Yesterday I finally did a more close up look at the cylinder bore and I can feel a wear “ridge” on all the cylinder walls. The “ridge” is just below the engine’s block about 0240” below the piston TDC. See attached picture. The “ridge” is on all cylinder. What can you tell me about what potentially has caused this, I know that re-boring the block will remove this ridge and potentially new rings and piston are required. This engine is already 0.030” over size.
Blowby will cause wear. And what you describe is normal for these 70 year old engines. If it were mine, I would hone the cylinders with a stone hone. Back when I thought I had to have Snap On tools, I paid big bucks for a hone, but they can be bought pretty cheap these days.
Compression and combustion pressure is highest in the first inch of the piston travel at the top of the cylinder. That pressure gets behind the top piston ring and pushes it tight against the cylinder wall. That pressure, even more than the tension of the ring itself, is what seals the ring against the cylinder wall and keeps hot gases from blowing past the rings. It also promotes wear. At 2000 RPM, those rings reach the top of the cylinder 120 times a second. The cylinder wears tapered, with the maximum wear happening in the first inch from the top.
Here's a quick way to measure cylinder taper wear: Remove one of the rings from a piston, and square it up snug against the ring ridge. Stack up several feeler gauge blades to measure the ring gap. Record the measurement. Use a piston to push the ring to the bottom of its travel and measure the gap again. It will be noticeably smaller because there will be little or no wear near the bottom. Subtract the lower measurement from the upper, and divide by 3.14 (Pi). The result will be cylinder taper in thousandths of an inch. For example: Upper gap: .040" Lower gap: .025" Difference: .015" .015/3.14 = .0047". That's right on the ragged edge of too much wear- - - - -doing a re-ring job on a cylinder with over .005" of taper wear will result in very short ring life- - - - -the ring must flex too much to maintain contact with the cylinder.
Reboring the cylinders and installing oversize pistons and rings eliminates the taper. Most stovebolt engines can handle overbore sizes of .060" or even .080". Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
My engine stand should arrive by the 14th. Then I’ll be able to further assess the cylinder vs piston. Being that I’ve highly considered a local engine shop do honening and if required to bore the cylinders.
If the wear is within limits for a re-ring job, also get them to put a knurl on the piston skirts to take up the extra clearance created by the honing job. It's "old school" technology, but it works. Honing a few thousandths away to eliminate taper wear also creates a sloppy piston fit and causes noisy engine operation. Putting a knurl on the piston skirts gets the clearance back within limits, and also traps oil for better piston lubrication. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Look on Ebay for a cylinder ridge reamer, prices are all over the place but you will get an idea of what they look like. It's a tool used to cut the ridge off the top of the cylinder if you do not bore the cylinders. The rings wear the cylinder but they also get a slight radius on the them that matches the radius on the now formed ridge. It's possible that new rings can hit this radius and break them, so it's best to cut the ridge off for smooth cylinder. They cut easy with a decent tool, I still have the one my dad used 50 years ago and it still cuts pretty good. Once the ridge is removed, you can hone the cylinders.
When you get ready to clean the block for assembly, ask around and see if you can find a scrubbing pad off a floor buffer. The janitors at work know me and give me the old ones that are about worn out. I cut circles just bigger than the bores and stack them on a threaded rod, usually 3 or 4 circles. Then tighten down the nuts to hold them from spinning and chuck up the rod in a drill. With the block standing on end, I spray lots of Simple-Green as I am running the scrubbier in and out of the bores. I keep going till the foam is white and all the imbedded grit is removed. Work from top down till all cylinders are cleaned, then rise with hot water. Dry it best you can and have a wad of paper towels and WD40 to wipe out the flash rust with. The scrubber pads really shine up the walls and just remove the micro edges left from the hones. These are what I cut up. LINK
Joe
Last edited by klhansen; 09/09/20266:19 PM. Reason: Cleaned up link
I was taught to always remove a ridge whenever pistons are going to be removed. I've seen fellows try to knock pistons out the top side and break rings...even saw a man once wedge a tiny piece of broken ring, keep trying and mess up an otherwise okay piston. If you can't find a reamer down your way, let me know. If you want to pay postage both ways I'll loan you mine. You may be able to find one on eBay for what the postage would cost, however. And a machine shop might loan or rent you one. Good luck.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
Spring-loaded "glaze breakers" are not sufficient to actually hone the taper out of a cylinder. They simply follow the wear pattern and shine up the cylinder surface without doing anything to correct the taper wear. To correct cylinder taper during a rebuild, a rigid hone such as this one is needed, followed by knurling the piston skirts to correct the clearance back to specifications.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
JonG, good info. My plan is place it on the engine stand flip it over and after removing oil pump and whatever else is in the way I would remove the piston/rod assembly from the bottom. Then remove the crankshaft for visual inspection, followed by removal of the camshaft.
Jerry I never knew of knurling piston skirts. I’ll see if the shop that I’ll have the block reworked at has performed that mod.
after removing oil pump and whatever else is in the way I would remove the piston/rod assembly from the bottom. Then remove the crankshaft for visual inspection
The "whatever else" will be the crankshaft. Pistons won't come out the bottom with the crank installed.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
Most, if not all of the pistons won't clear the main bearing webs. There are only a few engines I can think of that the pistons come out the bottom- - - -like the Cadillac flathead V8 used before 1949- - - - -the connecting rod big ends are too big to pass through the cylinder bore.
Whatever else you do, the ring ridge MUST be reamed away before new piston rings are installed. The top ring land will break when the new rings hit the ridge otherwise.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
