Due to the fact that the rear main seal leaks and that oil pressure is only 10 at high speed and 2 or 3 at idle, I suspect that my machinist did not get main bearing clearance tight enough. This may be due to the fact that the stupid shim kit I got from egge for $50 only came with one pair fat shims per cap. What is the best way to measure clearance while not pulling anything major?

Remove oil pan. Remove one main bearing cap at a time. Support the weight of the crankshaft near the bearing having the clearance measured. Use plastigage to measure clearance. Should be from .001" to .002" so get plastigage that measures from .001 to .003" (green print on paper packing). The bearing shims should be laminated so a shim or two can be peeled off as necessary....check shim for this.
If the mains are that loose you will hear a distant knocking when first starting in the morning and the knock will disappear in about one or two seconds. Will also pound a bit under load .
I think the instructions for using plastigae are on the package - if not I can furnish them.

Sounds easy enough.
No, the shims are single fat pieces of brass. I will be making my own shims because I can't find the proper .002 and .004 shims. Should have been more careful with the originals.

What is the proper oil pressure? Also do you think I can just replace bottom of main seal?

The 1940-53 low pressure engines will give 14 to 15 pounds of pressure at 50 MPH with a "medium" oil like 10W-30 after driving for 1/2 hour. At idle should be about mid-way between 0 and 15 pounds. Like 7 pounds.

Take another look at those shims. Use a magnifying glass, if necessary. Like Gene, I think the shims are there. They are sorts of clad. If so, you will be able to detect slight ridges along the sides and ends of the "block" of them. They are really thin. Get them started and you can peel off whatever amount needed to give the proper clearance. Nonetheless, I could be wrong.
Best,
Charlie

BTW: It sounds to me like you need a least a minor overhaul. Did you do a compression check? And, if you think the mains have too much clearance you may need take some shims out not put some in.

I hope not. Just got it fully rebuilt.

Oops! I forgot that you had disclosed at the outset that you just had it rebuilt. Charlie

There are shims being made as replacements by Federal Mogul and I believe that they are something like .006" thick. I bought a set and realized how useless they were. They were not a stack of shims. It was quite a shock seeing something like that with their name on it. I made shims from .002" brass stock from Car Quest.

Are you guys absolutely sure that your not mistaking those .006” shims for a solid single shim? A single .006” shim is pretty much useless when making this kind of adjustment and even a .002” shim is sometimes to coarse of an adjustment and a .001” or .0005” might be needed. I find it hard to believe that EGGE and Federal Mogul are selling a solid 006” bearing adjustment shim. As Charlie mentioned, laminated shims are pressed together under high pressure and sometimes it’s really hard to see the laminations or pick up an edge.
If you do have to make your own, McMaster sells laminated sheet shim stock in brass, SS, and carbon steel in stacks starting at .006” on up, with .002” thick individual laminations. http://www.mcmaster.com/#shim-stock/=66nolt . They also carry individual sheet stock in brass and SS down to .001” and you can get it in rolls of SS down to .0005”.
Denny Graham
Sandwich, IL

"we guys" are not sure of anything. King will have to remove a shim and examine it for him to be sure. We can only hope

I got to this over the weekend. The shims were all .006 solid brass. I was unable to peel them so I inspected them under the microscope and they were quite clearly solid. A call to Egge confirmed it. So I bought .006 laminated brass with .002 laminations and made my own shims.

I had used permatex #2 to seal the oil pan gaskets and thus the oil pan was a gigantic pain to remove. When I reinstalled it I used no sealer. Don't want to go through that again.

I used the green plasti-gauge and the clearance was over the limit of that type of plasti-gauge. I ended up only using .002 of shim under each cap and got a clearance of .0015-.002 on all bearings. I also changed the bottom half of the seal but the engine still seems to be suffering from a slight drip and being parked for a while.

After I was finished I took it out to drive for an hour or two and was disappointed to notice only a small improvement in oil pressure. Since I couldn't figure how reducing clearance by .004 would have so little effect, I bought a oil pressure gauge that read from 0-15 psi and installed directly on the outlet for the gauge. Then I proceeded to haul concrete to a recycling facility for a couple hours to make sure oil was fully heated. Then I checked the oil pressure and found it to be 6.5-7 psi at 600 rpm and 15 psi at 1600 rpm. So is everything OK? Could there have been excessive clearance and a less than accurate oil pressure gauge?

From your "story" everything sounds normal and OK.
Thats why I use grease to hold gaskets in place.
It is a must to stick up the side corks first and then the end corks. If not done in this order there will be a leak where they join and look like a main bearing leak.

I have a question about checking the main bearing clearance with the motor in the car. It hasn't been mentioned but what about placing a small piece of .001 or .002" shim stock on the main cap bearing surface and checking for binding after bolting up the cap. I thought this was an accepted method also.

The mains can be adjusted "in the car" by;
Removing shims untill a drag is felt when rotating the shaft and then adding a shim. Difficult to do with rods connected.

Using plastigage but weight of shaft must be supported by a jack or?

Laying a piece of shim stock on the insert -lower cap- as you mentioned. This was never an approved Chevrolet way but it works.

The mains can have a bit more clearence but the rods are best adjusted using the Chevrolet shop manual process.

Thanks for the help. I did install the oil pan gasket in that manner but the rear main seal seems to still be leaking. I will worry about it later, thought.