Classic/Antique Car Repair: Austin Healey oil leak, oil filler cap, crankcase pressure

Question
I have about 1,000 miles on my rebuilt 1960 Austin Healey 3000. I did the engine rebuild myself and I'm aware the the rear bearing has no oil seal and will leak. Today at the end of a 20 mile brisk drive I noticed smoke coming from under the car. It was from oil getting on the hot exhaust and burning off. The oil drips from the joint where the transmission bolts up to the engine, blows over to the exhaust and burns off. There is an after market fix for this rear bearing leak, a metal diaper that bolts on the back engine plate. Do you think this repair could be done by dropping the transmission only to access the back engine plate? Also, do you think that this volume of oil out the back is unusual? There is no over heating, no loss of power or oil pressure and no funny noises. Just a little smoke. The drip stops within a minute after parking.              Scott  

Answer
Hi Scott,
An excess leak at the rear main (if that is what it is) can come from several reasons. You should not have a leak to the point of oil getting all over the exhaust. The Healeys did drip a little oil but only a couple of spots on clean concrete after driving.
How much bearing clearance did you have on the mains? Another cause is crankcase pressure. This will cause the rear main to leak even when the bearing clearance is correct. You said you have "a little smoke". Do you mean blue smoke out of the exhaust? Were the cylinders rebored and new pistons installed or just re-ringed? and if re-ringed did you deglaze the cylinder walls? And did you install chrome rings?
Here is a rough test you can do. Run the car until the oil is warm. (longer than coolant temp up to par) Clean the valve cover and than remove the oil filler cap and tape an old towel over a large area of the valve cover around the area of the open cap. This is to give a large area for the crankcase to breath into the towel. The towel will keep all the oil steam confined but relieve any crankcase pressure. If it don't show a lot of leakage at the rear main than it is crankcase pressure that is causing the problem.
If you installed chrome rings on cylinder walls that were not deglazed or worn too much you will have a very long brake-in period for the rings. If your rings were chrome "New old stock" they may be the old "Hard Chrome" and very hard to get seated. Newer chrome rings have a face of what was called "Soft Chrome" face that would seat well on old cylinder walls.
Do a "Wet" and a "Dry" compression test and let me know the results. You can contact me at longez8@bellsouth.net
Howard