Gen6 cylinder bore question max bore?
 

I have stock GM GEn6 blocks, had engine issues and I am fixing them after tossing a rod, cylinders are pretty rough and I am looking at the possibility of doing a 4.560 bore, is that acceptable on a stock gm block and yes I would have my machinist sonic test, I read lots of opinions on this, I would love solid input..



Thanks..

I'm far from an expert but have always heard max .090" over bore on a stock block.
Beyond that you need a large bore block or the walls are to thin.
Don't take this to the bank and deposit it 'cause it could be way wrong.
Good luck on your situation, I've seen your thread and am heartbroken about those engines.
Poor craftsmanship is my biggest fear as I go to build a new pair of powerplants for my girl.
As youngsters in the mid 70's we assembled blocks in auto mechanics in our junior and senior years of high school with smash out plastigauge for measuring clearances.
As I near 60 I sometimes I wonder if I'd be better served assembling myself in the same manner after machine work.

See ya,
Kelly

4.600 is vary common on the gen 6 block..the only thing that worries me is the stroker crank which is hard on the side walls..yes def sonic test after boaring..if your as hard as you say you are you might want to spend the coin on some dart big m blocks..they are a lot stronger then the gm blocks and dont flex as much under power..

True, looking to see if it's worth using them if it's really not a good idea then I will have to buy blocks, my machinist says that as long as they test ok then there should not be an issue, I am just trying to educate myself more and make sure I don't put myself in another situation....

You would be light years ahead with a Dart block. The thing I don't like about the stock block is the oil system. Seems like you start tearing up parts when you add horsepower and rpm's doesn't surprise me that you lost a rod. That's usually the story with a stock block. If you are a smart shopper a Dart block can be had in the 18-1900 range. Kind of a no brainer with all things considered.

I never heard about oiling issues, not saying there isn't but my buddy's stock block 509's make 800 ho and spin 5900 for years with zero issues, most of the oiling issues I see are assembler error or bad clearancing... Just my opinion

Yes I would love to have better blocks at the same time I am going in for a hip replacement that's going to put me out of work for a while, I can get blocks for 1800 each hard to find that extra 3600 right now that's why I ask if mine are acceptable to use.

Wish I had endless funds lol

I beleive the bow tie blocks have thicker webbing in the mains and also in the piston walls, should be less money if you can find a couple used one's, what's your current bore size ??, if they will clean up at 4.500 leave the other .006 for possibly another rebuild. JMO

What bore are they now?? A sonic test will tell alot

You may be able to clean them up .010 and get custom pistons. Guess it depends how bad shape the bores are in.

Even though these blocks may have only seen freshwater, they may have corrosion issues to consider. Heck, some of the Gen 6 stuff can be 15+ years old by now.

Oh no doubt the Merlin or dart blocks are better.

Bores now are 4.530 that's why I ask if it can go 4.560 if needed ...

they will be sonic tested no matter what I would never take a chance without, the blocks were supposed to be new when done in 06, but you know the story on that clown so who knows, thought about only going .010 more with custom pistons also trying to keep it simple but who knows, noting for me ever goes as planned lol