Max overbore

[CaptRon66]

I found a possible replacement for my cracked block. It is for a Mercruiser 165 straight 6. The machinist tells me he would have to sleeve cylinder 1 and bore the others to .040. Is this ok? I think Mercruiser calls for .030 max. What problems could this cause? It is raw water cooled engine in an old boat. I don't see owning this for more than 5 years. Could the thinner walls cause the cylinders to crack? or cause an overheat in the cylinder?

 

[picklenjim]

Re: Max overbore

I would think .040" over would be no problem at all.That's basically a chevy engine which I'm sure they bore to at least .060" over.Your only talking .005" difference in the wall thickness between .030" over and .040" over.My BB chevy is bored .100" over and can still go to .125"..040" over you are only cutting .020 off the wall.Shouldn't affect your cooling any either.

 

[Bondo]

Re: Max overbore

Myself, no way would I put that kind of work into an old block when its so easy to find a decent one.

Ayuh,... A Standard Overbore is .030,... Most Chevy's will take .060...
But,... The Sleeving is the Deal Breaker in my book,... That ain't cheap...
And,...
These Aren't at all Uncommon blocks... There's BaZillions of them...
Many 250cid Pickup truck blocks have the Needed front mounting Ear...

 

[maxxman04]

Re: Max overbore

yeah, what Bond-o said. seriously.

 

[CaptRon66]

Re: Max overbore

$200.00 to sleeve the cylinder. Yep that is expensive. I must not be looking in the right places. It took me a long time to find this block. Junk yards don't have them near me. It's getting to the point where I may just buy a rebuilt engine. Time consuming looking for a rebuildable block.

 

[gadget73]

Re: Max overbore

Ideally, you'll want to have the walls sonic checked to be sure they can do that kind of overbore. Most castings will take it, but nasty cooling systems and raw water cooling will seriously degrade how much overbore you can safely handle. Get those walls too thin and the cylinders will distort, and thats definitely not a good thing. The sleeve is also a bit worrisome. Its a 250, you should be able to find a good donor from a junkyard truck or something. Check yards in Pennsylvania if possible, many of them seem to have a lot of older stuff. I know of at least 2 that are almost guaranteed to have several. Also might want to check car-part.com, its a junkyard search engine that might be of some use for you.