[DeTomaso] 2-bolt versus 4-bolt

[Larry - Ohio Time Corp]

John,

Interesting read. If I have a brain cell left on a Monday. Would it then be
true to say that straight 4,6,8's are better on cap walking as the load is
in the same plane as the bolts?

Larry - Cleveland


-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of John Bentley (jab)
Sent: Friday, October 26, 2007 5:22 PM
To: detomaso at realbig.com
Subject: [DeTomaso] 2-bolt versus 4-bolt

For those interested in engine engineering, I recently had an email
exchange with my Dad (engine designer at Ford) on pros and cons of the 2
and 4-bolt blocks.  Here is what he had to say.....
 
************************
2bolt/4bolt
The V engines produce high main bearing loads due to gas loads at
approx. 45 deg. from the horizontal, and as the RPM increases the high
loads are produced at all angles. Sideways loads to the right cause the
left outboard side of the cap to lift away from the block. When the
bolts are near the bearing bore as in the 390/428, the contact pressure
between the block and cap is quite uneven, which makes lift-off easier.
The higher the side load, the more the lift-off. When the lift-off gets
near the c'bore for the bolt, fretting occurs on the saddle face and a
fatigue crack starts (crack is in fore-aft direction). The crack
progresses up the hole and thread until complete failure occurs. The
extra 2 bolts were introduced to prevent the parallel-o-gramming
lift-off.

However, if the main bearing bolts are located farther outboard towards
the center of the contact pad, the contact pressure is more even and the
lift-off is minimized or prevented.

The 351C and 460 bolts are rather well placed, and that type of bulkhead
failure never occurred (that I know of, in production engines).

There is no functional disadvantage to having 4 bolts, but it provides a
margin of safety not generally needed.

One disadvantage of an aluminum block is that it has no endurance limit
and therefore stressed areas will fail someday.

********************************
 
I guess I read from that you don't have to search the earth for a 4-bolt
block unless you are building a pretty high HP engine.
 
FWIW,
 
JB

 
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