1994 ski nautique engine rebuild help

I need some advice rebuilding this 351w pcm pro tech ecm ( carbed) engine. I recently went out for a ride on afternoon and noticed a miss lack of power and smoke coming from the hose I top of the valve cover. At first thought I was thinking clogged pcv valve or inoperable for that matter but upon further inspected of a compression check I doing that the number two cylinder had zero compression and all other cylinders averaged 120. After speaking with a number of people and trying to pinpoint the exact cause I found that the top of the #2 piston was missing a small chunk out of it and it looks as if something had either fallen Into the intake or just old age I'm not too sure yet. This is what I know right now, this engine is from what I understand half way converted from a protech fuel injection to ecm and carb. Since I bought the boat I've wanted to put finish the conversion and buy the kit from ski dim to make it a distributor carb engine and eliminate all possibilities of having problems with the ecm In the future and cleaning up the Intske so it's not cluttered with unused plugged originally meant for the throttle body. I also understand that the carbed version of this engine is a drop In horsepower but since I'm doing the rebuild I'm wondering if I can gain a little in ungrades like maybe a new cam style? This engine has the three bars on the heads which is gt40 and I'm having them gone through and looked at along with the block this week. Is it worth boring out the cylinders? What Pistons and rings should I go with? And other upgrades that might help I have not yet covered would be helpful?

That is classic detonation damage. Not unusual at all.
The main cause of detonation would be over advanced timing.
A lean cylinder could do this also. Intake/pvc air leak or a failing fuel injector but you did say this was carbed. Lean cylinders burn very hot. The extra heat makes the gasoline blow up at the wrong time, way early. Your head gaskets could be damaged also.
Crossed spark plug wires or bad spark plug wires that are cross firing is another cause of detonation.   Any time the gas ignites too early the piston is trying to go up in the cylinder and the fuel explosion tries to blow that piston back down while you have 7 other cylinders pushing it up. This creates extreme pressure in the cylinder and breaks parts. Detonatation
Normal pressure in a wide open 351W might be 600 PSI at the fuel explosion.
With detonation that same cylinder can see 3,000 + PSI and that starts breaking parts.
The piston ring under that piston fracture is most likely broken also.
Since your problem is only one cylinder, check your spark plug wires for Halo's. Small white halos indicate spark jumping through the plug wire.
Inspect your intake gaskets very close and measure them to make sure they had even clamping.   The leak if you had one would have been at the intake port for that cylinder.
Fix the problem before starting the engine again.   More than once I have seen guys repair the damage and then repeat the failure because the problem was not fixed.
There could be 10 more reasons for that detonation but I listed the most common.
Hope it helps.

A local highly respected engine builder around here got a set of the Flotec heads to check out. He was not impressed in the least.
I don't think you want to hang those heavy cast manifolds on aluminum heads anyway.
I can say with experience it takes big$$ to make big ponies.
But if your just looking at heads, intake, cam that's not to pricey. You already have a descent set of heads so a cam, intake, carb and a good distributor will get ya smiling for a little over a grand I'd guess.

Duane in Indy wrote: gun-driver wrote: A local highly respected engine builder around here got a set of the Flotec heads to check out. He was not impressed in the least. I don't think you want to hang those heavy cast manifolds on aluminum heads anyway. Bolted on with the proper length bolt and proper grade bolt and proper torque then there would be no issue. Using about 4800 rpm for our use, look at the comparison by this independent source. They state best $$ value. You'd be hard pressed to equal $ in GT40P heads or even GT40 IMO       and we all know what opinions are worth without data to back it up. http://www.hotrod.com/articles/ccrp-1302-six-budget-ford-heads-that-work/ Duane

Here's the link to Duane's backup to his opinion.

I'm working through this same motor combination right now.   I just did the protect/EFI conversion to carb and DUI distributor.   you don't need the ski dim kit, it's more expensive than the DIU performance distributor, and the wiring is really very simple (once I got past the unknown of removing the TBI/EFI wiring) .    In my research, I have found that you can get a GT-40 long block from summit racing for ~2300, and after several machine shop calls yesterday, it sounds like machining + parts is going to be in the same neighborhood for me cost wise.     it might be worth looking at a long block or short block as a base, unless you really are wanting to do something custom or out of the ordinary.    Summit is where I got my DUI also, just add it on at the same time and be done with protec issues .   

