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 six..." 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 aso a catastrophic failure. The engine had been fully machined, bored .040-inch over, and was a strong runner. That is, it was, until it went away with a bang and a rush of water into the crankcase blowing steam out the breathers like Old Faithful. A post-mortem evaluation 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. We disassembled the block, and just to have a look, smashed out the broken section of the cylinder wall with a ball-peen hammer. We'd at least have the satisfaction of figuring out just what went wrong. 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, and not as thick. The flaw was in the highly loaded thrust side, and provided a spot for the wall to let go.

We happened to stop in at Precision Speed and Machine, and were jawboning about our bad luck with the doomed small-block, when machinist Dave Massey suggested what seemed obvious to him--why not just sleeve it? Huh? Why not is right.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? That depends. Looking at precedents, sleeves are standard equipment on blown fuel and alcohol race engines; but those are a little different, being 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 actually gain cylinder wall integrity. Oddly, back then sleeved engines were found to produce more power than integral bores blocks. There were no honing plates in those days, and the sleeves isolated the bore distortion from the headbolts.

Now to make it clear that we are not just blowing sunshine, there can be some compromises with sleeves. Foremost, there is the possibility of water leakage past the sleeve and into the crankcase. This can be avoided with proper technique, including using an anaerobic sealant between the liner and the block, along with sufficient press, or interference fit. Another potential pitfall is block distortion, particularly if a healthy press accompanies the sleeve installation. The adjacent cylinder walls are often distorted in the process, so the best solution is to figure on a full re-bore and hone of the block at the time of sleeving. This is usually par for the course if the block is being sleeved in the course of a major rebuild, however, even if the block is being sleeved as a repair on a fresh engine, the adjacent cylinders need to be measured and typically re-honed for roundness. A skilled machinist can work wonders here. Finally, if the original cylinder wall is machined nearly fully away, a portion of the deck's integrity is also lost, in relation to the head bolts' clamping ability.

Our 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 ran around $100 at the time of our repair, with other required machining operations such as honing and decking the block billed at the normal rate. The bottom line is, 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 sleeve wall-thickness is 0.093 and 0.125 inch. 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, though as mentioned, deck strength and cylinder head fastener clamping will be somewhat compromised. The correct machining technique must be used to ensure the appropriate press and purchase at the top and bottom of the block material, with a register at the crankcase side to locate the sleeve.

We took our 318 block to Precision Speed to fix our bruised bore. Dave recommended a 0.125-inch thick wall sleeve to repair our windowed block. The repaired 318 is on our engine stand now, awaiting a rebuild in the 400-plus hp range.