Chevy 350 overbore?

[cantaris]

Hi all. After alot of the "That Merc165hp is under powered for that 24ft fiberglass boat. Get a 350", I came across a chevy 350 tthat has a new(never seen water)block that has been bored .040 with the plates? installed. The original block got cracked after a previous rebuild. It has 400 low compression heads??? New marinegasket set, rings, etc. The engine is in pieces and need s reassembly. Block just got bored and Magnafluxed and new ca bearings installed by a machine shop. The person I am buying it from is in the military and is getting transfered. The engine comes with a 19ft Bayliner runabout with anice trailer( which I will get rid of). Is this going to be a descent engine for $500?
http://seattle.craigslist.org/oly/boa/995647306.html

 

[Bondo]

Re: Chevy 350 overbore?

Ayuh,....

A Standard overbore is .030,... Donno Why they went .040....
Pistons might be hard to find...

The Chevy 400cid Heads are Crap,...Toss'em,+ get a set of Vortecs...

It appears that you're supposed to gut the Frozen motor,+ reuse the internals for the New motor,...
That concerns me, in that Most Machine Shops won't even start to cut a block, til the internals are On the bench,+ can be Measured...

If you have use for the Drive parts, the Trailer,+ maybe something from the Hull,...
$500. might be alright...
But,..
If All you want is the Motor,.... I'd Pass....

 

[Don S]

Re: Chevy 350 overbore?

You are going to find that it takes a lot more to change from an IL6 to a V8 unless you use drive and all from that boat.
Your present setup does not have an exhaust Y pipe for a V8, and hard to say if you can put one on the transom shield you have. If you get past that, then you have to get Merc exhaust manifolds, and risers and Y pipe, hoses elbows etc. NOT cheap unless you can find used. But you would wnat to use new manifolds and risers anyway.
Then you may have to make stringers for the side motor mounts for the V engines.
One possibility is to use the Volvo drive and transom shield and exhaust setup that is on the doner boat.
Personally, I would take a 280 Volvo outdrive without trim ahead of any pre Alpha outdrive any day of the week.
The 1.65 gear ratio in the Merc drive will have to be changed to a 1.50 also.
As you can see, it's just NOT an easy changeover.

 

[cantaris]

Re: Chevy 350 overbore?

Sorry I wasn't clear. When I talked to the guy, he said the old cracked block had been tore down by the machine shop. And the new block was in the process of going back together but he is being transfered. So he is going to pick up all of the parts today so I can get them tomorrow. As far as changing the L6 to the V8, I was thinking of pulling the Volvo penta stuff off of the Bayliner and putting it on boat. The merc setup would then be sold or put in the Bayliner and sold. He told me that the cracked engine had just been rebuilt but was no winterized properly by the previous owner. Accorrding to him the machine shop said everything was still good. He did buy new ring set gasket set cam bearings, etc.

 

[mthieme]

Re: Chevy 350 overbore?

I don't think .040 is a show stopper or any of the other motor parts.
I do agree with Don, this is only a part of it. You might find yourself needing everything else behind the motor. You might consider starting to look for a donor.

 

[chiefalen]

Re: Chevy 350 overbore?

How much meat is still left in the cylinder walls after the oversize .040 bore.

Besides that you say it's ready to go back together, with all the pistons and everything for 500 bucks and the boat and trailer.

The donor boat has the setup to drop the motor into ?

Than whats to stop you from putting the motor together, pulling everything out of the 24 footer and dropping everything into the 24 footer from the donor boat ?

The volvo drive is geared correctly ?

Hell much better a volvo outdrive, sell whats left over from the 24 footer you might make a few extra bucks on the deal.

 

[Fishermark]

Re: Chevy 350 overbore?

block that has been bored .040 with the plates? installed.

The "plate installed" part of the ad simply means it was honed with deck plates installed during the honing process. It mimics having the heads bolted on for a truer hone.

If you're worried about whether or not 40 is too much over - I would check with the machine shop which did the boring. They have a tool to measure the actual thickness of the walls. Due to shifting in the casting process it is too simplistic to say that a given overbore is too much. Sometimes 30 is too much - other times you can go quite a bit beyond that. Bottom line, I would check with the machine shop if it were me.

 

[Don S]

Re: Chevy 350 overbore?

Merc, Volvo, and former OMC, all recommended the max bore be not more than .030 over standard size. They didn't even sell rings or pistons over .030 oversize.
Having said that, all (or at least 90%) of the aftermarket engine rebuild houses, never even measure the bores, they just automatically go to .060 oversize for everything. Saves time, how else can they make money on them. That's one of the reasons I really don't like those type engines.

 

[Fishermark]

Re: Chevy 350 overbore?

Don - the difference in this case, if I understand correctly, is that this block work was done by a local machine shop - not a mass produced rebuild factory. I'm with you and the rebuilts you can buy from various vendors. I have seen all kinds of mis-matched parts, etc in those engines.

