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Thread: Why grind the crank? & What wt. oil to use?

  1. #1
    1899
    Been looking for awile on the search engine, Im just curious. why do some builders grind the crank? Ive got a 455. Im currently running std. rod and main bearings. Also On the stand, im running 5W-30 and im getting 55Lbs cold. But when running hard on the water it could change things a bit.what weight oil should I run on a freshly built motor?

  2. #2
    Senior Member
    Join Date
    Feb 2009
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    1,907
    I do not have freshly rebuilt engine but I've always been told to run straight 50 and it did make a diffrence from the 5-30
    beerjets .02

  3. #3
    SmokinLowriderSS
    Mains on a 455 will often get ground because they are so large that at high RPM's the surface speed of the steel in the oil film at the bearing gets very high. Grinding that circle to a smaller diameter reduces the shear forces which reduces oil heating.
    My taylor ran 10-40 oil for decades, no problem. I tended to run 20-50 castrol, still no problems, Big end bearings were worn out when I took her down last winter, but was 27 years old, no damage. She now runs 10-50 Syntech pure synthetic from Castrol. Modestly modded 454, about 400 genuine HP on the new headers over old logs.

  4. #4
    Senior Member
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    Feb 2009
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    2,626
    ...... Im just curious. why do some builders grind the crank? ....
    It's pretty simple, really. The crank journals need to be round and need a smooth surface. Over time, the journals do go out of round and can develop taper. The surface of the journal can develop scratches and other blemishes. Would you want to put something like this back in your engine? The only way to correct any imperfections of this sort is to re-grind the crank down to the next size. Re-grinds are done in increments of .010".
    Hopefully any "builder" who doesn't regrind a crank has documented that it has no physical defects.
    Mains on a 455 will often get ground because they are so large that at high RPM's the surface speed of the steel in the oil film at the bearing gets very high. Grinding that circle to a smaller diameter reduces the shear forces which reduces oil heating.
    A stock regrind isn't going to do anything to help that problem. The Olds455 has much larger main and rod journals than, say, a BBC at 3" and 2.5", respectively. The BBC is 2.75 and 2.2" for mains and rods. If you wanted to reduce ROD bearing speed you'd need to regrind to a much smaller size(like the BBC's 2.2"), necessitating the use of custom rods. Nothing you can reasonably do to reduce MAIN journal size.

  5. #5
    1899
    I thought you polished the crank to remove any imperfections. Ok got it.

  6. #6
    Senior Member
    Join Date
    Feb 2009
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    In some cases you might get by with polishing, but those imperfections had better be very small. You can not polish a crank journal back to "round". Grinding cranks is a very common practice.

  7. #7
    H2OT TIMES
    I am told by more than one guy, who knows more about Olds than I, that it is critical to reharden the Olds crank after it is ground. Evidently there are several ways to do that and I'm told to use what ever methode you happen to prefer, but be sure you do it.

  8. #8
    SmokinLowriderSS
    Thx for the clarification Oldsquirt. I was just not thinking of the "clean-to-round" on a rebuild and was thinking of the journal size change work you described for the reason I posted. You covered both well.

  9. #9
    moneysucker
    I would not recomend 50 wt Olsd 455s are known for not being able to drain back into the pan fast enough already and starving the bottom end of oil. I used 20 50 in mine back in the day with a 10 qt pan. I would stick with 10 40 or 20 50 a multi wt oil is probably better in this application unless there are oiling mods done then your builder would have told you what oil you should use. Good luck with the boat.
    Cy

  10. #10
    TIMINATOR
    ***boat Mag. April issue. BIG OLDS ARTICLE. Answers all the questions. TIMINATOR

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