Go Four-Bolt

Sum­mit Rac­ing Equip­ment Shows You How to Con­vert From a Two- to Four-Bolt Main

Street Rodder - - Contents - By Jim Smart Pho­tog­ra­phy by the Au­thor & Cour­tesy of Sum­mit Rac­ing Equip­ment

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.

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