Hole in Piston?

[beetlespin]

I have had a nightmare experience with a used boat I purchased a few months ago with a 1999 Mericruser 3.0 L I/O. The boat had apparently set unused for 2 years.

After having it tuned a second time (this time by trusted professionals at Stevens Marine) it ran like a charm (no stalling, no backfiring, much better power and no dieseling)… for a while any way. Then it started knocking (like a loose rocker/valve) then stopped firing on one cylinder.

Back to the repair shop, who found one piston had a hole in it. Even after I get it back, I’ll be afraid to run it until I call get a good understanding of what could cause a hole to develop in a piston.

Can someone help me out with this question? Before it was tuned the second time, I had added to the gas, 2 bottles of Gumout octane booster to help with the dieseling and 2 bottles of Heat to offset possible water in the gas and backfiring. Both were added per instructions. Could the combination be the culprit?

Thanks for your help,

Mike

[nobrownline]

could be caused by running to lean but more likely too hot of plug

[lingslayer]

Pistons end up with holes for a variety of reasons. Without seeing the piston it could be a number of things.

The first is a burnt-though hole from running lean or too hot of plug or carbon causing detonation. These are sometimes caused when the piston starts out with a small crack (again, detonation) and hot combustion gases are allowed to escape though it during the power stroke.

The second most common is a hole "punched" through it (read broken piston) by foriegn material in the chamber like a nut, screw or water. Did the shop check the exhaust manifold for water leaks?

It's always good to remove the plugs, add a little oil and spin an engine over with the starter after it has sat for an extended period. This will usually eject any small amounts of water etc. from the chambers.

I don't think your additive cocktail did it, unless you mixed them in VERY high ratios.

Good luck
Jamie

[1pump]

Holes in the top of pistons are caused by detonation 99% of the time. Detonation is usually caused by advanced timing, high compression, lean mixture, bad gas, or any combination thereof.
Which cylinder was it? Crank flex or twist can throw can throw the timing off on one hole, causing it to detonate. It happened to me once, but it was on a hi-perf 2-stroke.
Was the hole in the top of the piston or were the ring lands blown out?
If the piston collided with something, like a valve or debris the the cylinder, you'll be able to tell pretty easily (usually).

[beetlespin]

Thanks for the suggestions.

I don't yet know where the hole was located but I’ll get that info from the ‘shop’. The ‘shop’ told me they didn't know what caused it to fail. My web search also suggested timing or lean mixture will burn a piston.. I just had it tuned by the same group that is replacing the piston (~$1500). After their tune up, it ran great, very peppy, up to 4800 rpm for about 20 minutes then there was a knocking sound (not pre-ignition more like a loose lifter). I checked oil and it was fine. It ran ok for a while (15 more minutes) as I headed back to the launch. Then the #2 cylinder stops firing. At the launch I removed the cowling again and there was oil sprayed everywhere; even on top of the value cover.

I’ll find out more when they replace the piston and I’ll post their conclusion. I’m particularly interested in what caused the knocking before the piston blew. Any guesses?

Mike