Main bearing problem

[cowboy]

Hi Western Cub

I agree the first step it to check for the correct bearings.

Second check to see if the caps are in the right location.

How were the old breing coming out of the engine Was their copper showing in or worn thinner in one spot indicating out of round line bore

If the bore is out of alighnment it can be line honed to bring it back to alighnment.

Good luck

Billy

[George Willer]

A bit of an insight on line boring.

I bought a baler engine to use for the tricycle Cub when I was building it. On teardown it looked great from the top end... no cylinder wear at all. The bottom end was quite another matter. From all the nasty scars on everything it had obviously thrown a rod at high RPM in the past and was repaired. It may have been all right except for one thing, a main bearing cap was broken in two. I scrapped the engine and used another.

I did learn the procedure used to put it back in service if I chose. All 3 main caps would have a little milled off the mating surfaces (I had a good cap available from another engine). Naturally the holes would be out of round so there would be enough "meat" to bore them back to standard and perfectly in line.

[Western Cub]

The crank was ground to -.10. I got the bearings at napa. The bearings were removed by the machine shop. I had to buy the new ones on my own. Ill try the advice but have a question. Does the bearing with the lips on the sides fit in the center main bearing. It looks like that how it goes but Im checking.

[Boss Hog]

Yes
David

[Rick Prentice]

One thing I didn't see anyone suggest, and that's to wipe some oil or lubriplate grease onto the bearings before you set the crank in place, so you're not spinning it dry as you're checking things out.

Rick

[Eugene]

Plastiguage is done dry. Then the bearings oiled.

Check the numbers on the back of the (a) insert. One set of numbers should read .010.

If the numbers are not .010 - take them back to NAPA. Actually I'd take them back and have them show me that they were the bearing I ordered.

Eugene

[BigBill]

If the caps aren't closing up you may have the wrong sized bearings.


Assemble the crank into the block without the rear main seal in it. Then put a little piece of plastic gage on each journal. Then torque the bearing caps to the proper setting without turning the crank. Then remove the caps and check the plastic gage for clearance. Then clean off the plastic gage and put in the rear main seal, oil the mains, oil the crank and the seal lips and assemble and torque the main caps. The crank should turn with a little drag from the rear main seal.

Did the main bearings come in one box?

I worked at a dealership as a mechanic and the head mechanic gave me some main bearings in all small boxes there wasn't one large box holding them all. When i asked him for some plastic gage he told me we don't use that here. Welcome to shoemaker 101 right? Well after assembling the engine and putting it in the car it wouldn't turn over it was too tight. It turned out that one of the bearings was for an undersized crank. Well it was 5pm and time to go to my second job he had to finish it up. Never, never try to change the process no matter what and you'll never go wrong nor have to do it twice.

BTW; I put extra permatex on the pan gasket to break his stones, I knew the crank was tight but i put it in the car anyway. He had to take it apart and fix it.