Bearing clearance, 2056 build #2 Options

[Chad911sc]

So I got my crank back from a different machine shop this time, and they turned it down .010 on the mains to clean up my out of roundness. I rotated it several rotations on an V-block and had no deviation. My new oversized bearing came in yesterday, and I’m checking clearances now. I plastigauged the middle bearing and I have what looks to be .0018 of clearance. Is this acceptable? Here is the pics to double check me.
My rods were right at .001, so I’m good there.

[rfinegan]

.001 feels a little tight to me on the rods. Careful

[mepstein]

I would have the machine shop do the measurements. They have measuring tools that are much better than plastigauge.

You really want to measure at every bearing. Just measuring one and hoping the others are the same can get you in trouble.

[Chad911sc]

@rfinegan
I didn’t have the rod journals turned, they were right on spec. The rods were bought new from LN engineering, and they prepped and sized them before shipping. The engine ran for around 3 hours the first time, and the bearings upon disassembly were fine. They were definitely reusable, but I bought new ones anyway.

@mepstein
The machine shop did mic each journal and they were all right on spec. I then rechecked them when I got home and obtained the same results. From what I’ve read, the clearance should be .002 on the middle bearing because it takes the load of 2 rods. Mine looks like it’s a hair tighter, so I was wanting to know if that is acceptable, or do I need to polish t a bit and try to get it right at .002

[Superhawk996]

From what I’ve read, the clearance should be .002 on the middle bearing because it takes the load of 2 rods. Mine looks like it’s a hair tighter, so I was wanting to know if that is acceptable, or do I need to polish t a bit and try to get it right at .002

Take with grain of salt. Clearance advice is like oil - it’s sort of a religion. The advice is worth what you paid.

Peter Russek repair guide lists crank main clearance for #1 & 3 as .002”-.004

#2 as 0.0011” - 0.0035”

Personally I like .002” as the target.

But trying to measure to ten thousandths with plasticgage is not realistic.

As was stated previously, I put more faith in measuring OD with a micrometer and bearing bore ID (with case fully torqued) with a bore gauge and doing the math.

I would base any next steps on assembled drag with only a light coat of 20wt oil and see how much drag is on the crank and then we are down to subjective feel.

If you truly are at 0.0018” plan to run something lighter than the 20W-50 guys seem to love or you’ll be asking for problems IMHO.

[930cabman]

I have always liked the "assembled drag" as Phil has mentioned. Unless one has the correct gaging tools there are variables. ie, checking the case for straightness and dimensions can only be accomplished with fancy tooling generally not available to many of us garage hacks. Checking a crank is more straightforward.

Hope it goes correct for you this time

[Chad911sc]

10-4
I will put the bearings in dry and torque the case down today and get my exact measurements on the bearings. I already have my exact measurements on the crank journals from the machine shop that I double checked at home with my mic and post those today.