[mike76]

I have a score on one of the rod journals and am thinking on having the rod journals taken down .010" and leaving the mains alone. Will doing this require me to have the crank re-balanced? It was balanced a few yrs. ago and am using all the same reciprocating parts. Thanks, Mike
PS: The score was a result of dirt in one of the rod journal holes that caused a score around the whole journal. Can I get by polishing the score if that journals' dimensions are identical across the journal? The marks and pits in the pic is only oil and the journal is very smooth other than the score. Just wondering...

[hurryinhoosier62]

Mike,

To polish out a defect that deep would be difficult if not nearly impossible. The chances are you would end up with way too much taper in the journal. Yes, you will have to re-balance. Anytime you remove material from a crank AFTER it has been balanced it must be re-balanced. Be sure to have your crank grinder make sure the throws are in stroke.

[lust4speed]

From the looks of the picture, if it were mine I'd bolt it back together and run it. Just a little extra area to hold additional oil. Also, I don't rebalance when only cutting the crank. Figure that the weight removed from the rod journal is pretty much replaced by the thicker bearing. Yeah, I know I'm cheap...

[mike76]

Originally Posted by lust4speed

From the looks of the picture, if it were mine I'd bolt it back together and run it. Just a little extra area to hold additional oil. Also, I don't rebalance when only cutting the crank. Figure that the weight removed from the rod journal is pretty much replaced by the thicker bearing. Yeah, I know I'm cheap...

This statement reads my mind exactly. As long as the scored surface has the same diameter as the rest of the journal I'm thinking no real harm. Just replace the bearings and double check the clearances for any issues. But I had to ask since this is a 500hp street/strip deal.

[hurryinhoosier62]

Mick,

HOW MANY cranks have you ground or polished? There's CHEAP and there's NUTS. Rule of thumb...IF you can hang a finger nail in the groove, it's TOO DEEP.

[NeighborsComplaint]

I would cut the rod journals .010 but have them check the mains for taper and scoring also. A .010 cut should not require a rebalance for street usage. I have seen guys just turn the one rod journal undersized and use one undersize bearing. In theory, the amount you remove from the crank is replaced by the thicker bearing shell on the undersize bearing and balance is unchanged.

[hurryinhoosier62]

Originally Posted by NeighborsComplaint

I would cut the rod journals .010 but have them check the mains for taper and scoring also. A .010 cut should not require a rebalance for street usage. I have seen guys just turn the one rod journal undersized and use one undersize bearing. In theory, the amount you remove from the crank is replaced by the thicker bearing shell on the undersize bearing and balance is unchanged.

IN THEORY. Can you guarantee that both bearings weigh the same and will NOT change the bobweight on that cylinder? Answer: NO, not unless you weigh everything involved. I also realize the specs I use for balancing (less than .5 gram) is a little tighter than what most shops use.

[racegto65]

Originally Posted by lust4speed

From the looks of the picture, if it were mine I'd bolt it back together and run it. Just a little extra area to hold additional oil. Also, I don't rebalance when only cutting the crank. Figure that the weight removed from the rod journal is pretty much replaced by the thicker bearing. Yeah, I know I'm cheap...

X2 Just polish it to make sure there are no rough edges.
I have balanced many crankshafts and not seen enough difference
after a regrind to cause issues.

[mike76]

You guys know a lot more than I do here and I am just trying to understand not have a difference of opinion. This is my question:
If, in measuring across the journal in question both with a mic and plastigage and BOTH tell me that there is no deviation across the journal( scored area vs smooth area) then where is my problem? I know that when one scores a journal it is customary to re-grind. But why does my situation call for a total re-grinding? I mean does the score cause a fracture point on the journal??? Is the journal weakened?...... What?? This rebuild has only 3700 miles on it and the score has probably been there since initial start-up . The other rod and all the main journals are fine. Took engine apart because my crank end play grew from .007" to .011" and for no other reason!

[NeighborsComplaint]

The reason it is recommended that you machine the scored journal is that the "scar" may not be perfectly concentric to the rotation of the crank, the edges may have a very slight ridge and the width of the score may not be uniform all the way around the journal. Any and all of these conditions will wear away your new bearing. How long his takes depends on the condition.

In theory the rod rides on a wedge of oil between the bearing and the rod journal and it shouldn't matter, but startup and shutdown will shorten the life of the bearing. If you don't mind a do-over in the near future, you can roll the dice and just polish the journal. It could last years or months.

[hurryinhoosier62]

Originally Posted by NeighborsComplaint

The reason it is recommended that you machine the scored journal is that the "scar" may not be perfectly concentric to the rotation of the crank, the edges may have a very slight ridge and the width of the score may not be uniform all the way around the journal. Any and all of these conditions will wear away your new bearing. How long his takes depends on the condition.

In theory the rod rides on a wedge of oil between the bearing and the rod journal and it shouldn't matter, but startup and shutdown will shorten the life of the bearing. If you don't mind a do-over in the near future, you can roll the dice and just polish the journal. It could last years or months.