I'm going to see that the machine shop says and go from there. aside from getting rid of the pro tech system i basically just want to tweak the engine just a little if possible maybe a dif cam size or an intake but from what I've read the intake is tricky because I'm already maxed on clearance from the engine cover and most after markets are taller..

More items in your picture. The piston is scuffed (black scratches by the piston pin)
This tells you the piston head was very hot at failure. Roll it over and study the inside.
The under piston head will be discolored. From excessive heat.
Piston head heat will heat the piston pin bosses making the piston skirt scuff by the piston pin like yours did.
Now look at the underside of the other 7 pistons. If any or all show heat it will tell you how many were running hot before this failure.
Your coolant temp gauge can sit rock solid at 140 while the combustion chamber temps are seeing extreme heat.
Find out how many cylinders ran hot and then determine why.
I am disappointed your machinist did not know the cause in two seconds after seeing that piston.

I'm suspicious of some malfunction in the protec bank of coils fired that jug early, and wouldn't run your new engine without a proper distributor.

So the machine shop called and reported that one head was cracked between the two valves so now it's to plan B. Now I'm looking into buying a long block. With the purchase of new heads there is no way to justify cost wise. Probly gonna go with summit on this one. So with that being soar I have a protech ecm for sale and one head and a block that can be be bored over. I'm really thinking over fitting rid of the Holley 600 and going with the quik fuel 600, that with the distributer and possibly new intake should put over 300 hp

to my knowledge the oil pump won't come on the long block do you can buy which ever oil pump you need too, I thought about using my take off but I'm gonna go new just Becusee its too much of a pain to replace if it goes out. There is a local company here in Houston that sales reman marine engines called thunderbolt, I'm gonna call him Monday and find out more about the exact process and if they actually built the engine or it comes off the shelf from another distributer. They have two companies listed on their website that both sale marine engines. List price they have is 1570.00 with core but I doubt it comes with gt40 heads but I'll just have to wait and see. I'll pay the extra money to have them exchanged. I've been looking into the dui distributor and quik fuel 600 carb to replace my Holley now i just need to figure out the intake. Use original take off or buy aftermarket? They also offer a boil service at thunderbolt to remove paint and Rust from all my old part like water pumps, impeller pumped, bell housing, brackets and so forth to bring back to new so I can repaint to follow my paint scheme of my 94'. I'm thinking of going with dark ford blue and get away from original. Where can I find a oil pan that is this size besides ski dim?

It's has a pretty bad. Rust spot on it and I'm not sure just how bad it is just yet until I get it cleaned up. If it can't be fixed and the metal is too weak I will have to order another one and just want to be prepared,

rrman01 wrote: ... not sure why the pics turn sideways, how can i fix this

Looking good.

Did you take the pics with an iPhone? Apple has their own funny eco system with the pictures. I researched it once and of course, they claim they are right and everyone else is wrong.

Anyway, either with your phone, or if you save the picture to a computer desktop, just open the picture in an edit mode. Even the most basic editing tools, like "Paint" on a PC, will usually let you rotate a picture in 90 degree increments.

Looking good. Really like the valve covers!

Congratulations on the install and fire up. If your engine is a roller cam engine it is good to go. If it has flat tappets you need to break the cam in, maybe this was already done but it is absolutely necessary for any flat tappet camshaft.
Break in means you take the RPM up to 1,500 -2,500 for the first 20 minutes of run time.
This gets your lifters spinning properly and allows them to break into your camshaft.
If not broke in this way many flat tappet cams go flat and fail.
The engine looks fantastic, nice work.
Is your air cleaner Marine approved? It looks much better than the Marine filters I have seen.

If it runs perfect the only danger at this point is getting hot. After the first hour I would not be afraid to open the throttle but I would not keep it there more than a few seconds, less than 15 seconds, should be enough to get some idea how it pulls top end. Running hard heats the internal parts and a new engine will heat far more than a broke in engine so be careful but enjoy it. After the first hour I would ski if I wished but not barefoot yet. Maybe after 5 hours. Be conservative on the timing factory specs are perfect, extra timing makes extra combustion heat. and you don't want that. Enjoy now