Topic: Normal crankshaft wear?

[sammon287]

I'm not sure wear is the right word. I'm rebuilding a '76 750A with @18,000 miles on it. The two outermost journals on the crankshafts have marks perpendicular to normal rotational scoring. They don't catch a fingernail, but can be felt, more as a low spot. The related bearing shells don't show any unusual wear. The marks are in line with each other at opposite ends of the crankshaft and are also aligned with the #1 and #4 crank pins. Anyone see this before? Could it be from the manufacturing/balancing process? I'd rather not get the crank turned since I already have new bearings and I've spent enough already. Explanations/suggestions are welcome. See attached pics.

[sammon287]

more pics

[sammon287]

more pics

[bryanj]

Looks like impact damage to me, would never have left the Honda factory like that and you cant regrind it(turning is way too inacurate and rough), undersize shells do not exist.
The A model cranks are different as they use a hy-vo chain as primary.

[sammon287]

I thought I remember hearing that the crank can't be ground. The crank has been wrapped in saran wrap and sitting on a workbench since it was removed. No-one has access but me and it didn't get banged around. What's weird is that the marks are indexed to each other and the #1 and #4 crank pins. I'm not sure if I want to knock them down with some crocus cloth or just assemble it as is and hope for the best. I wonder what the risk of a slight low spot would be if 98 percent is still concentric. All the other main journals are perfect.

[754]

wont hurt to polish with crocus cloth. check the oil holes on the journal, if they are nodded its been out before.

[Tracksnblades1]

287,
 
Can you fell it with your finger or finger nail...?
Can you measure it with a micrometer....?
Is it plastic gauge residue...?  Engine oil will dissolve it....
Is it a solvent stain...?

+1 on 754

wont hurt to polish with crocus cloth. check the oil holes on the journal, if they are nodded its been out before.

[sammon287]

I know it looks like plasti-gage. It's not. The old fingernail and an oily rag have no effect. The perpendicular orientation and alignment with each other do make it look like that. It doesn't catch a nail like a burr would, but it can be felt barely. I guess a little polishing is my only choice.

[sammon287]

800 grit cloth too much? I have finer papers. I don't want to remove material.

[bryanj]

Yes too much and use lots of oil on the paper

[Tracksnblades1]

800 grit cloth too much? I have finer papers. I don't want to remove material.

Google polishing rod/main journals.....

Machine shops back in the day had a small narrow belt sander mounted on the crankshaft grimder's tool post and the sand paper was fairly rough.  The belt sand sanded the crank while the lathe slowly rotated the crank. The Best claimed way, was opposite of crank rotation because of the "fish scales" created by the grinding process.  I've seen old mechanics use the shoe string method afterwards to achieve a mirror finish.

Hand polishing with 1000 or crocus, I'll bet you'll work up a sweat just to remove .0002 ten thousands. The rule has always been, if you can feel it, you can measure it.

[pjlogue]

Don't use sandpaper.  Use Crocus cloth.  You want to polish the spot.  Even 1000 grit sandpaper is to coarse. 

-P.

[maxheadflow]

Is there more than 1 mark on the journal. Maybe someone spun it in a lathe?  Personally I'd use 600 wet and dry.  I wouldn't worry if it dont polish out.

[sammon287]

Don't use sandpaper.  Use Crocus cloth.  You want to polish the spot.  Even 1000 grit sandpaper is to coarse. 

-P.

800 grit crocus cloth was the finest I could find

[HondaMan]

I would attempt to measure them. If they are a divot, I'd ignore them and run the engine. If they are raised, they can scrape the bearings, in which case they need to be polished down using 4000 grit or crocus cloth, and gingerly.

[bryanj]

Try a body shop 2000 grade wet and dry is available

[pjlogue]

Don't use sandpaper.  Use Crocus cloth.  You want to polish the spot.  Even 1000 grit sandpaper is to coarse. 

-P.

800 grit crocus cloth was the finest I could find

You can find 1000 grit crocus cloth here:  https://www.imperialsupplies.com/item/0713980   There is a huge difference between wet-dry sandpaper and crocus cloth.  Wet-dry is usually silicone carbide.  Crocus cloth is iron oxide.  Silicone carbide is extremely hard and abrasive.  Iron oxide is harder than steel but no where near silicone carbide.  I would do as HondaMan suggested and mic. it.  It probably will show as a slight low spot.  I would also mic. each side of the spots.  If it is a ding from impact you will see a slightly raised spot to each side of the bark.  My guess it is from some type of corrosion.  If the engine was shut down for a long period of time and acids or moisture from combustion were in the oil it could have caused the marks.  Given that they both are on the same spot rotationally on the crank it is hard to imagine it being caused from being dropped.

-P.

