might not make river run

Wow, my post sounded a bit negative on the O2 sensor. Not the case, great tuning tool, just not something you can run and depend on all the time in a boat like you would in a car.

Engine is in machine shop finally, came to conclusion of Iit being a detonation problem.

TX Foilhead wrote: Wow, my post sounded a bit negative on the O2 sensor. Not the case, great tuning tool, just not something you can run and depend on all the time in a boat like you would in a car.

Thats sound advice, I had an o2 sensor in my 81 ski with a meter that I could plug into a laptop and record basic a/f ratios. It worked great but for a very short while, the slightest little hint of moisture and an $80 sensor was toast. Placement of the sensor is different depending on the manifolds you're running but with logs I couldn't keep the sensor dry so once I got the boat dialed in and the sensor went bad I never replaced it again. It's a fun tool but typically once you're dialed in it's not really a necessity unless you make changes to your setup, ie different prop, jets, tuneup.

That'll buff out maybe a little wet sand, buff and slap it back in.

lakedog55 wrote: That's what I was thinking. Maybe a little jb weld. no before it goes back together. It will be checked. Was already planning on doing top end. So new plugs, and wires, also a new distributor. Intake, heads, and cam. going to try out a quick fuel carb as well. I wont be playing with the timing anymore.

Well that's just it, you do need to play with timing so I think you get it but you don't exactly get it so I'll be kind. By buying a new Dist you are playing with timing so how is it set? You don't know as of right now so find out. Make sure you know how to measure and set the mechanical advance before you even drop it in the motor. I'm guessing on your 351 that you will want 10 degrees of initial and another 24 of advance.

you're also buying an unknown carb so how is it set up? you don't know as of right now so find out. How is it jetted and what PV is in it? Honestly I would stick with the stock Holley Marine unit spec'd for your motor. Even with a slight bump in compression and a slightly hotter cam the stock holley will perform just fine right out of the box.

And let us what plug are you going to put in the P heads so we can verify the heat range.

Here's a great article about what caused that.

http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php

Incase the link didn't work. http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php

It keeps getting better. Machine shop does not want to build on my block. They are saying it is to corroded to clean. It did not run hot before. Highest temps I saw were around 165.
any ideas? Or does anyone have a block laying around?
Mike

Couple notes, that piston is classic detonation. Boat engines work hard and can't use as much timing as a passenger car. See what PCM recommends and stay close to that number for total timing.
I don't know of any O2 sensors that will work in the marine exhaust.
Reading Spark Plugs has helped tune engines for years. Check at the Champion Spark Plug web site for pictures that show reading spark plugs to help tune an engine.
If the plug run is too hot it will start to glow red and the red glow will set off detonation before the spark reaches the plug.
Too cold of a plug and it may not run hot enough to avoid fouling out.
Again, PCM has years of development on Marine Engines, follow their lead and you will avoid problems.   People jump in a boat and don't hesitate to run it wide open, sometimes for more than 30 seconds. Very few engines outside Marine are every expected to live when exposed to frequent wide open runs. For these reasons Marine engines are built to a different standard than Passenger Car or even Performance Engines.
To melt the piston like that you had two flame fronts colliding and they torched your piston. Don't focus on just one cause, your entire engine could have been tuned perfectly and still had this failure if one of your spark plug wires was cross firing into another cylinder.
Hope you get it back to perfect again soon. Good weather is coming.

Mike,
Help me understand something here. You had the block bored .20 over to start with and then put it all together once already. Then you ran it how long before the piston fragged? An hour, two hours, ten hours, more?

Even if it was 100 hours, how in the world can a block go from being good to too corroded (on the inside) in that time frame???? Unless you were running pure water where oil should have been for a long time, I just don't see how a block gets to unusable under those circumstances or am I missing something?

Gotcha. So all you did was cam, heads and intake? This wasn't a complete rebuild then? The .20 over thing was messing with my head.

The detonation that destroyed that piston may not have injured your crank, cam or any of the lower end. If that is the case you may be able to run the crank without turning it again to another oversize.
Should save you some money. The 300 hour old parts may be perfect.
New pistons, block and back in business but look hard at your old parts to find information about the failure. Your machine shop has probably seen this issue 100 times and can help you ID your problem.

not sure on distributor
its at the shop but i think they put 24 degrees in it.

Got my DUI last night. a lot less than my last one




Did not even leave the house

cam in




clearcoat on intake

Will know in the first fifteen seconds of this thing running.

Front is front, one will look upside down. Proceed.