The truth about engine rebuilds is fairly simple: you get what you pay for. The best thing you can do with your vintage Corvette engine is to take it to a qualified, reputable engine rebuilder with plenty of experience working on Corvette engines. The good news is that any general-purpose engine rebuilder worthy of the name probably works on GM small blocks and big blocks more than any other brand. These engines are the go-to powerplants of hot rods, muscle cars, and race cars all over the world.
When you are looking for an engine rebuilder in your town, consider these factors:
- The best shops don't give approximate estimates, they can say exactly what it will cost to rebuild your engine before you sign the work order. This assumes that your engine block is in satisfactory rebuildable condition, but a reputable shop should know the price on a standard GM V8 engine.
- The first thing the shop will do is write up a work order and make a detailed list of everything on your engine, right down to the nuts, bolts, and washers. That's how you know you'll get everything back. Take a look around - does the place look organized? That will tell you a lot.
- Next, the rebuilder will disassemble and clean your engine. That process can take half the time of the whole rebuild, because engines are usually quite dirty and often rusty. The shop will use a variety of techniques, including baking the parts and using a caustic solvent to remove the dirt, oil, paint and rust.
- Make sure your rebuilder uses a magnafluxing process to identify any cracks in your engine parts - including the block, heads, crank, rods, cam, and so on. The crank should also be checked to make sure it's still straight - especially with high-power engines, cranks can bend over time!
- Also make sure that bolt hole thread repair is part of the stated process in the rebuild. Especially on engines where many bolts may be rusted into place.
- A quality engine rebuilder should always use standard machine shop work. They should align-bore the crankshaft passage and bearing surfaces to make sure that the crank sits straight and doesn't bind. The shop should bore the cylinder walls and decide which size pistons to use after the bores are completely clean and smooth.
- New pistons should always be measured, and the block re-honed to fit the pistons before assembly. Pistons and connecting rods should be machined to identical weight plus or minus half a gram.
- A good shop will regrind the crank and select new bearings based on the post-grind measurement of the crank journals. The connecting rods are also reconditioned and resized in a quality rebuild - with new wrist pins installed.
- Both heads should receive all new valves, valve seats, and new bronze valve guides. Then when the head is assembled, the valve seats should be cut to match the new valves and assembled with new valve springs and shimmed for proper spring pressure. If the engine was originally made before 1974, make sure the engine shop replaces the valve seats with hardened materials to accommodate modern unleaded fuel!
- The crankshaft, flywheel, and harmonic balancer should be spin-balanced before being installed, and then the entire short block should be spin-tested to make sure everything is in place properly. Most Chevy small blocks up to 400 cubic inches are "internally balanced" or "neutral balanced" - those terms mean the same thing. This means they have no counterweights on the harmonic balancer or the flywheel. Over 400 cubic inches, the engine may require counterweights on the harmonic balancer and the flywheel to be perfectly balanced.
- Finally, your engine should be assembled to long block form - which is to say, complete from the oil pan up to the valve covers, but without the intake manifold or carburetor, distributor, spark plugs, or plug wires installed. Also, the water pump, power steering pump, and alternator will not typically be installed on a long block. The addition of all these items is called "dressing out" the engine. Your finished long block should be painted in the correct color (for vintage Corvettes, that's typically blue or orange), and adequately masked to prevent overspray.
This is just a laundry list of things to look for and think about when you're shopping for an engine rebuilder. Be sure to ask your local Corvette club or other GM enthusiasts about the best place to have your engine rebuilt. They will know who's good in your area.