400 mains undersized
 

In need of undersized .001 main bearings.Who sells them street strip usage .Target clearance .002 ,now at .0035 -.004.Another question what is the total undersize is it .002 when using the .001 bearing as a pair or is .001

Well, you have a bit of an issue there if your goal is .002" main clearance. I believe what you really need is bearings that are + .001 to tighten your clearance. I don't think anyone makes + .001 or -.001 for that matter for Pontiac mains. Not sure what bearings you are checking but basically you have race bearings available from King and Federal Mogul. Street bearings available from Clevite, Federal Mogul, and King, and ACL, but they are hard to find. Generally speaking, the street bearings will provide tighter oil clearance than the race bearings. Not sure if they will get you to .002 though.

Basically, here are your choices:
1 buy a bunch of different bearing brands and series of bearings which can get expensive.
2. Check the main housing bores and line hone to the minimum spec. That will generally tighten you up .0005".
3. Have your current bearings coated which will gain you about .001-.0015" but the coatings and application are often inconsistent.
4. Have the crankshaft ground to the correct size to allow -.010" bearings to be used with the desired clearance

I have no idea what your plans are with this engine, but IMO, .002 is very tight on the mains unless the line hone and crankshaft are absolutely perfect. You will need 5W-30 racing oil also running that tight. It can be done but your window for marginal machining is really small.

If it's a drag race engine, I would be OK with the clearance you have. Good luck with the build.

The math will be as advertised. 001 total

Send them in and get coated and you will get your .001. Calico. I know they do rod bearings.

The above is the best way to go about this and not waste hard earned money and lost race days!

I've used Calico numerous times. They have a std and thick coating, the thick coating will tighten up clearances 0.007"-0.001".

My clearance from aft to front are .0022,0025,0025,0023,0033 the front bigger clearance may help the pending load from pulleys.or should i get it coated

FM 4040M1 for 3" main

https://www.summitracing.com/parts/slp-4040m1

I don't see .001" tighter listed for 3.25" main.

As Mgarblik said, make sure the main housing bore is in spec and the crank journal is on size. You don't want to use an undersized bearing to crutch a separate issue.

Interesting that you have such a variation from front to back on your mains. I wouldn't worry about .0033 but I think .0022 is a little tight for a main bearing.

I think you will be fine with those clearances for a street car .0022 is a little tight for a race application.