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 it passed the hammer test. very high pitched tuning fork ring. The 1.8 has an even higher ring and lasts longer. If that means anything... (IMG:style_emoticons/default/piratenanner.gif)

I have a set of micrometers coming from a workmate tomorrow. If he forgets, there is always Harbor Freight for $40.

With my method of measuring last night, I got a consistent 49.65 on all 4 rod journals.
Book says std is 49.97 - 49.98. That puts them at 0.33mm under which is -0.01299. Seams excessive.

More accurate measurements tomorrow, I guess.

So @Superhawk996 , did this crank ever run in it's current state? Or you took it out and polished it, but never installed?

[Superhawk996]

With my method of measuring last night, I got a consistent 49.65 on all 4 rod journals.
Book says std is 49.97 - 49.98. That puts them at 0.33mm under which is -0.01299. Seams excessive.

More accurate measurements tomorrow, I guess.

So @Superhawk996 , did this crank ever run in it's current state? Or you took it out and polished it, but never installed?

No the crank was never run in it's current configuration after the polish. I measured it roughly 0.010" under with my micrometer toward the high end of the tolerance. My machine shop said they did a light polish of .0001" - 0.0002". I cannot find any record of my having remeasured the crank after return because by then I had the standard size crank from Kevin. So in my mind, measure it, see what it is but more than likely it will need to to to 0.020" under to get it to be exactly on-size toward the high end of the tolerance.


Here's the bottom line: I never intended for this crank to go into an engine as-is and had assumed it would get plastigage'd for verification and/or taken down to 0.020" undersize.

I had no intention of representing this crank as being a a great crank. If this crank doesn't suit your purposes or you have any reservation about taking it to 0.020" under before use, I'll gladly refund the shippping cost that was paid to me. My only intention was to help a low buck rebuild with a free crank for the cost of shipping. The shipping cost is trivial and I would feel terrible if you tried to use this crank as-is and had a poor outcome. If you're OK to have it ground 0.020" under you could do that but given you have invested big$$ in the new heads, I can't see why you wouldn't try to find a good standard size crank.

Note: the tolerance on jounal diameters is only 0.02mm which is 0.0008". Eight ten thousands of an inch is the total tolerance between new and worn!

Quick note on caliper vs. micrometer accuracy for anyone that is interested in measurement of preciesly machined parts:

My 6" Mitutoyo digital calipers are accurate to +/- 0.001" with a resolution of 0.0005". This is not accurate enough to measure a crank with. Resolution is not the same as accuracy. If you play with a set of calipers like these and try to get a reading of 0.0006" it is not possible. The caliper will jump to 0.001".

https://www.mitutoyo.com/wp-content/uploads...8/07/15003A.pdf

My vernier micrometers are accurate to +/- 0.0001" with a resolution of 0.00005".

That is a comparison of 1/1,000th of an inch accuracy (larger than crank tolerance) vs. 1/10,000th of an inch (still 1/8 of the tolerance and not ideal). That is an order of mangnitude (x10) imporvment with the micrometer. Digital micrometers can be even more accurate to within 1/20,000th of an inch. A micrometer is what you need to accurately measure the crank and I can only say I wish I had a set of digital micrometers but that is too much $$ given how infrequently I use them.