Sleeve Bore Engine Blocks - Sleeve It Save It

We're not sure why, but most people tend to shy away when talk turns to block sleeves. The rap may go, "Yeah, it runs strong, but there's a sleeve in number 6," and somehow it seems tainted. Is there really anything to be ashamed of? We had a warm little 318 that suffered what could have been viewed as a catastrophic failure. The engine had been fully machined, bored .040-inch over, and was a strong runner until it went away with a bang and a rush of water into the crankcase blowing steam out the breathers like old faithful. A postmortem triage revealed the worst-the cylinder wall of the number four cylinder was split like a fat hickory log that lost an argument with an axe. Was it time to walk away and heave it onto the scrap pile? We figured it was, and chipped out the broken section of the cylinder wall with a ball-peen hammer to get a closer look at the damaged area. Though the cylinder wall generally showed plenty of meat, the source of the problem was readily apparent-a thin spot in the wall about the size of a nickel was not as thick. The flaw was in the highly loaded thrust side and provided a spot for the wall to let go.

We stopped in at Precision Speed and Machine and were jawboning about our bad luck with the doomed small-block, when machinist Dave Massey suggested the obvious: why not just sleeve it?

Bore sleeves are nothing new and are factory issue on many H/D diesel and industrial engines. Sure, that may be fine for my tractor, but what about for high-performance use? Looking at precedents, sleeves are standard equipment on blown fuel and alcohol race engines, but those are a little different. That application consists of floating sleeves in aluminum blocks. In a form more closely related, it was common in the early days of blown nitro racing to sleeve 392 Chrysler blocks to strengthen them. Some guys would even use Ford tractor sleeves in 392s, calling these Hemis "Econovans" because they couldn't afford Donovans. Smokey Yunick, in his book Power Secrets, talks about sleeving for strength in NASCAR applications back in the day, again to gain cylinder wall integrity. Oddly, back then sleeved engines were found to produce more power than integral bore blocks. There were no honing plates in those days, and the sleeves isolated the bore distortion from the headbolts.

Our contemplated sleeve job wasn't for strength, but rather for repair. Does it make economic sense? We found the prices quoted locally for sleeve installation varied widely. At Precision Speed, sleeve installation runs $78, with other required machining operations, such as honing and decking the block, billed at the normal rate. What's your block worth to you? Whether a repair sleeve will make for a sound block depends on the installation technique, and what you have to work with in the first place. The most common wall thickness for sleeves are .093- and .125-inch thick. The machinist should select a sleeve wall thickness and diameter that best balances the remaining cylinder wall thickness, if that's a factor in the repair, and the after-machining thickness of the sleeve itself. Even boring all the way through the original cylinder wall and using a thick-walled sleeve will still provide a functional engine, but the correct technique must be used to ensure the appropriate press and purchase at the top and bottom of the block material.

In the case of our 318 block that we took to Precision Speed to fix, Dave recommended a .125-inch-thick wall sleeve to repair our windowed block.