Center main bearing

A

aermotor

Well-known member
Pulled the pan for a look around and found the center main Plastigaged out to .0025 with no shims left. What would you do? Polish the cap and try again, flat plan the cap on glass, machine shop down a tad or put it together and let it go if the others are better or no worse?

John
 
aermotor said:
Pulled the pan for a look around and found the center main Plastigaged out to .0025 with no shims left. What would you do? Polish the cap and try again, flat plan the cap on glass, machine shop down a tad or put it together and let it go if the others are better or no worse?

John
Click to expand...


Geez John, that's kind of a loaded question. If you are out of shims on that one, what are the other caps showing clearance-wise, and how many shims on those?


I would suspect the babbitt has been "beat" out of the center main, and if so your time is going to be limited. Caps that are filed are not the best for future rebuilds as the amount of babbitt that can be cast will be less on those.
 
If it’s this worn, you might do some checking on your rear thrust,to make sure it’s in spec, and it’s not cracked. If you plan on driving much, you really need to consider a rebuild, as I’m guessing you have a cylinder ridge and your valves are sunk and almost a sharp edge. In other words, they engine is tired and worn out.
Our Dr day team has done this bearing cap trick and it worked. A few hundred miles further and a piston broke. ( old piston, new rings.). Good luck
 
Depends on what you use it for..ice cream runs?either run it as is or dress the cap down to .002..most of the ones I've torn down are shimless,that's pretty common.
 
Do you have a micrometer ? If you decide to use a piece of glass and emery cloth on the cap then I'd recommend measuring in several spots first and as you sand. Its not much, .001" will do it. Have you checked the rear yet ?
 
aermotor said:
Pulled the pan for a look around and found the center main Plastigaged out to .0025 with no shims left. What would you do? Polish the cap and try again, flat plan the cap on glass, machine shop down a tad or put it together and let it go if the others are better or no worse?

John
Click to expand...

I flat plate sanded to approx. .00157 and will call it good. On to the rear main, the bearing is an insert not like shown in any suppliers parts books. It has machined thrust surfaces on each end, I haven't tried to remove them as I don't want to bust them. Removed 1 shim on each side and came out an even .0015 front to back. I guess I have a 1928 hybred. If the front comes out good I'm hitting the road. Other signs of a worn out engine like Brent and Chuck Sea / Tac mentioned appeared OK, valves were standing tall and no discernable ridges in the cylinders - just he main bearing (so far) down to no shims.

John
 
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