BP - N/A - Endurance Bearing Clearances
 

I'm putting new bearings in our motor that lost oil pressure, its my first time doing this, and I was hoping the wisdom of the forum can make some recommendations.

The crank was magnaflux'ed previously and looks good. We lost oil pressure (Pressure relief valve stuck) and we beleive we caught it almost immediately. All bearings looked great, except the #4 rod, which had some copper showing. After disassembling, the crank journals feel great and we seemed to avoided any damage. I plan on installing new bearings and re-install the motor.

The crank measures as follows:

NOSE
MAIN 1: 1.9660
MAIN 2: 1.9662
MAIN 3: 1.9660
MAIN 4: 1.9660
MAIN 5: 1.9662
REAR

ROD 1: 1.7688
ROD 2: 1.7688
ROD 3: 1.7690
ROD 4: 1.7694

All journals are round to 50 millionths - Measured with Mitutoyo Micrometer


Last time I believe I ordered all STD ACL bearings, EXCEPT the #4 rod we used 0.025mm bearings, however I do not recall if they were + or - bearings.

What are your thoughts on the bearings I should order to maximize our reliability and what oil should we run?

We currently make ~145 RWHP

TIA!

I believe you need to order the bearings first, then measure the ID of the installed bearing then subtract from that the OD of the corresponding journal on the crank. This gives you your oil clearance.

So you put a larger bearing on your largest rod? Use plasti gage and measure oil clearance, should be .0015-.0025. I ran .002 for a full season at 150, no issues.

but, if your crank doesn’t look like a god damn mirror, send it out to be ground for .25 over.

Get the journals polished

Do you guys recommend anyone in particular for crank refinishing? I've bought half a dozen cranks to find a good one because our engine shop said it's not worth refinishing. The crank we have now looks great with perfect journals, but I'd like to have a refinisher if we need one later.

Where are you and we can recommend a shop to send them out for grind, not refinish

Milwaukee, but I'm not opposed to shipping.

Just an update. I ordered ACL H, HX and 0.025 bearings for mains and rods. I started putting different combos in the mains and measuring with a mitutoyo bore gauge and referencing that with the same micrometer I measured the crank with.

I used ACL recommend tolerencing and all the mains. Based on measurements I used a combo of STD(H) and 0.025 bearings, except one which I used STD(H)/STD(H).

Rods were the same story.

The crank looks good but I touched up two rod journals with 1500 grit and when done remeasured. It didn't even change a tenth.

Crank is now back in, everything torqued and stretched to spec.

I'm fortunate that I have some pretty high end measuring equipment but it was still alot of careful patient work to make everything perfect.

any chance oversized bearings were used?