I'm STILL of the opinion to remove a score like the one pictured with polishing could lead to too much taper in the journal. You're going to have to get fairly aggressive with the polishing. Even with micropolishing, you can induce taper. We used to polish aircraft crankshafts because you couldn't grind them undersize. The OEs provided .001,.0015 and .002 oversize bearings for this reason. Additionally, the OP doesn't clarify whether his mics are set of thousandths (.001) or ten-thousandths (.0001). Yes, cracking CAN occur in a journal that has been scored, but the only cases where I've seen this happen is where the journals were severely over heated (blued) and scored from lack of proper lubrication.

[llwta76]

The OP says that the mic shows the SAME READING across the journal. I can't imagine a mic w/an accuracy in the ten thousands for deviation is necessary here. I've hand polished cranks(@ home) w/small wear ridges in them and operated them for many thousands of rough street miles. I say it isn't necessary as long as there is no swelling of material @ the score area and there are no sharp areas above the journal.

[70 bird]

If this is not a high rpm motor I would just lightly polish the area and run it.

[FrankieT/A]

Originally Posted by 70 bird

If this is not a high rpm motor I would just lightly polish the area and run it.

What he said!

[lust4speed]

Originally Posted by hurryinhoosier62

Mick,

HOW MANY cranks have you ground or polished? There's CHEAP and there's NUTS. Rule of thumb...IF you can hang a finger nail in the groove, it's TOO DEEP.

Zero. I'd have to use my Harbor Freight hand grinder.

My favorite machine shop uses Castillo Crankshaft Services which has a great reputation for doing custom work. Many of the cranks I send in will have each journal individually cut to size to obtain whatever clearance I plan on running. In this case, the scoring occupies a small percentage of the bearing width, and the grooving is really minimal. I wouldn't hesitate to run it.

I do agree that anything other than a light polish will do much more harm than good. Besides introducing a taper, excess polishing is going to egg shape the journal.

[PONTIAC DUDE]

Balanced tons of combos. If you're turning down the rod journals .010 or so. and not a high rpm race engine. You won't have to rebalance.

[PONTIAC DUDE]

Balanced tons of combos. If you're turning down the rod journals .010 or so. and not a high rpm race engine. You won't have to rebalance.

One could get anal and do it, but will not notice a difference.

[hurryinhoosier62]

Originally Posted by PONTIAC DUDE

Balanced tons of combos. If you're turning down the rod journals .010 or so. and not a high rpm race engine. You won't have to rebalance.

One could get anal and do it, but will not notice a difference.

Guilty as charged, Ken. I take NOTHING for granted. Any time I have, it has bitten me.

[hurryinhoosier62]

Originally Posted by llwta76

The OP says that the mic shows the SAME READING across the journal. I can't imagine a mic w/an accuracy in the ten thousands for deviation is necessary here. I've hand polished cranks(@ home) w/small wear ridges in them and operated them for many thousands of rough street miles. I say it isn't necessary as long as there is no swelling of material @ the score area and there are no sharp areas above the journal.

As a retired ASE master engine machinist, ten thousandths make a BIG difference. If you are running a .0018-.002 rod bearing clearance and the rod bearings you use are .0002 thicker, your rod bearing clearance just dropped to .0016-.0018 instead of .0018-.002. I was involved in a warranty situation where the bearings supplied were .0002-.0003 thicker than the bearings used in the original spec. The engines were fine during assembly and on the test stand, but locked up in service. 48 engine destroyed due to .0002-.0003 more material. Do you still think ten thousandths don't make a difference? BTW......EVERY mic I own is graduated in ten thousandths. If you were to buy a Sunnen gauge set, they are graduated in ten thousandths.

[llwta76]

Originally Posted by hurryinhoosier62

As a retired ASE master engine machinist, ten thousandths make a BIG difference. If you are running a .0018-.002 rod bearing clearance and the rod bearings you use are .0002 thicker, your rod bearing clearance just dropped to .0016-.0018 instead of .0018-.002. I was involved in a warranty situation where the bearings supplied were .0002-.0003 thicker than the bearings used in the original spec. The engines were fine during assembly and on the test stand, but locked up in service. 48 engine destroyed due to .0002-.0003 more material. Do you still think ten thousandths don't make a difference? BTW......EVERY mic I own is graduated in ten thousandths. If you were to buy a Sunnen gauge set, they are graduated in ten thousandths.

I admit that the tighter the clearances you shoot for ( as in the example you state) the more critical diviation becomes. But I was referencing the OP and my own experiences in running .0025" +/- bearing clearances. I would be uncomfortable running any bearing clearances as tight as those you mention. After all we're talking about Pontiac street/ strip stuff here. Again... he states that there is NO deviation in journal diameter and no change shows up when using plastigage also. I do admit it's great to be able to machine to within 1 or 2 ten thousanths when doing bearing clearances but I have never found it necessary in any of my own experiences.