Rear main oil leak -help please!

[SimonBrown]

Having recently had the engine out of my Series 2 OTS to fit a new clutch, rebuild gearbox and fix a rear main bearing oil leak (split lip seal) I am delighted the car is completely transformed to drive. After about 100 miles of varied spirited driving the car was completely free of oil leaks!
I drove to Gaydon this morning, on an A road, at varying speeds, checked the reaction plate (where the oil previously dripped from) and it was dry.
However, after a motorway drive home, 30 miles at a pretty constant 2500 revs, there is again a considerable oil leak🥲
I am sure it is the rear main as there is evidence of oil on the flywheel.
Initial thoughts are crankcase pressure building on a light throttle at relatively high engine speed. But how?
The breather is clear, and the gauze flame trap. The car is running triple SU’s.
Is it possible the crankcase is being pressurised from the inlet manifold?
Any help/ideas would be much appreciated
Many thanks
Simon

[mgcjag]

Hi Simon.. is your breather plumbed into the air intake..also quite ofter the rear sump seal is the culprit..Steve

[bitsobrits]

To answer your question about the inlet manifold pressurizing the crankcase: No. How would that even happen? the inlet manifold and the airbox are seeing negative pressure when the engine is running.

You first need to positively identify the source of the leak before you and all of us on this forum jump to conclusions and suggest remedies. Are you positive it's not the upper banjo bolts feeding the cams? Oil leaks from these bolts are common and can be hard to detect visually. Do the clean dry rag or hand test all around the rear of the head and block and the cam feed oil line.

Have you overfilled the sump? Even a quart over can markedly increase the likelihood of a leak. I would never rely on a dipstick, unless it's been calibrated to the engine in which it's fitted. Better to count the quarts/litres going in after a total drain (including filter replacement) and verify the dipstick markings. I run my car with 7-8 quarts in the sump and have marked my dipstick to facilitate maintaining the level in this range. I'm not running my car at constant high rpms so have no concerns. This greatly reduces the tendency for rear main leaks.

[SimonBrown]

Hi Steve,
Hope alls well with you and thanks for your response.
Yes, breather plumbed in to carb side of air filter as standard.
What I really don’t understand is that it has been completely dry over 100 miles brisk driving and been completely dry.
As soon as I subject the car to cruising at constant speed, 60-70 ish it leaks quite badly?
I am pretty sure it is not sump seal as this has been very carefully assembled because of previous issues.
Simon

[SimonBrown]

Just to add,
It is not the cam feed pipes, they are dry.
The oil level is half way between min and max.
I have checked the dipstick and it is correct length and marked E

The recent engine strip revealed a leaking rear main bearing seal, hence a very careful replacement.
Seal split at 8.10 so the split is out of line with the housing.
Rtv used on all potential leak passages

Due to evidence of oil on the flywheel looking through the front bell housing hole, it appears to be running from the centre of the flywheel radially.

It is completely dry unless subjected to constant highish speeds.

It then leaks, and quite badly, when driven at constant speed at over 2500 rpm.

Which leads me to excess crankcase pressure, but the breathers are all clear.

Simon

[bitsobrits]

But how many quarts are in the sump? Seems you missed my point about dipstick readings.

[mgcjag]

Hi Simon...yes as Steve mentions above...correct dipstick aside it's essential to measure the correct amount of oil into a dry engine then mark its level on your dipstick...A split rear seal dosnt inspire me with confidence...iv read about too many of them leaking..especially critical is how well the seal is cut..often a ragged not perfectly square joint..Steve

[SimonBrown]

Sorry, didn’t miss your point. 8 litres of 20/50 oil were put in the sump, which is approx 14 uk pints and 7 uk quarts.
Not sure if UK quarts are the same as US.
This equates to the dipstick being half way between min and max, after the engine has run to fill filter.
Jaguar state 8.5 litres to max including filter which all sounds about right.
Thanks
Simon

[SimonBrown]

Hi Steve,
The oil seal conversion was originally supplied by Terrys Jag Parts in the US, but fitted incorrectly according to Terrys YouTube installation video. I.e seal split was horizontal and no rtv used.
It is not necessary to cut this one down, it squashes in to the recess on fitting.
I share your reservations with a split seal, but I had no alternative as the crank had been ground to fit, and at a smaller diameter than the more common uk supplied kit.
However Ifollowed the video very carefully and believe this can only be leaking now due to excess pressure at sustained motorway speeds. I suppose there was an alternative of a new crankshaft🥲

Thank you
Simon

[SimonBrown]

Apologies Steve, please ignore my last post, it was not the Terrys Jag installation that was installed.
This one didn’t need to be cut to suit, and should have been installed with the split out of line with the horizontal housing
Simon