Time to regrind the crankshaft right?

Dan Truax · Mar 19, 2019

8N crankshaft specs 2019 by Daniel Truax, on Flickr

Reading the FO-4 its time to regrind the crankshaft right?

Thanks...

Dan Truax · Mar 20, 2019

The more I read it seems I should renew the journals and go next undersize with the rod bearings?

Oh well time for bed...

TheOldHokie · Mar 20, 2019

(quoted from post at 04:33:51 03/20/19) The more I read it seems I should renew the journals and go next undersize with the rod bearings?

Oh well time for bed...

Crankpins for sure. The mains are much better but .003 out of round and taper would be too much for me.

Not to be rude but how much do you trust those measurements? You are showing numbers larger than factory new specification. My Clevite catalog says main journal tolerance new is 2.2480/2.2490 and crankpins are 2.0935/2.0945 Are you using a micrometer capable of tenths and not a caliper? Some people think calipers and micrometers are interchangeable. And if a micrometer have you calibrated it against a reliable standard? Absolute measurements are only as accurate as the calibration of the instrument.

Regardless it's going to go on the machine for the crankpins and as I said if it were me I'd have mains done as well. That will assure you of best possible oil clearances when it goes back together. It will go .010/.010 under and barring a crack still many, many years of service left in it.

TOH

Bob - MI · Mar 20, 2019

Great question and I fully agree with the micrometer vs caliper statements.

In my younger days I started a career in machining with a Gardner Denver plant and their standard was: any dimension with a tolerance of +/- .015 could be checked with a caliper. Anything less would be a micrometer or some sort of special gauging as required.

Dan Truax · Mar 20, 2019

Cheap chinese micrometer. I don't trust the overall measurement but for out of round and taper I trust it.

After every measurement I'd go back to zero and it would be off by .001".

Dan Truax · Mar 20, 2019

So do you recommend Magnafluxing the crankshaft too?

TheOldHokie · Mar 20, 2019

(quoted from post at 15:35:14 03/20/19) Cheap chinese micrometer. I don't trust the overall measurement but for out of round and taper I trust it.

After every measurement I'd go back to zero and it would be off by .001".

Sounds like an economy digital micrometer with .0005 resolution - should be fine for comparative work. My experience with digital instruments is even the expensive ones have a tendency to skip counts. Both of my Mitutoyo calipers have an issue with that.

I have a set of Taiwanese .0001 vernier micrometers. They seem to be as accurate as my Mitutoyo instruments but they also seem to need calibrated more often. The laser engraving on the barrel is also pretty faint and hard to read. Still well worth the $75 I paid for the 0-4" set.

I would definitely magnaflux the crankshaft and I would be surprised if that didn't come as part of the grinding service.

TOH

Dan Truax · Mar 20, 2019

OK, just stopped by my local machine shop. Head and block are in the oven. He doesn't grind crankshafts anyways.

So the expert in this county on grinding crankshafts is flakey and only works when he needs that cash so its off to the next county tomorrow morning...

ASEguy · Mar 21, 2019

Good call. You never regret doing the job right.

Time to regrind the crankshaft right?

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