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

[Mike T]

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]

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]

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.