The Stovebolt Site Forums The Shop Area Engine Shop GMC 270 Cracked Cylinder - Advice Please

Hello All,

Am looking to put together a spare 270 for my '44 CCKW. The current engine runs great, but with 80 year old iron, I have found that is always good to have a plan B.

Anyway, I purchased a complete engine and trans from a '56 250. I was originally targeting this for my rebuild project, but included in the deal was a second, parts engine, that was totally disassembled. These parts look reasonably unmolested. Crank and cylinder bores are nominal, so it has probably not been rebuilt.

I started looking these parts over with an eye on rebuilding it instead of the complete engine. However, while inspecting the block, there is considerable pitting on the deck surface. I'm thinking it will need at least a 0.020" shave to clean it up. Even worse, on cylinder # 2, I noticed a crack that starts approximately an inch from the deck, and extends about 2" down the bore. I'm thinking the block saw some frozen water in a cooling jacket at some point in its past?

Assuming there are no other cracks or defects, what is the typical success rate of installing a sleeve in that cylinder? I'm assuming the crack would at least have to be mitigated by drilling a hole in each end prior to the sleeve installation. Or is there another preferred method?

Just trying to get a feel if this is worth fixing, or if I should just pass it on to the scrap man and go back to my original plan.

Any thoughts or input would be greatly appreciated.

Best Regards...

I don't see why that couldn't be sleeved, but folks who know more than me, will chime in, I'm sure :-) If there are no other cracks, I'd say sleeve it and rebuild.

Start by honing the cylinders a little to eliminate the rust, and inspect all of them with a bright light and a good magnifying glass for other possible cracks. If you don't find any, sleeve that cylinder. Stop-drilling the ends of the crack is probably a good idea, but it's not absolutely necessary. Use a thin sleeve- - - -3/32" wall thickness. That minimizes the amount of material you'll need to remove to install the sleeve. There are also 1/8" wall sleeves available, but those are usually used to repair cylinders with holes in them, not cracks. Leave a small step (about1/8") at the bottom of the cylinder for the repair sleeve to bottom out against- - - - -that traps the sleeve between the block and the cylinder head so it can't move after it's pressed into the block.
Jerry

Thanks, Jerry.

That's just the type of advice I was looking for.

Bob

One detail I forgot to mention. If the crack does not extend to either the top or bottom of the cylinder, a sleeve repair is possible. A crack that's all the way to the crankcase can allow a coolant leak into the oil because pressing or driving the sleeve into the cylinder can open up the crack and cause a leak behind the bottom of the sleeve. Ditto for the top- - - -compression and/or combustion chamber gas can bypass the sleeve at the top and get into the cooling system. The rule of thumb I've always used is there needs to be at least 1/2" of good metal at both the top and bottom of a crack.
Jerry

Thx, Again.

One thing I've always wondered about.. When they install a sleeve, is there any sealer or loctite type adhesive used ? Or, does the sleeve just rely on the interference fit ?

When I had SS sleeves installed in my wheel cylinders, I seem to recall them using red loctite as they were pressed into place.

I usually bore for a .0015-.002 press fit and use a BFH and a heavy steel plate to drive the sleeves in. No sealer. The shock of hammering the sleeve in seems to make for a better fit than trying to install sleeves with a press. Once the sleeve reaches the lip at the bottom, it should protrude a few thousandths out of the top of the block. Then I use a big file to scuff the sleeve level with the block surface. If you're milling the block to remove surface pits, install the sleeve first.
Jerry

Not always, but quite often we use liquid nitrogen to install sleeves when repairing industrial equipment. The liquid nitrogen will shrink the sleeve .004-.005 and it just slides right in. We also usually shoot for a .0015-.002 press fit.

But,I’ve never sleeved an engine block before. So I’m not sure if the extreme cold will affect the grain structure of a cylinder sleeve. However, It does work real well for our applications.

John

Over the years, I have installed hundreds of bushings using liquid nitrogen without encountering any issues related to the cast iron being adversely affected.

From my observations, the thin sleeve of the bushing does not have sufficient mass to transfer enough cold into the cast iron casing (block in this case) to cause any damage or structural changes.

The block wasn’t my concern, I was mostly wondering if the extreme cold (-320 F) would alter the integrity of the cast iron sleeve.

I know very little about Metallurgy.

John

We used to install huge bronze bushings, like 12 inches in diameter by six inches long, into tire curing presses by immersing them into a vat of dry ice and alcohol for an hour or so. They would shrink enough to be an easy slip fit.
Jerry

I had salvage liners installed 60 to 70 years ago and it was a cheap but lasting fix. It is still a reliable fix, but I would expect it to be expensive. And before you go machining the deck and installing a salvage liner, it would be wise to have the cylinders sonic tested. After 80 years the block may have rusted from the inside. There is a guy near here https://www.eatonbalancing.com/ that does that. He is big into Y-Blocks, but he would test a GMC also. I would look around for a better block. If you are just looking to build a spare you have plenty of time.

I used to buy competitors' "worn out" racing engine blocks (mostly 350 Chevy) that had been bored .060" and run until there was a little taper wear in the cylinders, for pennies on the dollar- - - -sometimes free for the taking. "Zero-gap" piston rings had a nasty habit of wearing the cylinders barrel-shaped, with most of the worn area halfway down the stroke. I was teaching high school students engine machining at the time. I'd buy 8 thinwall sleeves and use those blocks as student projects. I ended up with a standard bore race-prepared block to build up for the racing team I was working with. The kids learned good machining practices. Win-win, except for the guys who couldn't figure out that they were getting beat on the race track with their own junk!
Jerry

When using thin-wall dry sleeves one should consider not hammering them very hard even with a piece of wood across the bore. Better to shrink them.

I have installed dry sleeves in engines that were sleeved from the factory. Most had a flange at the top to trap the sleeve between the block and head. I removed them by running a bead of weld up the sleeve in a couple of places to shrink them and tapping them out with a long brass drift. There are sleeve extractor tools for pulling them and wet sleeves too. Too expensive for a one-time job though.

To install I packed them in dry ice from a nearby caterer for an hour and knocked them in with a hard rubber mallet. I have seen instruction for repair sleeves that included a countebore for a flanged sleeve. Don't know if that's common in light-duty applications.

Anyways, the further you get into such a project, the more expensive mistakes become and installing the sleeve is the last operation.