Rear main bearing modification

[RossV]

About 40 years ago when building the engine for my 27 Chummy I carried out a modification to drain oil from the rear main bearing but cannot recall the details of this modification. I’m now building an engine for another car and would like to know if this modification is still considered to be worthwhile. If so can anyone provide the details please.

[Steve Hainsworth]

Hi Ross
You only need to do this mod if you are changing to a 1-5/16 crank or larger. This is because of the larger OD roller bearing having a steel dished washer behind it to throw the oil outwards instead of a felt seal held in with a circular steel plate behind the flywheel. The hole is drilled using the bigger steel bearing mount as a template and this allows the flung oil to escape back to the sump. When the big crank was introduced a new bearing housing (with a hole at the bottom rear coinciding with a hole in c/case leading down to the sump area) was introduced at the same time along with an oil slinger and aluminium cover plate between bearing and flywheel
The flywheel has an aluminium plate behind it in this set up and has a scroll machined into it where it meets the flywheel boss to deal with any oil getting past the oil slinger.
So don't worry if you are keeping the small crank, as the felt seal will work fine if all the parts are in good condition

[AustinWood]

We made this modification on our 1-1/8" crank engine while incorporating a lip seal.
It seems to me that any oil getting past the bearing will just stay there and get more and more contaminated. Also if oil can't get out then it will restrict oil getting in.

[RossV]

Thanks Steve. I should have phoned you before searching the world! I am using a 1-5/8 crank and hope to be able to fit modern oil seal in the aluminium plate.