Sorry to see that you are having problems too, as you know I am looking at two complete rebuilds. This year has been an absolute Bi#ch, I wish you good luck & hope next year is better for both of us. Randy

Thanks bud. Good to know we're not alone . We could start a 12 step program and talk this out lol

Man we see a ton of these threads. Who's the builder? I don't understand why a builder would not run the motor on the dyno, heck I ran mine just to make sure everything was good before I put them back in.
And we found a bad injector, and a couple fuel leaks. Much easier out of the boat to fix.

Sorry to hear your luck.

on your question about fuel wash.
was there a gasoline smell to the oil?
rings break in rather quick.how much seat pressure on the valve springs?sorry for all the ??'s.
I agree,break in oil w/ a zinc additive,run it for 25mins at 2200-2500rpm and its good to go.

Break in oil alone is a gamble if you are running performance springs. Either break it in on the outer springs only or run break in rockers at a reduced ratio to reduce pressure on the lifters.

I get it now, this must be a 575 SCI which is why it is running a flat tappet. I can't believe any competent builder would attempt to send a motor out like this. Add 40 degrees of timing to the mix and failure was imminent. Sorry you have to start over, but at this point everything needs to be rechecked, and don't forget to toss your cooler.

Ok, when it comes to cams need to talk to Bob M @ marine kinectics, but here's the deal as he told me when I was redoing a a pair of merc 525SC's gen VI with flat tappet cams OEM, both were going away, anway the cores the cams are ground on come from very limited sources and NO OEM uses them anymore so their little quality control with them...basicly junk, then the oil issue we all know about, although there is help now with this...so even brand name cams can fail at start up because of what they are ground on..now your issue looks oil related to me, if fuel contaminated the oil starts killing the engine real fast and does not take that much fuel in the oil to do you in, and 40 deg of timing on a blower motor...you just pulled the pin...sorry

cooler needs to be checked,,it was after the filter.so contamination will be very low.
I wasted 700 bucks once cutting a cooler open after an explosion.nothing in there and there was metal all over the motors top end.

not alone lol i destroyed a motor this year too lol long winter ahead

We'll the oil that went through the cooler isn't too bad. I got a couple fine scratches in the bearings but minimal. The splash oil is what killed it. I asked him to check the timing in my good motor. Even started it up for him, I knew it was good but wanted to double check his and my reading. He just said he wanted to put a paper clip in my ecu plug and set it at idle . Live and learn. Almost like someone was paying him to **** me over ( in hind site). The filter had junk in it big time I cut it open. I always run big merc filters . I will try this entire build myself this time. I did a couple 396s back in the day. I did a 402 in a camaro that hit 7500 rpm once about ever day for a year. Before it spun a main bearing. You know, the poly locks on the rocker arms were not even as tight as I like my washer less spark plugs.
Crane just last week began selling their own break in oil. I just hope I don't need to go 30 over and new pistons, that would suck, looks like at worst 1 sleeve then torque plate on the rest. We will see. Pfukin Pfaff .Never again! I should call Paul and let him know what happened, but he wouldn't appreciate it, but if he was still there it might be different

i liked your post , not because you broke, but because it helps knowing for once I'm not alone :)