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#1
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crank regrind question
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... |
#2
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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.
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“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
#3
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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...
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Mick Batson 1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon. |
#4
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Quote:
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#5
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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.
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“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
#6
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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.
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#7
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__________________
“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
#8
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I have balanced many crankshafts and not seen enough difference after a regrind to cause issues. |
#9
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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! Last edited by mike76; 03-13-2014 at 12:18 PM. |
#10
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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. |
#11
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__________________
“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
#12
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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.
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#13
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If this is not a high rpm motor I would just lightly polish the area and run it.
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#14
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What he said!
__________________
1978 Black & Gold T/A [complete 70 Ram Air III (carb to pan) PQ and 12 bolt], fully loaded, deluxe, WS6, T-Top car - 1972 Formula 455HO Ram Air numbers matching Julep Green - 1971 T/A 455, 320 CFM Eheads, RP cam, Doug's headers, Fuel injection, TKX 5 Spd. 12 Bolt 3.73, 4 wheel disc. All A/C cars |
#15
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Quote:
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.
__________________
Mick Batson 1967 original owner Tyro Blue/black top 4-speed HO GTO with all the original parts stored safely away -- 1965 2+2 survivor AC auto -- 1965 Catalina Safari Wagon. |
#16
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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.
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#17
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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. |
#18
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Guilty as charged, Ken. I take NOTHING for granted. Any time I have, it has bitten me.
__________________
“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
#19
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Quote:
__________________
“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
#20
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