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Old 08-23-2005, 05:15 PM
BigDawgsEatFirst's Avatar
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Crank Cutting

shop told me, 400 crank needs to be cut 30/30
rods/ mains.
that is cutting it close(LOL )
has anyone gone that far
is it safe,(to run)
motor is 400 .030 over bore (max rpm will be 6,500)
new crank is 179.00 standard/standard
to cut 75.00
I have heard of guys cutting cranks 20/20 that did not need to be cut for strength
Why ?

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Old 08-23-2005, 05:34 PM
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30/30..seen a few..personal i would not do it...new one is not that bad...plus with a new one ..it can be truned again when time comes time for a rebuild
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Old 08-23-2005, 05:48 PM
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Quote:
Originally Posted by 347mustang
30/30..seen a few..personal i would not do it...new one is not that bad...plus with a new one ..it can be truned again when time comes time for a rebuild
your right
I can pay now or
pay later............
( I just had to ask)
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Old 08-23-2005, 05:51 PM
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A crank properly ground to .030"-.030" is stronger than one poorly ground to .010"-.010". The difference in strength is minimal. It's the quality of the journal radii the determines the strength of the crank. Think of it this way. A 383 crank is a 400 crank with .200" groung off the mains. Don't see them breaking from being over ground. And the small journal SBC had rod journals .100" smaller than the larger journal.

tom
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Old 08-23-2005, 05:53 PM
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400 cranks are a bit thicker than most other sbc cranks. I have seen 20/20 on forged small journal cranks turn 7k and live. 30/30 on a 400 for passenger car/light pu duty would probably be ok.

I would get a new crank.
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Old 08-23-2005, 05:59 PM
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Thanks for replys
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Old 08-23-2005, 06:02 PM
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If you are going to spring for a new crank, consider getting an internally balanced one.

tom
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Old 08-23-2005, 06:20 PM
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Quote:
Originally Posted by machine shop tom
If you are going to spring for a new crank, consider getting an internally balanced one.

tom
Than
I can tell everyone it is a 350
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Old 08-24-2005, 11:05 AM
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So you guys wouldn't be interested in the .060 under SBC rod bearings I have AHH???
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Old 08-24-2005, 11:11 AM
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I've turned 400 cranks to 60/60 a bunch of times. Never had an issue. Be sure to deck the block to keep compression.
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Old 08-24-2005, 12:05 PM
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just a comment to ponder if worried about how much has been taken off of your crank journals. .010 is taking .005 from each side/.020 is taking .010 off each side/.030 is taking .015 off each side. so between .010 and .030 the margin .010. the crank will be fine.
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Old 08-24-2005, 08:49 PM
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Thats why I came to the pros fror answers
I only have had cranks polished or cut to 10/10 or
traded for virgin crank.
however ,
with the raising cost of gas...............
(when something is to blame,blame it on gas prices)
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