The Stovebolt Site Forums The Shop Area Engine Shop Need info to rebuild chevy 250 Inline 6?

Am I corect that a .030 over size piston is 3.9050 Dia. ?
And a .040 over size pistion is 3.9150 Dia. ?
My largest cyl-Bore Dia. measured from the top edge down the cyl. .250" is 3.9096.
Most other cyl's are around 3.9088
So would I use a .040 over size pistion?
Or can I get by with a .030 over size?
The block has not gone to Machine shop yet for re-Bore & Hone job.
All so my CRANK mic's out on the Mains at 2.2985.
And on the crank pin it mic's out at 1.9994
So would I use .001 over size bearings?
Or STANDARD?

From what I can see, you're looking at having to go to the .040s, the smallest cylinder is already past the .030 over size. You probably should wait on getting pistons, rings, and the bearing kit until the machine shop has a look over the block and crank. I learned the hard way. Ordered the pistons based on the measuremnts I took myself, but didn't account for what would actually need to be bored to make it true. Same goes for the crank. You're at the lower end of the spec, the crank may only need polishing, which would men std. bearings. But if it needs turned for truing, best would be to let the machine shop check it first for runout and determine how much needs to be taken off, then get the bearings.

IF the cylinder wear is concentric, you can probably get away with a 40 over piston, but since the block seems to have been bored 30 already, that's cutting a cleanup cut awfully close. How much taper wear is in the cylinder? If the cylinder isn't tapered more than .005" from top to bottom, it might be possible to hone the cylinders and re-ring with 30 over rings without reboring. If there's 30 thousandths of wear in a standard cylinder, ignore the above advice!

Rod and main bearings are available in STD., .001", and .002" undersizes. If the crank is round, and the journals don't taper from one end to the other, it's possible to use the small undersizes without regrinding. Just don't get below reccomended oil clearances. The trick is finding one that's not worn egg-shaped or tapered. Measure each journal in at least six places. Good luck!
Jerry

Only at one spot on cyl. No.6 at the top is it 3.9096. Then its 3.8088 And other cyl's are average 3.9088 at the top of cyl.
If I measure 2" down from the top Max cyl. Bore is 3.8948 only on one of the cyl's And YES cyl bore tapers down to 3.8750 to 3.8760.
This engine had Standard pistons in it.
The crank Mic out at 2.2985 No taper & No out of round. Just 2.2985 no mater where you mic on the Main journal. Same go's for the Rod journal 1.9994. Ok I check it again and only one location on the main journal was at 2.2987.
And YES cyl Bore has alot of Taper. But not much out of round.

The Block is a 230 cid. The crank came out of a 250 cid. Pistons where Standard out of the 230 cid block. The 250 cid block has a taper of .0005 out of round .0005 Bore 3.8780.
The Crank,Cam,Piston Rods im using in this 230 block. All came from the 250 cid block.
Why replace Blocks? On the Carb side of 250 cid block is a foot long crack in the water jacket. Soo I need a new block. Best block I found or got my hands on is this Chevy 230 cid Inline 6 block. Hope this explains it all.