That was a steam cleanin if I ever seen one! None the less... you need to find the root cause. Just identifying detonation as the reason will not fix it. There are many things it could be, and you will probably never have a definative answer. Therein lies the challenge (and satisfaction) with the with our sport as do-it-yourselfers.

Good Luck

BT

I know it sounds stupid but look at the balancer some are marked at 0 and 30 and sometimes the paint can get thick enough to cover the 0 mark, also make sure it has not spun off TDC. 90 + % of the time if the spark plug electrode is gone so is the piston or valve . I dont think your gills are leaking.
Just a thought

This board is a real eye-opener for me...Every time I see one of these monster engine boats going by that cost big $ to buy, I usually see some candy-ass kid driving it. Talked to a Cigarette sales guy once and he explained that alot of businessmen buy their kids $200k boats so that they'll be too busy playing to screw up their father's business.

Realizing that there are hard-working people out there breaking these things down and putting their blood, sweat, & tears into their engines, it makes me proud to be a humble gearhead.

And to think that I thought that a bad day was a little high on the temp reading.

Good luck, keep chugging...who needs sleep anyways?

The good thing is, I love wrenchin on engines almost as much as I love the sound of 2 of them at 5400 rpm.

That motor only had a few hours on it. That might account for the cleanliness of it. Just another guess.

Also the intake was made for a dominator. The center cylinders seem to have the toughest corners or the furthest to go. I don't know how much that would effect it.

All the valves in the center four cylinders have tuliped valves to one extent or another.

The carbs are probably jetted to low with #78's.

The fuel was half bad and half Premium 92 octane, so I had at least 82 octane right?

Hey, my boating season may be over, but at least when I'm done, I'll know the motors are the same, and done correctly.

I checked compression on the starboard engine and got these results;

1 - 155
3 - 150
5 - 150
7 - 150

2 - 150
4 - 148
6 - 135
8 - 150

I think both motors are still gonna come out just to make sure they are both the same, and to freshen up.
I guess I still need to make a decision on what caused it.

I think I'll put in some #84 jets and back the timing off to 30°. Empty the tanks and refill with new. Say a prayer and see what happens. Whattya think?

Jim,

Do you know if those were inconel exhaust valves? If they were not, or you are not sure, you might consider going with them on the rebuilds.

Yes, it had inconel exhaust valves. That's exactly what's going back in too.