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Join Date: Feb 2005
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Crankshaft cross drill

Hi Guys,
I am about to embark on a monster 3.5 l motor. I know this motor will spin between 7200 & 7700 rpm, based on the cams etc.

I want to cross drill the crankshaft (3.2l 74.4m), but am concerned as to the possibility of weakening the crank.

Is there any reduction in the strength of the crank with the cross drilling, and would the cross drilling need to only go to the oil passage in the crank, or all the way to the other side of the journal.

You advice is appreciated, as I don't want to make a mistake.

By the way, I will be using the GT3 oul pump.

Thanks in advance.

Old 04-14-2007, 12:08 PM
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This cross drilling of 911 crankshafts seems to be a recent development. I could be wrong but I don't think Porsche did this on any of it's race engines including the 800 HP 935 engines. I think this is a solution in search of a problem. So far I haven't heard of any crankshafts breaking due to this mod however.

I don't know for sure but I suspect if you matched the oil holes that are already in the number 1 and number 8 main journals you'd get what you want. I don't have a crankshaft in front of me right now to see if there are 2 holes or 1 in these journals. You also have to groove the main bearing to supply oil to the holes you are drilling.

-Andy
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Old 04-14-2007, 04:37 PM
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Quote:
Originally posted by Eagledriver
This cross drilling of 911 crankshafts seems to be a recent development. I could be wrong but I don't think Porsche did this on any of it's race engines including the 800 HP 935 engines. I think this is a solution in search of a problem. So far I haven't heard of any crankshafts breaking due to this mod however.
-Andy
Hi:

We've been doing this since 1979 as thats the only effective way to ensure sufficient oil to the center of the crank at high RPM.

Porsche didn't do it for a long time and suffered #2 & #5 rod bearing failures,...

Properly done, it doesn't affect the durability of the crank.
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Old 04-14-2007, 10:47 PM
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Agree'd. The center drilling of the crank is a mod well worth doing. Although, I would not rev the engine past 7200 without other mods accompanying the center drilling. I think Steve would agree.
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Old 04-15-2007, 12:00 PM
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Quote:
Originally posted by gtu935
Agree'd. The center drilling of the crank is a mod well worth doing. Although, I would not rev the engine past 7200 without other mods accompanying the center drilling. I think Steve would agree.
Absolutely!!!!
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Old 04-15-2007, 12:26 PM
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Good show Steve. I always enjoy reading your posts. I am sending you a pm
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Old 04-15-2007, 12:32 PM
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I stand corrected. Thanks for the information.

-Andy
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Old 04-15-2007, 02:09 PM
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Pic of a center bearing being grooved



finished bearing


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Old 04-15-2007, 05:12 PM
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