When to Leave Well Enough Alone?

[Dan1950]

I spent the afternoon polishing the rod journals of my crank. Worked my way through 400, 600, 800 and 1000 grit wet of dry paper. The journals look great. After the polishing they mic'ed out at 1.7495" on the drive side, 1.7496" on the timing side. .0005" and .0004" undersize respectively. The micrometer was calibrated just before the measurements were taken. I came up with exactly the same dimensions that a local machinist found when I first tore down the crank.

My concern is that if I turn someone loose on my crankshaft to grind for .010" undersize shells, I might end up with worse than I have now. I feel like a new set of inserts in the rods will result in a long service life.

 

[Stephen Hill]

How do your measured dimensions compare with the permissible range of wear tolerances?

 

[concours]

Dan, test it with new standard shells & plastigage.
Pretty sure you'll be in the mean of the range.

If I'm wrong, you've only sacrificed a few bucks (shells)

Based on my observation/experience.


JMWO

 

[lcrken]

Stock crank is 1.7500" - 1.7505", and first undersize is .010", or 1.7400" - 1.7405". . Yours are 1.1745" and 1.1746" ? Something wrong here.

Ken

 

[Dan1950]

Dan, test it with new standard shells & plastigage.
Pretty sure you'll be in the mean of the range.

If I'm wrong, you've only sacrificed a few bucks (shells)

Based on my observation/experience.


JMWO

I checked the shells that were in service and had just under .002" clearance. The shells did appear to have some slight wear present.

 

[Dan1950]

Stock crank is 1.7500" - 1.7505", and first undersize is .010", or 1.7400" - 1.7405". . Yours are 1.1745" and 1.1746" ? Something wrong here.

Ken

As stated, .0005" and .0004" undersized.

 

[lcrken]

If you actually meant to say 1.745" and 1.746", then your journals are already ground to .010" undersize, and are worrn another .004 - .005" undersize, not .0005" and . 0004". The factory allowance for wear is .0015" ovality, and you are well past that. Sounds like time for a re-grind to me.

Ken

 

[Dan1950]

If you actually meant to say 1.745" and 1.746", then your journals are already ground to .010" undersize, and are worrn another .004 - .005" undersize, not .0005" and . 0004". The factory allowance for wear is .0015" ovality, and you are well past that. Sounds like time for a re-grind to me.

Ken

Sorry values should read 1.7495 and 1.7496. .0005 and .0004 undersize. 1/2 of one thousandth and .4 of one thousandth. There isn't any ovality.

 

[lcrken]

OK. That sounds more reasonable. And I had the stock spec a little wrong. It's not 1.7500" - 1.7505". The correct spec is 1.7504" - 1.7509". In any case, your crank appears to still be under the allowed .0015" wear spec, so you should be fine with just a new set of standard shells.

Ken

 

[concours]

The replacements I purchased were a bit on the snug end of the spectrum.

I checked the shells that were in service and had just under .002" clearance. The shells did appear to have some slight wear present.

 

[Dan1950]

OK. That sounds more reasonable. And I had the stock spec a little wrong. It's not 1.7500" - 1.7505". The correct spec is 1.7504" - 1.7509". In any case, your crank appears to still be under the allowed .0015" wear spec, so you should be fine with just a new set of standard shells.

Ken

Having trouble transposing Vernier micrometer reading to paper. Easier with digital I guess

 

[htown16]

Use Plastiguage to check the clearance on the new shells. Use the old rod nuts for the check then install new ones.

 

[Dan1950]

Use Plastiguage to check the clearance on the new shells. Use the old rod nuts for the check then install new ones.

That's my plan.

 

[Dan1950]

Use Plastiguage to check the clearance on the new shells. Use the old rod nuts for the check then install new ones.

New standard shell inserts on the crank journals Plasti-gaged between .001"and .0015." clearance.

 

[htown16]

I'd probably go with that, especially if closer to .001 than .0015.

 

[marshg246]

I spent the afternoon polishing the rod journals of my crank. Worked my way through 400, 600, 800 and 1000 grit wet of dry paper. The journals look great. After the polishing they mic'ed out at 1.7495" on the drive side, 1.7496" on the timing side. .0005" and .0004" undersize respectively. The micrometer was calibrated just before the measurements were taken. I came up with exactly the same dimensions that a local machinist found when I first tore down the crank.

My concern is that if I turn someone loose on my crankshaft to grind for .010" undersize shells, I might end up with worse than I have now. I feel like a new set of inserts in the rods will result in a long service life.

To answer the title of the thread - Now

 

[TomU]

Isn't 0005” within spec

And plastigauge is for people that don’t know how to use a mic

 

[concours]

Isn't 0005” within spec

And plastigauge is for people that don’t know how to use a mic

That, is a wildly inaccurate statement.

 

[htown16]

Shop manual says less than .001. .001 should have plenty of life left. .0015 is starting to push it a bit. Got to consider the intended use of the bike, occasional coffee shopper or touring and racing.
Re plastiguage, I've seen pro's use it. Seems like you have blown up a number of vehicles.

 

[kommando]

Shells are not round by design hence why plastigauge was developed. The shells have overstand to force them into contact with the big end to stop them from turning and a relief area on both ends where the overstand distorts to increase the thickness.