The Stovebolt Site Forums The Shop Area Engine Shop cylinder bore question

ok so im checking bore in my motor befor i get new piston rings and i notice that the upper 1/4"-3/8" of all the cylinders has a lip-not from carbon- its only about 0.02" diffrence, and the pistons still travels all the way up the cylinder to just under the deck. the bore i measured at the top of the cylinder is 4.001" witch is factory bore size, but just a little further into the cylinder (just under the aforementioned lip) the bore gets slightly bigger. is this normal? its a 62-63 327cid. do i need to adjust the piston ring size because of this, or is that the way it is supposed to be for this motor?

i think it's common if the engine has some wear. be sure and check in all directions, they tend to wear more in some ways than others. just in case you didn't know.

if it truly only has 0.002" wear you might get by with a hone. now is the time to do it while it's apart. good luck

Some bore wear is quite normal, did you mean to type 0.02" wear? That's a huge amount of wear in a standard bore. If it's .002" that's no problem, just make sure you either get new rings which have a step in the top ring, or get your machine shop to remove the bore ridge with a ridge reamer. Otherwise you risk breaking the top piston ring against the ridge when the motor is running.

Stuart.

i will have to double check, but i know it is quite noticeable, i thought i remembered the measurement to be .02. it was enough to notice it when i was not looking to see if the wear was bad. ill double check tomorrow.

Most people remove the ridge. You want to check each cylinder in multiple places depth wise and at each location take a bore reading parallel to crank and at a 90 to crank.

Check shop manual for exact locations.

Dan Bentler

Brian, Yes the bore wear measuring .020 OS is typical is typical of a used engine and may be found with 25k mi of rough service or as much as 150k of good care and service.
The rings MUST be sized for the minimum dia cylinder they will RUN IN or they will not fit the cylinder well anywhere in their travel until well worn.I would use chrome rings of original bore size.
As previously stated the ridge should be removed to allow the piston removal without damage (top ring land) and to prevent the new rings being damaged by contact on every upstroke.
Normally bores wear more @ the extreme top of travel and do not wear round and different bores in the same engine will have slightly different amounts of wear--this is really noticible when boring cylinders as the boring cut is concentric with the unworn part of the cyl and some parts of the cyl are "cleaned up" before others.Many the front cyl will wear more than the back-I think because they see the cooler water from water pump and TOO cool running promotes cylinder wear.
With .020 measurable at the extreme you would need .040 overbore to totally clean up the wear.I find these early engines were considerably softer metal than later ones and some other brands.I was raised on stovebolts, have loved and massaged them for 50 years and rebored/repaired many, but I believe that GM screwed the user well by not using the best material as soon as it was available for engine block material.
Many engines with your measured wear are still giving good service.I would guess your main complaint is high oil consumption --please be informed that these early v8's are not normally as thrifty on oil as the inline 6 and I would never worry about mine if it used around 1 quart in 1000 mi--you may not see much better than that after a rebuild unless some other changes are made.
If much blowby is evident the ring replacement will be necessary but if only plug fouling is the complaint a easier cure may be in line.
These early engines flooded the top end w?oil and the valve seals were insufficient to prevent oil being drawn down into the inlet (high vacuum) and even the exhaust.The cure is like the later engines had after approx 1982.A good stem seal like the Perfect Circle VS2.But the heads before about 1964 must have a simple machining job to the upper guide to allow the seal installation(requires head removal and teardown).Later the factory machined the guides but wouldn't spend a few $ more for the seals so only if the dealer or mechanic had wanted to put them on after owner complaints was this a common cure.
A v8 chevy head repair must have these seals installed in my estimation to assure the best oil control.
Many shops knurled the guides internally to restore valve/guide fit but this not a good cure for oil control without the seals.
I have used the seals successfully without removing the heads if the guides are already machined.And the guide/valve fit is not critical for a head REPAIR, Not rebuild.
A good indicator of oil control by the rings can be found on the piston tops before cleanup--If the edges of the piston top appears washed clean and free from carbon it is from oil being wiped up from below and cooling the comb process but if a fairly uniform carbon coating exists the rings are still doing a good job.
These engines are so tough they don't have to be perfect to do a good job but there is a satisfaction that comes from putting one back like near new--it's just that there are so many places to put the money if we listen to every voice.
Have fun.

Cylinder wear more than .005" (5/1000 inch) is too much to do a re-ring job. The rings have to expand and contract every time they move from top to bottom, and the ring loses its tension rapidly. At 2,000 RPM the ring is changing diameter 67 times PER SECOND! Rebore the cylinders and install new oversize pistons in the straightened-out bore. A re-ring in a bore with .020" taper won't last over 5,000 miles, and the engine will use oil from day one!
Jerry

Ever bore one with a torque plate on it and could that play a bigger role than temperature?

Curt, Never bored one after a torque plate(that I know of) or with a torque plate but most were the first rebore.Just was stating that there is a easily(without measuring)visable difference from 1 cyl to another in the accumulated wear.When successive cuts are made a trend in patterns of greatest wear are visable.In a number of flathead 6 industrial I once did the pattern revealed more wear on line with rotation and most times more on 1 side than the other in line with the pin and a little more in front cyls than rear.The ability of piston rings to seal and conform to changing cyl shapes is wonderful and I can assure you .005 taper or .010 is a very acceptable amount if the piston ring lands are not loose or deformed.It would be great to have bores always in perfect shape but the only time they are thus is unused or after very low use.From the time you start up they start to take on the shape that will move away from round and true.How many times have you had the head off an acceptably performing engine for reason other than rebuild and been horrified to find scary cylinder conditions but been able to reassemble and get farther usable life.
But enough excuses not to do a complete rebuild.If it were mine with .020 measurable wear and known ring or bottom end problems I would go through it completely but it's hard to judge for someone else how they should spend their money.
A man needs to know when and where to compromise.

I like to do simple ring & valve jobs & put an engine back in service for awhile, but I can't imagine useing .020. cyl wear. I thought he was talking about .002.