dtsquest

I'm no expert, but wouldn't bad gas cause a problem with more than one cylinder? The same gas would be flowing into all cylinders, which should cause damage to more than one? I'd be checking the flow of the fuel before I had it all back together.

Wobble

Linster,

We are going to re-CC the heads etc and get exact CR. He said they are big chamber heads. I will post the data when I get it.

Mikes280,

We have inspected the other pistons closely. No sign of detonation or heat damage at all !!!

However, the cap is very dusty inside and has an oil film on part of the inside. There might be a faint track between # 2 & #7 hard to say. Definitely will be getting new cap and rotor. It is a complete MSD marine system (billet dist, 6M, red wires etc) with the soft touch limiter. The oil film was probably from the motor breathing so bad after piston holed.

Patriyacht,

Thank you for looking that up. If my engine builder is getting irritated with my questioning his work, he is not showing it yet.

dtsquest,

exactly, thats why we are stumped, so far.

The bearings should show damage if it had been detonating for a while. He has measured them all and says they do not need to be changed. A motor that has been detonating for a while normally hammers the bearings.

We know that ceramic piston top coating helps hold off detonation a little, but that doesn't explain only #2 damage.

Also, the gas was bought at an off-brand gas station. I filled it to the neck and stored the boat. It is possible that the octane wasn't as advertised as there is a lot of money to be made by putting 89 in the 93 tank. With these new cars it is very unlikely that it would be caught as the computers will compensate for detonation. Not that any new car I can think of requires 93. It costs $600 for an octane test and there has been to much time too make a case even if I spent the money.

Wobble

Here's an update,

The gas was undoubtably a factor but the real problem is compression. This motor came out of my 19' jetboat it was 9.8-1 compression and ran another 170 hours in my 29 Stryker before I had problems.

At that time we went .030 over for 509CI and went to full hyd marine roller setup, single plane intake, porting etc. The engine builder was supposed to change pistons to get us below 9.5-1 CR. The pistons installed actually took us up to 10.5-1

It is amazing that I got 34 hours out of it running Shell super. The offbrand gas was the final straw causing it to burn the side of the piston in #2, the ring probably stuck peeling up a piece of the ring land that landed in the quench area punching a hole in the top of the piston.

using smokemup's online calculator this is what I had

You Entered:
Bore 4.5 (inches)
Stroke 4.0 (inches)
Rod Length 6.135 (inches)
Cyl. Head Vol. 116 (cc)
Deck Height 0.0 (inches)
Head Gasket Bore 4.540 (inches)
Head Gasket Thickness 0.039 (inches)
Piston to Cyl. Wall Clearance .004 (inches)
Top Ring Land Height .310 (inches)
Piston Dome Vol. 17 (cc)


Compression Ratio:
10.525 : 1

Bore / Stroke Ratio:
1.125 : 1

Rod / Stroke Ratio:
1.534 : 1

Total volume:
1152.157 cc's

Compressed volume:
109.471 cc's

The heads have been sent off to unshroud the valves and gain whatever cc's we can there. The SRP piston domes are solid so once we get the chamber cc's we will cut the domes to get the CR down to about 9.3-1. something like this.

You Entered:
Bore 4.5 (inches)
Stroke 4 (inches)
Rod Length 6.135 (inches)
Cyl. Head Vol. 122 (cc)
Deck Height 0 (inches)
Head Gasket Bore 4.54 (inches)
Head Gasket Thickness 0.039 (inches)
Piston to Cyl. Wall Clearance .004 (inches)
Top Ring Land Height .310 (inches)
Piston Dome Vol. 6 (cc)


Compression Ratio:
9.245 : 1

Bore / Stroke Ratio:
1.125 : 1

Rod / Stroke Ratio:
1.534 : 1

Total volume:
1169.154 cc's

Compressed volume:
126.467 cc's

We are doing the heads now, what do you guys think about cutting the dome off forged pistons?

shawn

Mark, what was the temperature the day you holed the piston? Was it a chilly day? If so, you may have needed more jet with that compression ratio.

Shawn

Wobble

Sutphen30,

Yes, you also were spot on, with your photo-diagnosis. I asume you saw my other thread..

Thanks for all your help.

I was very nervous about running the motor again without finding a reason for that cylinder. a 10 cent part