Boring a block brings the cylinders back to new condition, only slightly larger. Oversized
In this installment, we tackle how to prepare the block, how to choose the right cylinder heads, the differences in crankshaft and piston qualities and the procedures required for them, and rod reconditioning. Later on, we'll discuss rings, the quench factor, and engine balancing.
I have read several articles in your magazine on how to rebuild engines. Most of these articles assume the reader is an expert on engines and knows what the writer is talking about. I've also read several books on Mopar engine rebuilding and still can't figure out some of the things the writers are talking about. Since I don't plan to rebuild the engine myself, I really need a detailed list of what I should do to my '70 Barracuda 340 four-barrel engine. I would like to have it rebuilt to stock specs, but I don't know what questions to ask, nor do I know what exactly should be done. To reduce the risk of receiving poor quality work, I'd like to know these things before I take the car in for the rebuild. Your help is greatly appreciated.Lawren MinorVia e-mail
Lawren, rebuilding a 340 to stock specs was covered from top to bottom in the December 2000 through February 2001 issues of Mopar Muscle. We showed how to tear down a greasy junkyard engine, how to inspect it, what parts to get, and what machining was required for a low-dollar but solid buildup to original specs. Then we took it to the dyno, ran it in pure stock form, and bolted on an extra 110 or so horsepower with four aftermarket additions that anyone can do. We can't get any more detailed than that.
Boring brings the block close to the final dimension, while honing finishes up the final s
While it's easy to get caught up in the serious end of the engine world, we realize there are Mopar fans at various levels of experience looking to wrench on their toys. We know some of our tech is pretty hardcore for those new to engine building. Really, it doesn't take long to get up to speed, just starting with the basics and working up. With that in mind, we'll get to "splainin" some of the things to know and think about when digging into an engine for a rebuild.
The block is the foundation of any engine, whether the goal is a stock rebuild or a radical high-performance piece. First on the list of things to consider are the cylinder walls. Cylinder wear tends to be tapered, with the greatest amount of wear at the top of the piston-ring travel and little toward the bottom. The more wear and taper, the more wiggle room the piston has in the bore. As the piston becomes unstable in the bore, sealing against both combustion pressure and oil is compromised. Making matters worse, in a tapered bore, the piston rings move in and out in their grooves, following the taper. The result is accelerated wear in the piston-ring groove and further deterioration of the rings' ability to seal.
Reconditioning the cylinder bores requires a trip to the machine shop to have the block bored out and honed to a larger dimension. Then, corresponding larger pistons and rings must be purchased to match. The engine will gain a couple of cubic inches from the larger bore, but more importantly, the cylinder will be in a perfectly round condition to seal as well or better than new. An overbore, the purchase of new pistons, and having them fitted to the rods is the most expensive part of a basic engine buildup, but for good-as-new performance, it's money well spent.