Resurfacing deck, affect on cylinder bores

I noticed the odd bank on my 340 block has a .012" taper from front to back (checked by moving (1) piston/rod assembly to each hole and measuring the piston height.) The block has been bored and honed with torque plates, if I resurface the deck to square up with there be any significant affect on the cylinder bore? I'm thinking maybe a little due to the slight change in angle of the pull of the head bolts but enought to really matter; I doubt it. Any opinions?

Wow .012 is a lot :shock: I would double check your piston to deck height numbers by checking the deck flatness end to end with a straight edge and feeler gauge. Generally they use a hardened and ground straight edge calibrated to be flat within .0002 per running foot.

It's flat, just tapered from end to end. Don't know what kind of precision to expect out of automotive machine shops (in our shop we work to tolerances of .00008") so I don't know if I can take it to someone to square up or if I have to figure a way to mount the block in our mill so I can do it myself. :scratch:

I take it that it was progressive, for example: .000, .004, .008, .012 difference front to rear and the same rod/piston combo showed no taper on the opposite bank.
As far as an engine block geometric tolerancing, the deck parallelism is called off the crank centerline, not the rod journals which are eccentric.
Both banks would need to be decked and the intake manifold milled as well. Whether decking a block or milling heads, I think the formula was .0095 off the intake per .010 removed from the headgasket surface for a LA engine.

Take it to someone with a BLOCK TRUE Fixture

Typical Chevy shop shlocky workmanship, I be choking the living $hit out of the fool that did that work

That kind of work is done by an old school miller. The block is positionned and leveled using a machinist's bubble level and an eyeball. Have a shop using up-to-date machines do it. (my shop uses a Rottler F-65) They should be able to get at least within .0005" of perfect..An added bonus is, the finish is much better for the gasket, and the deck is squared to the crank centerline...Good machining does wonders for horsepower and torque. :afro:

I'm not going to mention who did the work because I really think my block machining does not really represent the work they normally do. I will say that they are a major Moper shop with alot of satisfied racers out there. I will be traveling in the area of the shop next month and will stop by and talk to them about this.

I'm working with a guy in Sycamore, IL now and he is pretty good. He setup his machine square to under .001", mounted the block and checked it and realy found some odd numbers. Each bank on the block is tapered the same but in totally opposite directions?? Not only that but the odd side is quite abit higher than the even. The only thing we can figure is that the block was indicated using the factory machine work and just cleaned :scratch: Got a little concerned that maybe the line hone was bad but it checked out ok. I'll be picking up the block tomorrow and will post the final results.

I agree with you on the benefits of good and accurate machine work, we work to tolerances under .0001" at work and I'm very picky. I'm just glad I checked my block out and didn't assume. Lesson learned!

The opposite sides are high most likely because the block was truned around on the miller. The trick is not to get it "flat" per se, but to get it flat and parallel to the crank centerline. Some fixtures dont do that, some do. I'm not trying to knock anyone, just pointing it out. The factory machining is terrible anyway. :afro: did anyone else notice you cant see my afro with the dark background??

Visited te machinist yesterday and he was able to confirm my findings: approx .008" taper across each bank but in totally opposite directions. Also confirmed the difference in height in each bank, between cylinder 1 and 2: .018" :shock: Fortunately the height of the "odd" bank is actually +.010 over blueprint spec so I should end up around .010" under blueprint; should be ok.

Update:

Got the block back from the machine shop, max variation between the four corners is about .001": :cheers: My calculated deck height is now 9.585". I measured the quench height on all the pistons and now know how much I have to mill off them to work with the closed chamber heads. As soon as that is done I can CC one of the pistons and see where my resultant CR is. Due to the deck milling I should not have to touch the heads but I wont know for sure until the pistons are done.