[Kohnke Rebabbitting]

The drilling of an oil hole in a rear main cap, in the middle, and then cutting a groove in the Babbitt, from the hole to the front end of the cap, and down the thrust came out in the 30's, in a magazine, under ( Tips from Mechanics ). All it is, is a butcher job on the cap. While it does get rid of oil, it gets rid of much needed oil to the rear main. You cheat the bearing, and it will wear fast. It is like many Builders that don't put any oil grooves in, Model A's can't run with out them.


Instead of getting rid of so called excess oil, which there isn't such a thing. Using a butchered rear main cap, is like carrying around a 500 gallon air tank, because there is a nail in your tire, and not fixing the cause of the leak. Also, putting a bigger pipe on is like putting in an over size door, with the hall way that is leading to it being still smaller then the door, you gained nothing.


There are only just a few causes to a rear main leak.


1. Plugged Breather pipe.


2. Main on the crank wore uneven.


3.Crank mains reground, or wore off center.


4. Motor bearings, wore, or Aligned Bored, or wore off center. If you set a crank that is not in a true alignment through Wear, in crank grinding, and, or, align boring. When the Motor is running, the flywheel effect will force the crank to straighten in Alignment, as much as it can, so if you set the crank in one Position, and when the Flywheel is running it in a different Position, wear is eminent.


5. All main caps have to have there part lines flat, and a perfect fit, to each other. If they are not, and they rock on the block even a little, when they are tightened, they will twist, and in case of Tinned caps, it puts a tension on the bond, and can, and will brake out the Babbitt from its adhesion, that is if the builder knew how the bond in the first place. Same thing, only worse, on Peened, or even worse on Babbitt that isn't Peened.


6. As Marshall said, you have to have sealant on the shims, and also top and bottom of the rear main bolts. I also put Sealant on the 3 front and center nuts to the outside of the block with new lock washers on all 4 front, and center main nuts, along with New lock washers.


7. You have to check to see if there is Babbitt in the oil passage in the rear main cap. We always pull the plug, and run a 3/8's drill bit through the cap. If you have a old style cap, bore it out to 3/8's, never use them that way. ( Use every drill bit, from 5/16, to 3/8's, or you will have trouble ) If you use a new pipe, screw in the pipe snug, and mark what sticks up in the inside, and saw, or grind it off, leave about .020 thousandths sticking up. Use a saw file in the middle of the pipe, when it is in and welded. We wire weld on both sides of the pipe so it won't come off in use. Then go and run the drill bit through again, cleaning the passage up. Don't put the plug in until the Babbitt work is all done.


8. We set end play from .003 to never over .004 thousandths. .006 is wore out. Yes, they will still run, but don't complain about the oil ! When you cut the thrust, you have to have it all the same length, and a 100% fit to the crank thrust face, or the high spots wear off, and the crank has to much end play.


9. The shaft clearance should be from 1.000-60, to not over 2.000-10. That is .001 thousandths Per Inch!


10. You have to have the flange Face trued, so there is no wobble in the flywheel, or it can also tear a remain up, and really cut power.


11. On of the most important things, is getting the flywheel housing set at a perfect right angle to the crank, if not, that will tear them up also, and give you a Ream Main leaker !


12. Connecting rods, will also give you Premature wear, that are not balanced, an OUT of Alignment !


There, I have again told you more then I know !


Thanks,


Herm.