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.
A nasty crack developed up...
A nasty crack developed up the cylinder wall of this 318 block. Figuring it was scrap, we smashed out the broken part of the wall with a ball-peen hammer for a closer look at the fracture. The hole in our 318's bore could have spelled the end for this .040-inch over block. Why scrap it when a sleeve can have it as good as new? We had machinist Dave Massey at Precision Speed and Machine fix it up.
The chunk of cylinder wall...
The chunk of cylinder wall told the story. A section of wall showed the crack propagated from a thin spot, which had eroded to about .060 inch from the backside.
Step one is getting the block...
Step one is getting the block set up exactly square for boring. Dave measures fore and aft along the crank centerline to ensure the bore will be exactly 90 degrees to the crank.
To check the axis across the...
To check the axis across the decks, the decks are swept with an indicator. This technique is accurate if the decks have already been blueprinted square with a JBA fixture, as had been previously done with this block.
Installing a sleeve requires...
Installing a sleeve requires a precisely sized and cleanly machined bore. Dave dressed the carbide cutting tool on a tool grinder to assure a sharp tool for a smooth cut.
A sleeve needs a register...
A sleeve needs a register at the bottom of the bore to serve as a locating ledge to which it will be solidly retained. Rather than going all the way through as in a usual bore job, the machine needs to be set up to stop short of the end of the original bore. This indicator is set to gauge the depth of the cut.
The outside diameter of the...
The outside diameter of the sleeve is measured and the amount of press desired is subtracted to determine the dimension the block will be bored to.
With the large window in this...
With the large window in this block, the actual purchase of the sleeve into the block will primarily be at the top and bottom, since there is no wall in a good portion of the middle. Dave prefers to use a substantial amount of press in cases such as this. The machinist installing the sleeve has to be hip to what's required for sizing after examining the block, to provide the strongest possible repair when the after-machining sleeve thickness and remaining cylinder wall thickness are calculated.
With the setup complete, and...
With the setup complete, and the relevant measurements noted, the boring can begin. The boring operation is done in several steps, until the final cut is made to precise size. Dave kept the depth of cut a few thousandths off the bottom index of the indicator, preferring to give it a final clean-up to the target depth on the last cut.
Dave measures the bore with...
Dave measures the bore with a precision bore gauge after each pass of the boring bar to keep track of the progress. Actual size is recorded and compared to the machine measurements for material removal to ensure there are no discrepancies.
The block isn't bored all...
The block isn't bored all the way through, but a step is left at the bottom of the bore to serve as a register, positively locating the sleeve.
To ease the installation,...
To ease the installation, the liner is chilled in a special apparatus with CO2 gas, causing it to contract.
Installation of the sleeve...
Installation of the sleeve is done with a driving fixture and a big mallet. The sleeve is driven in until it is solidly against the register at the bottom. Sealant is used inside the block and around the sleeve prior to driving it in.
When the sleeve bottoms against...
When the sleeve bottoms against the lower register, it will stop abruptly. The tone or ring of the hammer blows will distinctly change when it is fully seated.
Next, the block returns to...
Next, the block returns to the boring bar, this time to have the excess sleeve material above the decks cut down to within a few thousandths of the deck surface in preparation for surfacing.
Then the cutters are changed...
Then the cutters are changed and the cylinder is bored to size, in this case bored in preparation for final honing to the original .040 inch over dimension.
Our block was carefully measured...
Our block was carefully measured and shimmed so that the surface cut could be held to a minimum, and then machined to bring the top of the new liner dead even with the block surface.
The sleeved hole looks as...
The sleeved hole looks as good as new.
The last operation is to finish...
The last operation is to finish hone the bores. The sleeved cylinder needs to be honed to size, but the adjacent cylinders also need honing to correct for distortion caused by the sleeve's press fit. We had Dave torque plate hone all of the holes while the block was in the machine.