Chevy 350 overbore?

[slasmith1]

Re: Chevy 350 overbore?

I went through this exact issue two years ago found out the hard way that for marine applications you should never exceed a .020 overbore. the cylinder wall becomes too thin to properly cool and handle the loading that marine use puts on an engine. I had a shop install a rebuilt Chev 350 in my bayliner 2455 first motor lasted less than 4 hours 3100 rpm cooling fine oil pressure fine and just stopped dead. had 1/2 " cracks in two cylinders full of water this was a .040 over bore.
Engine number two lasted 7 hours before i met vessel assist similar to eng 1 but was a .030 over bore.

engine number 3 was a .010 overbore lasted until i sold the boat in Oct still running well it is currently moored two slips down from me has approx 175hrs.

 

[chiefalen]

Re: Chevy 350 overbore?

Not for nothing that motor had other issues.

For example overheated so many times that the bore had nothing to do with the cracks would have had the cracks if never bored over.

Maybe there were hairline cracks and never discovered.

 

[meesh]

Re: Chevy 350 overbore?

That's the exact reason a lot of overbores dont live. Many rebuilders are too cheap to spend the time and money to magnaflux a block. It's all about production. Many cores come in cooked, are torn down bored rebuilt and sent out. Many as the chief pointed out with hairline cracks. And yes since they were'nt checked properly, they will fail.

 

[cantaris]

Re: Chevy 350 overbore?

This engine was bored and magnafluxed.

 

[Bondo]

Re: Chevy 350 overbore?

You can bore a good 350 block with no core shift .125 oversize.

Ayuh,...

I hate starting what may turn into a pizzing match,...
But,....
That quote is Pure Bullzh!t.....

There's No Way a 350 can be bored to 400 spec.s without running into the cooling jacket.....
Period.... Especially a block cast after 1986...

I also Question some of the other statements being posted,...
Standard overbore pistons are only avialable in .030,+ .060 sizes...
I've Never seen a .010 or .020 over bore pistons offered for sale Anywhere....
And,.. there are Few choices for a .040 overbore Piston....

Custom Pistons are not part of this duscussion,...
Because it would drive the Cost of a rebuild to Beyond that of a Brand New motor....
And, .010, .020,+ .050 Are Custom pistons... .040 pistons are pretty Rare...

 

[Fishermark]

Re: Chevy 350 overbore?

I agree with Bondo. EXCEPT... .040 being rare. If by "rare" you mean not common, then okay. But .040 pistons are easy to find and buy and cost no more than any other size. But the .010, .020, and .050 - yep. What he said.

 

[cantaris]

Re: Chevy 350 overbore?

Well at very least the outdrive and trailer and other components will be worth the money. The engine .....well I will just have see the measurement myself prior to rebuild. If I have go with a different block then I can get one easy enough. May I will take it to a machine shop of my choice and get their input.

 

[mthieme]

Re: Chevy 350 overbore?

The only time I've ever heard of .125 over involved sleeves...and it wasn't a SBC. Racing doesn't count.
The overbore could explain the 400 heads though.

 

[chiefalen]

Re: Chevy 350 overbore?

Maybe the first time i had to disagree with Bond-o

Called my friends again they said .040 overbore is quite common, and the pistons etc, are easy to find and cost the same, and theres a guy near me that stocks them.

Maybe it's cause of the raceway, and he's near there, and if he don't have them in stock, one day they will be in his store.

Bye the way this same store,( won't use the name in the forum ), got me in one day, the timing cover for my 120 when i first got the boat.

One other thing i asked them about the .125 and i can't use the language here.
But it involved bovine droppings, and something about a lie---m----r f-----.

Just repeating sorta the guys opinion.

 

[mthieme]

Re: Chevy 350 overbore?

Fortunately I learned just this morning that a bull is a bovine.
The things you learn here. I can see my grandson searching iBoats in another 10 years in lieu of college.

 

[chiefalen]

Re: Chevy 350 overbore?

If you go to the link, then you might think it's my brother-in-law, but the pic in the link is better looking.

http://knowledgerush.com/kr/encyclopedia/Bovine/

 

[mthieme]

Re: Chevy 350 overbore?

LOL. I'll Have to take your word for it about BIL.
Good link. Thanx.

 

[slasmith1]

Re: Chevy 350 overbore?

sorry for the misinformation after reading these posts I went through stacks of paper on the motors I described the first two were .040 both were supposedly magnafluxed. look on ebay and you will find all those hard to find piston sizes they are by no means rare.