Low-Buck 302 En­gine Build


Mustang Monthly - - CONTENTS -

How to tell what you’re work­ing with and be­hind the scenes in a ma­chine shop

THERE ARE COUNT­LESS REA­SONS FOR RE­BUILD­ING AN EN­GINE, AND COUNT­LESS MORE DI­REC­TIONS TO TAKE THE BUILD ONCE YOU’VE STARTED, BUT FOR US THE REA­SON­ING WAS SIM­PLE. In short, our lit­tle small-block 302 was wellused and needed a re­fresh. While we were at it, we de­cided we might as well spend a few ex­tra bucks ( but not a bunch!) and squeeze a lit­tle more per­for­mance out of it.

It all started with a routine oil change on our largely stock 1971 en­gine (the only real modifications to the 302 in­cluded an Edel­brock Per­former 289 in­take man­i­fold, an HEI dis­trib­u­tor, and an old four-bar­rel Carter AFB car­bu­re­tor). Ev­ery­thing was fine and dandy un­til we no­ticed the oil had an un­usual shim­mer to it—dang. Luck­ily the en­gine had been run­ning fine and we hadn’t no­ticed any­thing out of the or­di­nary be­fore this, so the metal­lic sand-like flakes we were see­ing most likely just meant one or more of the bear­ings were wear­ing out. Out came the en­gine, and after a quick tear­down we found even big­ger metal chunks in the oil pan and oil pump pickup. It didn’t take long be­fore we found the cul­prit: the No. 1 cam bear­ing was half gone. Ev­ery­thing else looked in­tact with no other vis­ual dam­age, so we de­cided to go ahead with the re­build.

The plan was to re­use as much of the block, ro­tat­ing assem­bly, and var­i­ous other parts as we could so we could spend money where it would count. We were think­ing a set of low-buck alu­minum heads, a cam, lifters, rocker arms, an alu­minum in­take man­i­fold, and a car­bu­re­tor would do the trick, but we’ll get more into parts se­lec­tion in Part 2 of this tech story. For now, it’s off to the ma­chine

shop where we will show you how to check clear­ances to de­ter­mine what can be sal­vaged and what needs to be tossed. Then we’ll walk you through each step of re­fresh­ing a long-block from bor­ing and hon­ing all the way to bal­anc­ing the ro­tat­ing assem­bly and ev­ery­thing in be­tween.

The ma­chine shop we’re work­ing with on this build is Hollins Auto Ma­chine Co. in Or­ange, Cal­i­for­nia. John Hollins, owner and long­time ma­chin­ist, has been in the business for over 50 years. In fact, he has op­er­ated Hollins Auto Ma­chine Co. out of the same build­ing for 52 years now, so he knows a thing or two when it comes to breath­ing life into an old en­gine. We fol­lowed John through the whole ma­chin­ing process to hope­fully give you a com­pre­hen­sive look at ev­ery­thing that goes into an en­gine re­build. You’ll soon get an idea of what you can do at home and what you’d rather let a pro han­dle. For ex­am­ple, get a good set of mi­crom­e­ters and you can do most of the de­tec­tive work your­self, while stuff like cut­ting the deck and re­con­di­tion­ing the rods are bet­ter left to a real ma­chin­ist.

If you’re em­bark­ing on your first en­gine re­build, or just want some good tips and tricks for your next one, fol­low along as we take a worn-out old 302 long-block and get it ready for its new life as a wal­let­friendly driver that per­forms.

Our story be­gan with a dis­as­sem­bled bare block, along with the stock crank­shaft, rods, and pis­tons, which we dropped off at the ma­chine shop. To get things started, John hot-tanked the block to get it clean for ma­chin­ing and then mag­nafluxed it to check for cracks.

With ev­ery­thing look­ing good he moved on to check­ing cylin­der wear us­ing a dial bore gauge. First, he mea­sured at the very top of the bore and found it to be the stock 4.000 inches. Then, he mea­sured just un­der­neath the ridge on all cylin­ders and found 0.010 inch to 0.020 inch of wear, which meant we had room for a 0.030-inch over­bore.

Next, John used an out­side di­am­e­ter (od) mi­crom­e­ter to check rod jour­nal and main jour­nal wear on the stock crank­shaft. Based on the stock di­am­e­ters, he found that the rod jour­nals would need a 0.020-inch grind and the mains would need a 0.010-inch grind (we will keep this in mind when it comes time to buy new bear­ings). The crank was then sent out to be turned to those spec­i­fi­ca­tions.

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