Summit Racing Equipment Shows You How to Convert From a Two- to Four-Bolt Main
Summit Racing Equipment Shows You How to
Convert From a Two- to Four-Bolt Main
There’s a lot to be said for the raw strength of two-bolt main journals in Ford, GM, and Chrysler V-8 engines. These engines can withstand incredible amounts of power with two-bolt main caps. However, when horsepower and torque numbers begin to soar to the heavens you need a form of life insurance that will keep your engine together at wide-open throttle at high rpm.
JGM Performance Engineering performs a vast number of four-bolt main conversions annually. Although you can do this conversion yourself it is strongly suggested you consult with a qualified machine shop that can get it done with the great
precision this conversion requires.
In order to perform a four-bolt main conversion you must have a block that lends itself to a four-bolt main conversion along with the availability of four-bolt main caps from the aftermarket. Summit Racing Equipment stocks four-bolt main conversion kits from Milodon, which offers four-bolt main caps and hardware for popular American V-8 engines from Ford, Chrysler, Chevrolet, Oldsmobile, and Pontiac. You may also order a Milodon windage tray and pan from Summit while you’re at it, along with a stud girdle package, which delivers the strength of a skirted block without the weight penalty.
Milodon four-bolt main bearing caps from Summit not only strengthen factory two-bolt main blocks, they can also build in strength with four-bolt main blocks because they’re solid steel billet versus the cast iron these blocks were originally equipped with. These four-bolt main caps are made of precision-machined high-strength steel, which employs the right balance of strength and flexibility.
What makes these four-bolt main caps super strong and solid are the side bolts, which support the main body
of each main cap. These side bolts are angled so that they pull from the sidewalls of the block instead of the main web region. They’ll also load the cap against the register step along the side rails of the block, which prevents cap walk. Cap walk is the undoing of so many engines at high rpm.
Milodon stresses though mild steel main caps may look like main caps and are affordable, they are not always the right material for a performance application. True ductile iron caps take a
beating and return to their original shape, saving your engine’s main bearings and continue to perform well. Very rigid mild steel caps act differently and do not absorb the impact very well. Milodon stresses having flexibility in a main cap.
Milodon adds ductile iron caps also machine better during the line honing phase. They heat and expand at the same rate the block material does so the crank line bore stays round instead of going out of shape. This is why you don’t buy cheap main caps.
■ Although these are not Milodon main caps, they’re a good example of what you can expect from the aftermarket. JGM is going to install them on a fully prepared Ford 460 block.
■ Begin your four-bolt main conversion with a complete set of ARP fasteners (bolts or studs), which will provide solid integrity for your conversion. Main studs provide the greatest security.
Based on this Ford casting number, we’re working with a '70-vintage 429/460 block with two-bolt mains.
■ ARP main studs are screwed into the main saddles to serve as a guide for four-bolt main caps. These studs should not be bottomed out, but instead be screwed in with some room left at the bottom.
■ This is a typical 429/460 bellhousing bolt pattern, which is also common to the 400 Cleveland and 351M block. Four-bolt main conversion kits are also available for these engines.
■ Before the four-bolt main conversion can even begin all main saddle bolt holes are chased to ensure clean thread engagement.
■ With the four-bolt main cap seated as shown, this serves as a guide to drill the side bolt holes. JGM has set this block up on a mill where it can be properly angled for the drilling process. They need drill only as deep as the bolt will reach.
■ The billet main caps straddle the studs as shown, with side bolts being threaded into the webs and rails. Prussian Blue is applied to the webs and lines scribed into the blue to indicate where we need to cut the register.
■ Jim Grubbs sets up the block on the mill as shown to make sure everything is square for milling the side registers where the caps will index.