Is there a "how to.." for crank measurement, and bearing verification? Options

[malcolm2]

I am gonna make a 2 liter from my 1.8. So I have a refreshed 71mm crank that I have been told has been ground to -0.010.

I measured as best as I can with a digital mic and got about 59.66 on the mains and 49.65 on the rod journals.

Where can I find the STD specs and ranges ? were they 60 and 50, respectively?

Since I know nothing about this crank, how can I verify the 71 mm measurement?

[malcolm2]

OK, maybe not the super duper accurate tools but I feel better after these measurements. They are the Mitutoyo brand... so this is what I got.

#1 main is 0.0072 under
#2 main is 0.0076 under
#3 main is 0.0072 under
#4 main is 0.00925 under

Rod journals are all 0.0084 under

So I had already bought some 0.010 under (0.25mm) main bearings, so I am gonna get some plasti-gauge and see where the clearance ends up.

What are the thoughts of the group??

[Superhawk996]

OK, maybe not the super duper accurate tools but I feel better after these measurements. They are the Mitutoyo brand... so this is what I got.

#1 main is 0.0072 under
#2 main is 0.0076 under
#3 main is 0.0072 under
#4 main is 0.00925 under

Rod journals are all 0.0084 under

So I had already bought some 0.010 under (0.25mm) main bearings, so I am gonna get some plasti-gauge and see where the clearance ends up.

What are the thoughts of the group??

I assume this is the .010" under crank we are talking about. If that is correct, it sounds to me like you're tightening the micrometer too much. The crank from GA004310 was definately AT LEAST 0.0100" undersized and was running in 0.010" undersize bearings when I tore it down. The clearnace would but super "tight" in 0.010" undersize bearings. Micrometers can be a bit fickle to learn to use if you are not used to using them. Mitutoyo usually have a small ratchet knob to help set the "feel" and keep from overtightening.

Three suggestions.

1) Make sure you're only tightening the micrometer until you have only the slightest friction feel when the Micrometer slips off the journal. Keep measuring until you're getting repeatable measurements +/- 0.0001". It's definately a feel thing. Practice measuring a human hair if you have to. You should be able to measure the hair and pull it out of the micrometer without it breaking but yet still feel the friction on the hair.

2) If you are consistently coming in above 0.010" undersize, then check the micrometer calibration. They should have a calibration gage. 1", 2", 3" etc. whatever is appropriate to the range of the Micrometer. Make sure the micrometer is calibrated to that gauge meaning that if for example it is a 2.0000" gauge block, that the micrometer comes in right at 2.0000". Google how to do that calibration if not familiar, likewise there should be a very small special wrench with the micrometer to do this. If it missing don't even try.

3) If you can't seem to get the feel and/or you don't have calibration gage blocks, then have a machine shop measure as Mark suggests. No harm and they will probably do it for free.