The 1st key to building a reliable engine is having a stable and reliable valvetrain. Spend the time(and money) to research/buy high quality valvetrain products and have someone reputable with marine experience set everything up.

to quote an article we did for engine builder magazine
..."there are no adequate preassembled heads for the marine environment. You MUST buy a bare casting and do your own setup...."

.....

Thanks everyone who asked about piston clearance. I thought I would take a look and now I am pissed at the original builder. He knew these engines were for a boat. He installed KB hypereutectic pistons and the card clearly states for N/A Marine the the piston to wall clearance should be .0035 - .0050 for what looks like a 4.100" bore and up. Mine are .002 - .0025.
https://cimg0.ibsrv.net/gimg/www.off...93c4ceedda.jpg
Might as well get all of this out there. The ring end gap for the 1st ring on my build sheet is: .021 the 2nd ring: .022 and the oil ring is: .025
So now comes the question, Would you go back to this builder, with the new information, and demand that he make it right on HIS dime? He absolutely didn't follow the recommendations from the piston company. I suppose I would / should pay to the have the valve guides done but this has just turned into a complete redo short of parts of course. The obvious problem is that would he do the job correctly or be pissed and not?

No, I would find a reputable marine builder to take them down and start over. I also question why, since you went overbore and had to replace the pistons, the decision to go with hypereutectic over forged. I went forged on my otherwise stock 496 MAG after it bent a rod due to hydro-locking a cylinder. Cheap insurance to help out in case you run into detonation for whatever reason.

So to reach my goal of 500hp using the parts I bought, boring the cylinders was not required and because the bores were in good shape I was able to maintain the standard bore so just a hone. The guy said at my level, forged pistons weren't required. Forged are apparently also heavier(?) and again, just not necessary at my hp level. That was the story.

So, how about them Bears ?
(if your not old, sorry, it’s an old saying)

PQ290,

Just an opinion... There is no such thing as "too strong". I would opt for forged ANYTHING over cast. Just sayin'.....

Thanks. Brad.
(937)545-8991

hypereutectic pistons...? All due respect, you need a new engine builder. That's fine in a stock marine small block and a very stock big block. 500hp? Nah. Car stuff man. Boats are in 4th gear going up hill all day. No shifting, no coasting.

SB, LOL!!!! I am old and How bout those Lions!!!!