[maxheadflow]

I find it odd that some think the surface needs to be polished to a glass like surface.  Go for it if it's what you want.  For me I like to see a slightly rougher surface.  It does a couple things to help during break in. First it retains oil / assembly lube to keep the surface from drying out. Second it provides a rougher constant surface finish that allows parts to wear in. No part it perfectly straight.  This allow clearances to become more consistent in fit.  Not allowing for this can create high contact pressure points which can cause galling. It's one of the reasons why the first oil change is so important. Parts don't even have to be new but simply miss matched.   

I agree that once any high spots are removed, the cranks is likely fine. Might lose the slightest bit of oil pressure but there is still plenty of surface to carry the load. This is not a roller bearing race.

[maxheadflow]

https://www.enginebuildermag.com/1998/09/crankshaft-polishing-make-sure-the-journals-on-the-crankshaft-are-properly-polished/

[pjlogue]

The crank journals are case hardened.  The crank bearing shells are soft compared to the crank journal.  Of the two, you would want any roughness in surface to be on the softer piece and the harder piece to be as polished as possible.  The crank will round over the high spots on the softer bearing shells without much harm to either piece.  If the rougher surface was on the harder crank, there would be appreciable wear in the softer bearing shells and this wear would continue for quite some time. 

-P.

[maxheadflow]

While you can harden them, don't think that they typically are.  No reason to.   Do you have a reference?

[pjlogue]

While you can harden them, don't think that they typically are.  No reason to.   Do you have a reference?

I think I read this in HondaMan's book and the hardness penetrating to about 0.005"   I may be wrong in the cranks being hardened, however, the crank material is going to be harder than the bearing shells.  One of the materials (either the journal or the shell) has to be soft enough to embed any foreign particles so it avoids grinding the particles.  You naturally make the shells (replaceable) softer than the journals on the crank.  https://me-mechanicalengineering.com/desirable-properties-of-bearing-materials/

-P.

[maxheadflow]

While you can harden them, don't think that they typically are.  No reason to.   Do you have a reference?

I think I read this in HondaMan's book and the hardness penetrating to about 0.005"   I may be wrong in the cranks being hardened, however, the crank material is going to be harder than the bearing shells.  One of the materials (either the journal or the shell) has to be soft enough to embed any foreign particles so it avoids grinding the particles.  You naturally make the shells (replaceable) softer than the journals on the crank.  https://me-mechanicalengineering.com/desirable-properties-of-bearing-materials/

-P.

I don't see any reference to hardening of the crank in Paris' book.  If you have a page number that would be good. Only place I found referenced to polishing was small rod ends with 400 grit emery.

You're link is good for bearing material but says nothing about shaft finish.

Again, the link I provided talked about using 320-400-600 grit to motor polish a crank after grinding.  Using 600 wet and dry by hand is not that aggressive.

[PeWe]

A slightly used wet grit 400 or 800 will not be that sharp as when new.

[pjlogue]

While you can harden them, don't think that they typically are.  No reason to.   Do you have a reference?

I think I read this in HondaMan's book and the hardness penetrating to about 0.005"   I may be wrong in the cranks being hardened, however, the crank material is going to be harder than the bearing shells.  One of the materials (either the journal or the shell) has to be soft enough to embed any foreign particles so it avoids grinding the particles.  You naturally make the shells (replaceable) softer than the journals on the crank.  https://.com//

-P.

I don't see any reference to hardening of the crank in Paris' book.  If you have a page number that would be good. Only place I found referenced to polishing was small rod ends with 400 grit emery.

You're link is good for bearing material but says nothing about shaft finish.

Again, the link I provided talked about using 320-400-600 grit to motor polish a crank after grinding.  Using 600 wet and dry by hand is not that aggressive.

In Mark's book, page II-23  While discussing the crank journals..."the journals seem to be deeply hardened"  Granted this is not the same as saying the crank journals are case hardened or quench hardened.  On page II-25 Mark makes note that the bearing shells being purposefully made soft to embed foreign material.  Given that the oil film in the bearings is on the order of 1-300 microns.  On a hot engine the film will be on the low end of this.  I would not use any aggressive sandpaper on the journals where you run the risk of causing cuts greater than the oil film thickness.  even 600 grit (13-16 micron) wet dry paper will remove material quickly and for each 1/2 thou. you take off the journal you have increased the clearance of the bearing by 1 thou.  If you think about the journal-bearing and the soft bearing vs the harder journal it makes sense to want the journal polished and any oil retaining groves to be in the softer bearing surface.  Hard very smooth surface will not wear into the softer bearing and the soft bearing will not wear the hard journal.

I rebuilt my cylinder heads for my GL1000 and turned the camshaft in my lathe and used crocus cloth to polish the journals and cam lobes.  I carefully measured them before, during and after polishing and I could not detect any removal of material.

-P.