short block rebuild questions questions questions

[edgewood bronco]

I had my block prepared to rebuild, but had a series of events that has me questioning the work. I took it to a second builder to check the work, and here's what he found:
It's a 200 with a 0.030 overbore. Hastings cast iron rings and sealed power dished aluminum cast pistons.

One question I have is how round should I expect these bores to be?
The bores measure as follows (front to back x side to side):
1) 0.0315 x 0.032 over
2) 0.032 x 0.032
3) 0.031 x 0.0315
4) 0.0305 x 0.032
5) 0.031 x 0.032
6) 0.031 x 0.032
I'm not sure from where it was measured in the bore, but i see bore gauge marks up and down the entire cylinder.
I took him one piston, and it measured 0.0295 over.

Another question: There barely seems to be any crosshatch on the bore. The second guy I took it to says there's not enough material left to put a coarser pattern in it. The original machinist says that there shouldn't be a coarse pattern in it, that coarse pattern is old technology and causes rings to wear and engines to smoke prematurely. Should 'be like glass' were his words this morning...EDIT: they use a Sunnen Hone. I'm not sure if that refers to a specific grit or just a brand.

My ring end gap was 0.025, which started this whole fiasco, and i've now got a set of rings for a 0.040 overbore on order so I can at least get them gapped to about 0.015. Do I just gap the rings and go with it, or do I buy a new set of 0.040 pistons and have it redone by the guy who measured the block and thinks the cylinder bores should be round?

I'm not sure how anal I should be getting here. I'm beyond ready to be putting this thing back together, but only want to do it once!
Thanks for your help.

 

[CNC-Dude]

Sunnen refers to the brand of the honing machine and very high quality. However, simply owning a machine like this doesn't make the operator a machinist. You should ask him what grit stones he finish honed your cylinders with. Anything in the 525-625 grit range is normal for cast rings and street rebuilds. The bore clearances could be a little more closer than what you are measuring. You show a range of .001" to .0025" based on the piston size you posted, which shows more than a 50% deviation from one cylinder to the next.

Putting a set of .040" over rings in a .030" bore may get your ring gap in check, but the larger radius of the .040" ring diameter will not allow the ring to make full contact and seat around the entire bore. It may only touch the bore in about 2 or 3 places around the OD, leaving big gaps without any contact at all and preventing ring seating. O/S rings for file fitting are usually only about .005" or less larger than the actual bore.

 

[edgewood bronco]

So is it better to go with my 0.030 over rings and live with the bigger gap?

 

[CNC-Dude]

I would be more concerned with the wide range of bore sizes more then the slightly big gap you have.

 

[bubba22349]

I had my block prepared to rebuild, but had a series of events that has me questioning the work. I took it to a second builder to check the work, and here's what he found:
It's a 200 with a 0.030 overbore. Hastings cast iron rings and sealed power dished aluminum cast pistons.

One question I have is how round should I expect these bores to be?
The bores measure as follows (front to back x side to side):
1) 0.0315 x 0.032 over
2) 0.032 x 0.032
3) 0.031 x 0.0315
4) 0.0305 x 0.032
5) 0.031 x 0.032
6) 0.031 x 0.032
I'm not sure from where it was measured in the bore, but i see bore gauge marks up and down the entire cylinder.
I took him one piston, and it measured 0.0295 over.

Another question: There barely seems to be any crosshatch on the bore. The second guy I took it to says there's not enough material left to put a coarser pattern in it. The original machinist says that there shouldn't be a coarse pattern in it, that coarse pattern is old technology and causes rings to wear and engines to smoke prematurely. Should 'be like glass' were his words this morning...EDIT: they use a Sunnen Hone. I'm not sure if that refers to a specific grit or just a brand.

My ring end gap was 0.025, which started this whole fiasco, and i've now got a set of rings for a 0.040 overbore on order so I can at least get them gapped to about 0.015. Do I just gap the rings and go with it, or do I buy a new set of 0.040 pistons and have it redone by the guy who measured the block and thinks the cylinder bores should be round?

I'm not sure how anal I should be getting here. I'm beyond ready to be putting this thing back together, but only want to do it once!
Thanks for your help.

Do you know what the second builder used to measure the bores? Snap gauge or dial bore gauge? Is it a fresh bored block? If it is I don't see how a boring bar could give those type of results.

 

[edgewood bronco]

my guess is a dial bore gauge. I see opposing 'scrapes' down the bore. Not sure what a snap gauge is.
I never asked though. Never thought to, like so many other things in this process.