Me and my dad just pulled an old 1976 1/2 ton 4wd chevy pickup 2 bolt engine. Thing is this thing is pretty rusty, intake, heads, cylinders! The motor is stuck dang it. I think its the rust obviously. The cylinder has raised rust in 1 of em. But heres my real question. I read on at least two of the pistons, 030. We're told that it probably wasn't overhauled. I'm thinking that it was bored to .030 tho. Then we spoke to another guy with a 400 and he said they came with 030 stamped in em. Were they stamped like that as std? If so i wonder if 060 is enough and how much that damages a daily driver block. Thanks for any help. later --jarrod.

I don't think I've ever seen anything with .030 on it other than a .030 over piston. I think the guy that said that standard pistons have .030 over on 'em is mistaken.

Check a crank bearing. If it's a GM bearing it might be a stock engine but I'd guess you'll find Clevites or something. As above - I'd guess it's bored out.

The factory pistons did not have that. It is the oversize diminsion,, originally 4.125 the block has been bored for 4.155" pistons.
Question is why is there rust in that cylinder. Cracked head, or cracked block? Don't spend a nickle on it till you find out for sure,, AND, I sure wouldn't even wast the $ to have the block checked. +.030 is OK, +.040 if you MUST, but +.060 on a 400 block is a shakey deal. If all the bores are good but the one, have it sleeved, these 400 castings are getting pretty hard to find. But there is a point of diminishing returns. It's easy to dump $1000 in an old broken casting just to get it to the point of usable.

The factory pistons did not have that. It is the oversize diminsion,, originally 4.125 the block has been bored for 4.155" pistons.
Question is why is there rust in that cylinder. Cracked head, or cracked block? Don't spend a nickle on it till you find out for sure,, AND, I sure wouldn't even wast the $ to have the block checked. +.030 is OK, +.040 if you MUST, but +.060 on a 400 block is a shakey deal. If all the bores are good but the one, have it sleeved, these 400 castings are getting pretty hard to find. But there is a point of diminishing returns. It's easy to dump $1000 in an old broken casting just to get it to the point of usable.


What he said ^.

The factory pistons did not have that. It is the oversize diminsion,, originally 4.125 the block has been bored for 4.155" pistons.
Question is why is there rust in that cylinder. Cracked head, or cracked block? Don't spend a nickle on it till you find out for sure,, AND, I sure wouldn't even wast the $ to have the block checked. +.030 is OK, +.040 if you MUST, but +.060 on a 400 block is a shakey deal. If all the bores are good but the one, have it sleeved, these 400 castings are getting pretty hard to find. But there is a point of diminishing returns. It's easy to dump $1000 in an old broken casting just to get it to the point of usable.

good point and if it's already at .030 over good chance the rust won't clean up at .040". I looked for a 400 sb and just gave up. The ones I found were cracked or the owner wanted too much for the block and one guy made it clear that the block was as is.

Thanks all and especially Marv, that was a very good answer. The pistons have the 030 and we used a digital meter to find it was around 1.150 which is a .030 bore pretty much and you can see engraved matching numbers underneath when they overhauled it. We only have the one side open right now because two of the exhaust manifold bolts wont budge. GRINDER TIME. Ya that amount of rust im sure that a 040 won't do it. I was wondering what people thought on a .060 but it sounds like it's a bad idea. So is a sleeve real spendy or what is the deal on them? Again thanks for the help.

I forgot but the machine shop said I needed a few sleeves on a bb I had and it was cheaper to just get a different block.
.060" over can be done but have the block sonic checked. Some blocks are pretty thin at .030" so it's hard to say. I still wish gm would sell the big sb blocks at the price of the 350 block. Sell them like hotcakes and put fear in those other brands. lol

I had a sleeve put in my old 400 block and had nothing but problems with it, head gaskets and the head studs started pulling where the sleeve was. I talked to a couple of machine shops later and they said they would never sleeve a 400 or bore 60 over, 40 max. Welcome aboard and good luck with the car.

My local shop won't sleeve a 400, either. There's not enough bite to get 'em to stay anchored and it's a crap shoot as to whether the sleeve will work or not.
Keep looking, IMHO

The thin spots on the 400 blocks are where the cylinders are scalloped to clear the head bolt holes. Of the 400 blocks that I have sonic tested, most were over .200 thick at .030" over on the thrust surfaces, but would still be thin where the head bolt holes are. We will sleeve a 400 block for a mild engine or to salvage a race engine with lots of money into it, but the factory iron between the sleeve and the head bolts gets very thin and it's common for the head bolt holes to crack after the fact.
Don't start a project with a rusty, already used up block, you'll be throwing good money after bad.....find another 400 block with a virgin bore that will clean at .030", buy an aftermarket 400 block and have a bulletproof foundation for ANYTHING you want to build down the road, or just build a 383 using a good 350 block. Good luck!