Fitting Billet Main Caps and Line Boring on a CNC Machine Center

Mike T

Well-Known Member
May 3, 2013
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Dave, What is the minimal amount of interference fit that we can get away with and still keep the cap from walking? # 3 on mine can be knocked into the register with the palm of my hand.
 

turbodave231

Moderator
May 24, 2001
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Macomb, MI
www.geocities.com
You need a couple thousandths press. If using a stock cap, they can either be knurled on the register area or carefully center punched to raise the metal. Steel caps can be Tig welded and machined flat.
 

TURBOTIMMER

Active Member
Jan 5, 2002
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Amity, Pa
This is great info. I’m at this point right now on my forged motor. Tore it down finally after 7 years of abuse. Last time I drove it, oil pressure was low, so out it came. Main bearings are beat, one started to delaminate. No 3 cap is no longer tight in the register. This was in a 3600lb (with me in it) limted. Car ran low 10s over the course of the last 5 years and one 9.90 pass in 2015. Mph would be anywhere from 132-137 depending on how much boost. Motor never ever saw more than 2 degrees of knock retard, and it only happened once. I will tell you your crank will still move around even if its steel. I have a forged stock stroke crank, 2 billet caps, and its hard blocked up to the bottom of the coolant ports for the timing cover.
This is great info. I will now have my block magged to make sure there’s no cracking in the main saddles. Its going to the machine shop tomorrow.
 
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