Main Bearings

johnr9q@yahoo.com

johnr9q@yahoo.com

Senior Member
This is what my main bearing fastener looks like. I was expecting a castle nut with cotter pin. This looks like a pipe plug. Also, on my rod bearings, I plastigauged all of them and adjusted the shims but when I put one of the caps back on, I can hardly turn the engine over. I take that cap back off and the engine turns over like it should. I think I removed all the Plastigauge material. How do you remove the Plastigauge Material?
 

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that is a square headed bolt that is used on the main bearings. the nut is on the other end of it.
the plastigage should come off easy with your fingernail. then wipe it clean.
 
one handy pc of info for you for when you put those bolts back in.
on the square head of the main bolt there should be a bump, that bump is the location of the cotter pin hole on the other end. so you can make the cotter pin hole the rite way around making it easier to install them.
 
On the rod cap in question, make sure that you have it installed in the proper direction. Also make sure that you don’t have a piece of shim intruding into the bearing surface. Does that piston go up and down in the cylinder smoothly? You might also mic the journal carefully to make sure you don’t have some ovality or taper wear on the journal, which would give you a false Plastigage reading. And, is the bearing surface surgically clean?

Acetone or carb cleaner might help soften the Plastigage.

How much shim did you remove from that rod compared to the other three? Did you remove equally from both sides?
 
old ugly said:
one handy pc of info for you for when you put those bolts back in.
on the square head of the main bolt there should be a bump, that bump is the location of the cotter pin hole on the other end. so you can make the cotter pin hole the rite way around making it easier to install them.
Click to expand...
I’ll be damned, I didn’t realize that. Learn something new here every day! Thanks.
 
If there is no problem with the way the bearing was installed then you may want to put back a 0.001 shim on one side of the bearing. This will increase the clearance by 0.0005.
 
Can I just loosen those square headed bolts on the main bearings and plastigauge the mains like I did the rod bearings?. Old Ugly says there is a cotter pin, I don't see a cotter pin.
 
Jay Jay, you asked: On the rod cap in question, make sure that you have it installed in the proper direction. (yes I did). Also make sure that you don’t have a piece of shim intruding into the bearing surface (I tried very carefully to insure that didn't happen, maybe I need to get some new shims, the old ones looked black and ugly. I tried to clean them up but couldn't) . Does that piston go up and down in the cylinder smoothly? (Yes it does) You might also mic the journal carefully to make sure you don’t have some ovality or taper wear on the journal, which would give you a false Plastigage reading. (I will do that and get some new shims) And, is the bearing surface surgically clean? (I tried to get it as clean as I could) How much shim did you remove from that rod compared to the other three? (I removed one shim like I did on the other three) Did you remove equally from both sides? (I believe so. When I get the new shims, I'll insure I use an equal amount on each side) Thanks again so much Jay Jay (and others)
 
Plastigage operates by the "crush" you impart in putting the bearing back together at full bolt tension. You measure the clearance by the green gauge on the wrapper showing different "widths" of flattening out.

I have carefully peeled the plastigage (on rods particularly you leave a pig tail hanging out to grab it) and then used a standard micrometer. Supposedly in the "real old days" before plastigage the mechanics would use annealed lead wire for the same purpose.


Joe K
 
Having one less 0.001 shim on one side of the cap will not matter. They don't need to be exactly equal but should be within the 0.001. That way you can add or subtract 0.0005 from the clearance.
 
The square heads are on the bottom (pan side) of the bolts. The bolts go upwards and are topped with a castellated nut and cotter pin. You will find the nuts for the front main bearing just behind the timing gear housing, front of the engine, visible from the left side. The nuts for the center main are between cylinders 2 and 3, one visible exterior on the left side of the engine (behind the water inlet), one is within the valve galley.
 
johnr9q@yahoo.com said:
I do not understand how to remove the main bearing caps.
Click to expand...


Remove the cotter pin
HOLD the upper exposed nut using a socket or even a combination wrench.
TURN the square exposed at the crank bearing and undo the bolt.
Withdraw bolt from each side. Cap should drop into your hand.
Gather up any shims you find and mark carefully (sketch) from where they came.
VERIFY the orientation of the cap is correct as removed.

The entire task is a LOT easier with the engine removed and turned upside down. Gravity is a force and having the entire crank/flywheel assembly over your head waiting to rearrange your nose is not fun.

I have one of the versions of these...

Cheaper than a plastic surgeon.

SF750LBS4870PV0%2Fgoods_thumb-v3%2Fengine-stand-f1.jpg


Joe K
 
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To remove the engine I have an overhead gantry crane I made from 4x4 uprights, 2x10 horizontals/legs against overturning. I did the engineering and it's good for up to a ton.


I use a Harbor Freight 1 ton hoist. suspended from a movable hook. I lift the engine using the 3rd spark plug hole. A plug has had the internals removed and a lifting eye put through it. It will work either with or without the transmission attached. A little better balanced without the ******.


Joe K
 
FWIW, those square heads on the main bearing bolts are the same size as plumbing fittings. Henry made them that way expecting that just about everybody with plumbing in their homes, already has a tool for it. That is not so these days.
I file the square down to 1/2" and use modified 1/2" drive socket fittings to hold it.
 
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