Looking for more advice...

just a question to ask your opinion!

i was deglazing my cylinders to see how they clean up. There is a score mark in 1 hole, I can barely catch a fingernail on it. Would I be wasting time and money building it with out boring it out?

Looks pretty nasty in the picture……

You might get away with it …but I'd bore it to be safe.

mike

What do all the bores measure for size and taper? That might answer your question.......................

Hope I say this correct...

they measure very close to the 4 inch bore, so they have not been bored out yet.

they vary 2 to 3 ten thousandths out.

With all respect unless they are brand new it's doubtful they are only worn .0002 to .0003 in size and taper. Two to three thousandths (.002 - .003 ) would be more reasonable. Were it me if the bores are all truly only a couple of thousands out, and the engine will be only lightly used I would be very tempted to use the bad bore as is. An option would be to re-bore and sleeve the bad bore back to 4". Cost would be minimal........................Bob

If you are going to reuse the original pistons, check those too. If they are damaged or worn out of specs, that will influence your decision. You might try honing out the scratches using a coarse stone and then finish with finer stone appropriate for the rings you will use. The service manual (55) says you can use the original bores if wear is less than 0.006" (I ran one for 25K that had up to 0.014" wear --- it was noisy, but probably would still be running if there wasn't a cam failure). I would not be afraid to use it. Too many of us rebuild these engines to run 300,000 miles and will never do 10% of that. Use the best moly rings and don't buy from a vintage supplier...that is the same ring set that Ford, Chrysler and other GM used on engines with a 4" bore(ie chevy 350).

Willie

I would be concerned about HOW that scratch got there, as it's all the way from top to bottom, plus some lighter ones in other locations in the bore. What does the piston skirt look like?

In many engines, at least in the 1970-80 time frame, GM had some "high-limit" pistons sized at about .008"+, which might explain why the '55 service manual lists using the stock size piston at up to .006". Same with crank bearings.

Question might be just how deep is that scratch? But the REAL issue would be where to find a piston! In the world of small block Chevrolets, if a bore has any wear on it, it usually takes a .030" overbore just to get the cylinder "cleaned up" and to "fresh metal" . . . at a minimum . . . which is pretty common, from what I've seen. IF the bore will clean up at that overbore size, then a .030"+ piston might be procurred (OEM, if possible . . . which we've been over before in these NailHead rebuild threads). ONLY thing is to exactly match the weight of the existing stock piston and pin combination with the weight of the new piston and pin (aftermarket pistons seldom are the same weight as OEM pistons, especially the overbore sizes, which GM matched all the way to .030"+, usually). This way, the existing "balance" will be maintained and you only need to do one cylinder . . . which might be less expensive than a sleeve.

As for Old-Tank's observation on rebuilds, I somewhat concur, except that it might not cost that much more to use OEM-100Kmile spec parts (especially if you can get them at the "rebuilder" price rather than the "consumer" price) than to use something else. By the same token, a block with great machine work and OEM-level parts should easily go 300K (provided you use an upgraded timing chain) with reasonable care and modern synthetic motor oils. Sometimes, it doesn't cost that much more to go "first class", with the KEY thing being to ensure you get what you paid for, in the first place.

Enjoy!

NTX5467

I would fully inspect the ring groove langs on the suspect piston as well. If they are radius out of spec then when you reinstall the new set of rings on the old piston you will have a leaker and if the grooves are badly out of spec the new rings could break as well. Also we realize this has been discussed in length on other posts, but don't run today's standard spec oils as the ZDDP mg+ & p protection is no longer there nor a sole synthetic oil alone in a flat cam old engine as the synthetic will phase out of solution sooner if not later. Either way you will get premature cam and lifter wear in either case.

As mentioned, if the "ring land grooves" are worn, usually vertically, the rings will NOT be held squarely against the cylinder bore as they move up and down with the piston. New piston time, if that's the case. If the lands do not have square transitions from the groove to the side of the piston, you might need a machine shop's opinion on the issue.

Just some thoughts,

NTX5467

Just following up... The block went to the machine shop, crank ground and polished to .010 and the cylinder walls needed to go out to 40 over. It's getting the full treatment, new pistons, cam lifters.

quick note, most of the cylinders were all worn equally, the score line went away at about .020 but the #2 & #3 cylinders had additional wear, which is why it ended up at 40 over

Just thinking … but along with that 40 over job you can also put on thicker head gaskets then spec to lower the compression for today's fuels while your at.

Just thinking … but along with that 40 over job you can also put on thicker head gaskets then spec to lower the compression for today's fuels while your at.

No, use the 0.015 (thin) head gaskets since all replacement pistons are a compromise and lower compression than the original. Also, for all its' bad qualities ethanol in gas raises the octane. All of my 55's that previously required premium or midgrade run fine on regular 87 octane except in hot weather when the cylinder head temperature is up.

Willie

Good Points Willie ! - Then come summer is the time to sneak blend in that leaded airport 100 octane non percolating fuel :cool:

I thank you all for all the input...but I truly value the input!

but just know, I have a source for 93 octane, non-oxygenated fuel which costs a little more but contains zero ethonal. I use it in all my toys, the Buicks, bike, mowers and trimmers...

…. Good thing that no methanol source you have. Can't get it straight up good stuff at all out here on the right coast but can buy it when I was in the Mid West this past winter. Guess they know even if they make the crap-o-la ethanol there that no one in their right mind would put ethanol in a car that will sit for more than a week so they also offer real unleaded at the pumps as well.