TRYME

OK THIS IS ENGINE BUILDER'S 4TH TIME REBUILDING THIS ENGINE. ENGINE KEEPS TEARING UP ROD BEARINGS. NOW HE WANTS TO TURN STEEL CRANK .040 NOT SURE THIS IS OK, ANY THOUGHTS? 454 MAG ENGINE 4 BOLT MAINS
IN THE NEXT DAY OR SO I WILL ADD PICKS OF SOME OF BEARINGS. I SURE WISH I WENT WITH A BOAT ENGINE BUILDER. THERE WAS WATER IN NO. 1 CYLINDER WHEN I TORE IT APART NO DAMAGE TO PISTON OR ROD JUST SPUN ROD BEARING. I HAD BLOCK PRESSURE CHECKED HEADS AND MANIFOLDS CHECK NO CRACKS IN ANYTHING.
WHAT IS ODDS THAT INTAKE WATER JACKET HAS CRACK IN IT?

Crazyhorse

I would strongly recommend that you have the crank magnafluxed to check for cracks. If you were my customer i would insist on it. I would do a .040-under crank for myself (and I have) but I would NEVER do it in a customer's engine.
Pick your stuff up and take it to someone else.

Vinny P

4 times rebuilding the same engine is enough of a reason to go somewhere else.

Hot Boat

If he is using Michigan / clevite77 bearings make sure there is a H marked on the out side of the bearing. If there is a P marked in the bearing then you have passenger bearings and not high performance bearings. There is a difference.

What is done to the motor. Is it stock ???

A lot of time water in the cylinder can be from reversion of a leak in the exhaust manifold

Big Block Billy

What you can get away with in a car motor, you can't in a boat motor. It works too hard. You need to deal with someone who really understands the motor as applied to a boat. I would not recommend going to .040 on the rod bearings, maybe the rods arent right either. Get them resized and maybe arp bolts too. Pm me if you would like, I've been through way too much of this stuff to see it repeated over and over, and watching others suffer... BBB

SB

iTrader: (1)

Root cause needs to be found - it looks like it hasn't.

Is rod bearing damage from detonation possibly ? Or clearances/installation/etc ?

Was this a stock rebuild or have there been other parts changed like pistons/cyl heads/ cam / etc,etc ?

Say a motor comes in broke, the engine get's rebuilt fine, and then it goes out but breaks again with the root cause being a carb that is way out of whack but the engine goes in, get's rebuilt again and the same carb goes back on. I see stuff like this happen a lot and wonder how some rebuilding companies make any money because of the rebuilds/replacements they do under warranty or pressure all over something like leaking manifolds, bad carb, ignition, fuel suplly, or etc/etc that is out of their hands.

Anyway - just bringing this stuff up for some thought. I, of course, have no idea what's being done on your case.

Good luck, and no, I wouldn't feel too comfortable at .040" over.

Crazyhorse

I've used "P" copper-lead bearings in marine applications with great success, even in 500+horsepower engines. I prefer to use them with cast cranks as they are a little more forgiving than the super-duty alloy "H" bearings. That being said, I would also recommend the "H" bearings in this customer's engine.
One other thing about grinding a forged crank-unless it is nitrided after grinding it is actually softer and more prone to cracking than a cast crank.

eliminatethis

on a car eng. i will go .010 - .020 on a hp boat i will not turn it at all the most i will do is polish it the crank is only hardned so deep cranks and rods are to cheep to buy new also all my eng get line bore checked

Big Block Billy

.020 should be the max on the rods and .020 mains on a forged crank in a boat, anything else is potluck even these numbers can bring trouble with alot of HP... .040 is a little crazy... If these were acceptable the crank would have originally have been machined under to save materials etc...
Not the case...
I've thrown many cranks away because they were marginal and not worth magnafluxing or spending anything on them because they were on their last leg so to speak...BBB
Why piss money away on poop !

P Offshore

Run !!!