SBF- bearing clearance with calipers & 0.001 US bearings

[Caprimaniac]

After a oil pressure issue I have opened the engine & looked for clues. I have not found much, but I MIGHT have a crank cut a bit on the low side.

However- the measurements have been done with a regular digital caliper. All rod pins gave the same result (measured 90 deg & at two spots).

Rod pins 2.100" measured 0.03 mm smaller. That's 0.0011" This is an Eagle 3.47" stroke crank.

I put in some bearing shells in the big ends and tightened the bolts by grabbing the rods by my left hand and the wrench in my RH. So, not torqed to spec.

Using the same caliper measuring the inside diameter of the bearing, I found a 0.09mm (0.0035") clearance. Mind you; the bearings had some coating missing, as this was more or less worn off during the 4 mins of runtime for this engine.
The bearing thickness measured I HAVE NOT written down, but I think I remember 0.0453". How does that sound?

Well- First off- as the tools used for measuring and the rods not tightened to spec- does it mean anything at all?

I remember when test- assembling the rods, I got a SMEAR of the PLASTIGAUGE, hard to interpret- but I wrote it down as 0.0022" clearance.

Last; does anyone have a set of Clevite CB-1227H-1 (for a 0.001" US crank) lying around for sale?

I include a photo of the bearing shells. One other thing to note her; the UPPERS (upper in the photo too) showed more of loosing the coating/ more damage than the lowers. This might tell me something, too:

IMG_1309.JPEG

[mt-engines]

Use a micrometer

[dannobee]

Calipers are not the right tool for the job. There's a reason that a lot of machinists call them "very near" calipers.

Get a mic that measures in tenths of a thousandth.

[BCjohnny]

However- the measurements have been done with a regular digital caliper

It's almost impossible to get repeatable measurements you can rely on using such a method

A micrometer and 'tenths' bore gauge is what you need

Edit :

To add ....

The mic doesn't need to be anything special, as long as the anvils are parallel

You're only using it as a 'setting fixture' for the bore gauge (or more accurately bore comparator)

Even the cheapie online BGs give reasonably repeatable measurements, for a hobbyist

[BillK]

You simply cannot measure crankshafts or bearings with a caliper. Period.

The rods need to be torqued to specs to measure. Same with the mains.

The bearings don't look bad at all to me.

If you dont have the proper tools there is a quick way to check clearances that will at least let you know if you are close. I have only tried it on a main but I think it might work on a rod if you try. Take a .002" feeler gauge and put it between the crank and the main bearing as show in my picture below. Then torque the main cap. If you can pull the feeler gauge out then you know you have at least .002 clearance. If you cant pull it out then try a .001 and see what happens. If the .002 pulls out real easy try a .003" This will at least get you close. In my picture I dont have the feeler gauge all the way in between the bearing and crank. I just held it up there to give you the general idea. I had already torqued the caps on this engine and did not want to loosen them to show this method.

Feeler gauge clearance.jpg