there is a noticable drop off in revs, so much so that the car almost stalls if you try it from cold.

This car has the re-breather system which pipes crank gasses back into the carb inlet.

Is there some connection between this and a possible excess oil pressure?

Blocked filter in sump is about the only thing I can think of, but would that have this effect?

Thanks

Steve

[Willie]

Your oil filler cap should be the type with a built in wire mesh filter and when
you remove it the revs should drop (proves that you have no leaks in the
system). Presumably it weakens the mixture if done when the engine is cold
so that it tends to stall but I am not sure. If you have used a copper head
gasket then yes, it does need retightening after a short time but the oilway
is very close to the edge of the cylinder head so it is vital that the head and
block are in good contact in that area.
EDIT....does your breather outlet pipe go straight to the carb inlet or does it
go to a valve arrangement mounted on the inlet manifold and then to the carb. You can check for a blockage in the supply to the rocker assembly with
a quick look...there should be oil oozing from the rockers and all over the
valves.

[mof]

Thanks Willie

The cap does indeed have a wire mesh plug in it.

It sounds like the revs dropping feature is an indication that things have improved since the head was replaced, rather than a bad sign!

The breather pipe returns to the inlet side of the carb, just prior to entering the inlet manifold. I've never checked to see if there is a valve of any sort in there, I shall have a look.

Hopefully the re-torque will stop the oil leak, but I am pessimistic!

Thanks for the help.

Beautiful car by the way.

[Willie]

MOF.... the valve to which I referred cannot be missed! it is a large mushroom shaped metal thing with a spring clip holding the top on mounted
on the inlet manifold. it contains a diaphragm which causes all sorts of trouble if it splits. It was not fitted for long. Regarding your oil seepage, since
you have fitted a different head,presumably refaced so that it is flat,then your
block surface may be the culprit, fingers crossed for the retightening.

[chickenjohn]

My 1969 Traveller has the mushroom shaped breather valve- amazingly though, the replacement diaphragms are still available!

[mof]

No, nothing like what you describe.

Fingers crossed also.

Steve

[bmcecosse]

Just make SURE oil is still reaching the rocker gear ok - look inside with the filler cap off and engine running - there should be plenty of oil to see. If none - stop engine immediately!! Are you sure the gasket has been put on right way round ? Excessive oil pressure is highly unlikely - and certainly would not be caused by a blocked oil intake filter - quite the opposite! If you have a gauge it should read ~ 60/70 psi when running at 60 mph with hot engine. But even 90 psi (which my Mini has) should not cause a leak at the rocker feed.

[mof]

Thanks for the advice bmc. As the oil loss was occurring before I fitted the new gasket, so I am not in a blind panic just yet!

I think I shall have to take it off and clean up and try again.

Someone suggested using a run of Hermatite (I think that's the spelling) round the oil feed in the gasket.

I am confident that there is oil getting to the rockers, as they seem wet enough, although you cannot see it spraying too much.

I supose loss in oil pressure must be occurring to some extent.

How do I measure the psi on the oil system?

Thanks

Steve

[Alec]

Hello Steve,

a blocked\stuck pressure relief valve will cause excessively high oil pressure, especially on a cold engine but is rare.
You will need to screw a gauge into an oil gallery tapping to measure it, and the easiest is where the oil pressure switch is connected. If you don't have a gauge I would not worry too much. Re-torque the head and check how the leak is then.

Alec

[rayofleamington]

If/when you take it apart it would be worth to check how well the gasket lines up with the oil feed holes.
Maybe you have a block on the edge of tolerances so the sealing ring in the gasket doesn't sit properly?
It's a bit of a longshot, and seems more likely to be a flatness problem

[bmcecosse]

I doubt Hermatite will do anything useful! If you have the head off - probe the oil gallery connection in the head, and make sure the rocker gear has the correct pillar above the oil hole - it's the one with a hole in it! But if the rockers are 'wet' that should be fine.

[Cam]

I would not personally recommend putting instant gasket on a head gasket. I have seen it done before but it can cause unevenness which is best avoided. If you are using a quality head gasket and still getting leaks then check the block & head faces for trueness.