 

[Bondo]

Re: Chevy 350 overbore?

I don't think .040 is a show stopper or any of the other motor parts.

Ayuh,....

With your clarification,...

You're buying an Assembled Long Block for $500.00,..??..??

A .040 isn't the end of the world,... .060 is Usually the Max for a SBC...

 

[Don S]

Re: Chevy 350 overbore?

Don - the difference in this case, if I understand correctly, is that this block work was done by a local machine shop - not a mass produced rebuild factory.

I understand that, what I was trying to get across is the fact that .030 is max recommended by the manufacturers, but .060 oversize is also used with sucess. His .040 is just over max "SUGGESTED" by only .010.

 

[chiefalen]

Re: Chevy 350 overbore?

This intrigued me so much i called a couple of guys i know that are experts.

They build and race at Englishtown raceway.

They just told me over the phone what Don S posted in his last 2 posts.

He was just quicker typing.

No problem with the overbore, one guy even has a monster Cig. boat with 2 monster motors. He also said no problem.

 

[meesh]

Re: Chevy 350 overbore?

.040 over wont hurt a thing. We used to run .060 at the track all day long with no problems. Even have run plenty of them on the street but you can get into overheating issues if you overbore. For a daily use boat I would'nt run over .040. Get yourself some 350 heads. You can use the 400's but you will have to drill out the steam passages to make them work. In a 400 block the center cylinders are siamesed and they dont have coolant flow between the like the other small blocks do so you would have to modify those heads to use them and it's not worth it.Besides they dont flow that well anyway and like it was pointed out earlier you'll be way ahead with a set of 350 heads.

 

[chiefalen]

Re: Chevy 350 overbore?

I'm interested in exploring why there were 400 heads on the old motor?

It's all ready to be put together, machined the heads must have worked before.

The heads gave more power what was it rated at ?

This machine shop does marine motors ? Is what i am really asking.

 

[Bondo]

Re: Chevy 350 overbore?

I'm interested in exploring why there were 400 heads on the old motor?

Ayuh,... Probably because they were sitting on somebody's shelf....

Without a Casting #, it's an unknown as to whether they may offer a hpower increase, or decrease....

Generally speaking,.... Being a 400 Head, only means the steam holes have been drilled in them,....
Nothing more, nor Less....

 

[meesh]

Re: Chevy 350 overbore?

Simply stating he's safe at .040

 

[chiefalen]

Re: Chevy 350 overbore?

All things being equal if it is only .040 i don't see and my 2 experts don't see a problem.

One guy with the boat asked a question, what kind of oil pump is in the new motor?

Racing motor on the track and a marine engines are 2 different dogs.

 

[cantaris]

Re: Chevy 350 overbore?

Thanks for the replys. Unfortunately I called and told the guy I would have to back out because of the first few posts saying how much work was involved. I got scared about the .040 bore. I wouldv'e had to drive 200 miles round trip and then I was going to have assemble all of the parts. As far as the 400 heads go he said they came off of the original engine. I would have changed everything over to my boat and then sale my merc setup. So I take it volvo is better? than a merc?? As far as putting a V8 in place of my L6 I didnto think that would be much of a prob as I have to replace all of my stringers, frames and transom. But OH WELL!. I will keep my eye out for another deal hopefully one that is fresh water cooled.

 

[cantaris]

Re: Chevy 350 overbore?

Well the opportunity re presented itself and I am picking up this boat and engine. So I will be posting questions concerning changing out the outdrive to the volvo penta 280.

 

[Faztbullet]

Re: Chevy 350 overbore?

You can bore a good 350 block with no core shift .125 oversize. Ran em in jet boats for years with no problem. Here is link to Mercury Reman Site and their reman process:

Welcome to Mercury Remanufacturing
The parts?
Many parts used by local engine re-builders just don?t hold up to the demands of a marine engine. Mercury Remanufacturing uses only marine-proven parts in our engines. Teflon-coated, high-silicon pistons, stainless valves, premium-grade bearings and rings, marine-grade gaskets and all-new head, rod and main bolts are just some of the lengths we?ll go to give you a durable end product.

The process?
We thoroughly inspect all cores. All of our blocks are disassembled, sonic-cleaned or oven-baked to remove debris, hot pressure-washed and reinspected ? any damaged parts are scrapped ? never welded or repaired. Each block is bored to a max .040 over (max .030 or re-sleeved on outboards), the deck is honed and the crank mains are line-honed. Cylinder heads are machined for flatness. Valve guides are machined to accept oversized stems and crankshafts are ground and polished to a max .020 undersize. All connecting rod pin and bearing bores are honed

http://sites.mercurymarine.com/portal/page?_pageid=33,31133&_dad=portal&_schema=PORTAL