QuestionI have rebuilt the engine in my 70 MG midget(or rather my mechanic has)He could not find a rear plate or gasket.the existing rear plate had a hairline crack.When I got the car back it was leaking about a quart of oil a day.So we replaced ther rear plate and seal.Once again it is leaking about a quart a day.It only leaks when the engine is under pressure as when driving on the freeway.Is this a common problem? any help you could give me would be appreciated.
Thank you Lorri Curtis
AnswerHi Lorri,
No, it is not common for a Midget to leak a quart a day. I assume the leak is still at the rear of the engine.
You need to wash the engine down and raise the car on a lift while it is running and try to see where the leak is originating from. If it is leaking out of between the bell housing and the rear engine plate it can be either the rear main or the oil pump or cover. This requires that the engine be removed to examine and repair.
However, if the mechanic has done this already and was careful about the work in that area, you need to look at the crankcase breather on the side of the block and from the valve cover. If either are partially blocked crankcase pressure will build (like on an expressway) and force oil out the rear main which does not have a seal.
Another possible is since this is a new rebuild, what was done in the piston and ring area? Was this bored and new pistons installed or was it just re-ringed? If it was re-ringed, were the cylinder walls properly deglazed and were chrome rings used? If chrome rings were used and the cylinders were deglazed it still takes a long time for the rings to seat (seal) on the cylinder walls and if the walls were not deglazed properly the rings will never seat. If it was bored and new pistons installed it may still take as much as 1500 miles to seat the rings.
When an engine is under load like driving fast, there is some piston "blow by" which goes into the crankcase. The breather pipes are designed to releave this pressure. If that pressure can not excape then the pressure tries to get out at all of the openings and since there is no rear main seal (only a spiral drain)It blows the main bearing oil out of the engine into the bellhousing.
The side cover vent on some of the Midgets had a wire mesh inside that is difficult to clean and if it was just washed it could be partially clogged.
Another possible is that the pressure regulator valve on the side of the block is not correct meaning some one previousely may have jacked up the spring pressure to gain more oil pressure and when the engine was rebuilt with either just new bearings or the crank was turned and new gearings installed thus raising the oil pressure and with the spring still jacked up the oil preeure goes too high which forces too much oil through the main bearings and at high RPM floods the rear main drain back system. You should be able to spot this fault by reading your oil pressure gauge while on the expressway. It should not run over 65 PSI.
One last thing, If your expressways are like they are here, the traffic runs 75 + MPH and the Midget was not designed to cruise at those speeds. And only a very good engine can operate at that speed without problems.
I hope this info helps, let me know.
Howard
