Low-Buck 302 Engine Build
HOW TO TELL WHAT YOU’RE WORKING WITH—BEHIND THE SCENES IN A MACHINE SHOP
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.