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Building Your First Engine on a Budget

If you mess around with cars, sooner or later you're going to find yourself in the position of needing to freshen an engine - here's how to do it cheap

Photography by Marko Radielovic

The Drop Off

Once you've picked an engine and established a relationship with a reputable machinist, it's time to deliver the core. You could provide the shop with a complete engine, but disassembling the core will save some expense, and the shop staff will likely appreciate the effort. Besides, if you've done any of the initial checking we recommended in the core selection section, you should have already pulled off the heads and the oil pan at a minimum. The best approach would involve completely dismantling the engine on your own, while keeping and labeling all the old parts. The old camshaft and lifters can go in the dumpster along with the timing chain and gears, but some of the used parts should be retained. For instance, after the pistons are pulled from their bores, make sure to bolt the caps back on and keep the old bearings in place-the machine shop may want to use them for preliminary measurements. The crank should be removed from the block, but handled carefully-the journals are vulnerable when out of the engine, and damaging them is remarkably easy. Wrap the journals in rags or put the crank in a heavy plastic bag until you drop it off. To prevent warping, crankshafts should be stored by standing them on end, not laying them on their side. Once the crank is out, bolt the main caps back in place, again retaining the old bearings and keeping everything in the same position it came from.

When you arrive at the machine shop, you should have a bare block with the main caps fastened, a crank, and the pistons and connecting rods you plan to use, plus the cylinder heads if the originals are to be rebuilt. Don't disassemble the heads-let the machine shop handle that.

When we dropped off the 350 at Dougan's, we'd already disassembled the engine and degreased it. This made it easier for the machinists to give it a quick inspection before we even took it out of the back of our truck. It also saved us the labor cost of having a shop employee toil over a grimy mess. The original bearings were left in place in the mains and the rods (we brought the old piston/rod assemblies just for reference) and the crank was transported on the floor inside the cab to avoid damage from rolling around in the bed.

Plan of Attack

When you turn your parts over for evaluation, you're making a commitment. Some machine shops will do a preliminary check of the cylinder bores and maybe a few crank journals to determine if you're handing over junk, but time is money, so once the stuff goes in the back, you've pretty much incurred expenses. Step one is usually a bath for the block in the hot tank. Most shops will do this before any serious handling of the parts.From here, the parts will be more accurately measured to determine what needs to be replaced or resized. This is why new parts shouldn't be ordered until after the machine shop thoroughly inspects your hardware. For example, you may have measured the bores yourself and determined that perhaps 0.030-overbore pistons are what you need, but if the machinist discovers a groove or other imperfection in one bore that won't "clean up" at 0.030-over, you may actually need to go for the 0.040 pistons. That could mean a costly error in judgment on your part if you already ordered the 0.030-over slugs and rings.

The next step is usually the crack-checking procedure, often referred to as Magna-fluxing-a trade name for the process of magnetizing colored iron powder to reveal cracks or flaws. This process may be considered optional, but it's well worth the expense. You don't want to rebuild a boat anchor. If the block and crank receive a clean bill of health, you're ready to discuss the actual machine work. During the inspection, the machinist will have determined the size of the bores and crank journals, and from there will determine if these dimensions need to be altered, and by how much. Most American V-8 engines require an overbore after significant use because the bores are worn to the point that they are larger than standard and no longer round. The ridge left at the top of each bore where the piston rings reached the top of their travel is often a tell-tale sign of the extent of the wear.

If you're lucky enough to have a block that's been slightly used, you may get away with only a cylinder bore hone, but if there's any significant wear, go for the overbore. The machine shop will likely recommend the minimum oversize, and this is when you'll find out what pistons to order. The crank is more likely to have less visible wear, though it will probably have some scratches. Light grooves can often be polished out, but anything that can catch a fingernail will probably require machining. It's common practice to machine crank journals 0.010-inch under the factory diameter (sometimes 0.020-inch); this simply means you'll have to use the corresponding oversize bearings. Rod and main journals can be resized independently of one another, though all of the journals of one type will generally be taken to the same dimension. For some engines, bearings are available in 0.001-inch under and over sizes, which can be handy for closing up the tolerances on unmodified cranks that are just a hair under standard due to wear, or are just a shade tight after machining.

After inspection, Field agreed that our 350 showed very little wear, but suggested we give it a light hone to clean up the cylinder bores rather than installing the new pistons and rings against the wear patterns of the original stuff. He also suggested we spin-balance the rotating assembly, since our new pistons and rods were significantly different in weight than the originals. Field realized that the budget for a basic project like this should be kept within reason, and worked with us to minimize costs without sacrificing the quality of the job.

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1 comments
452RBchevy_c10
452RBchevy_c10

Not sure why people do not read this first before embarking on a engine project.

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