Jon1

It was running great, suddenly lost power. I can see a small hole in #1 piston. Also found the spark plug was completely closed. Any idea as to the cause?

pwcpro

Your piston came in contact with the sparkplug. Bad news. Probably more than just a top end.

Jon1

I took a compression test this afternoon before pulling the head. #1=zero, #2=150, #3=150. Pulled the head found a hole melted in the piston about 1 to 1 1/2 inches in diameter. So, I suspect the piston melted, came apart and smacked the plug. The inside of the combustion chamber (the head) has some scars from pieces of piston bouncing around. I don’t believe that’s a big deal, I’ve seen lots worse. I don't know if the cylinder went lean or the oil system failed. # 2 and # 3 look great. The water jackets in the block and head are very clean almost zero scale. As a mater of fact I would say there is no scale but just some very thin mineral stuff that wipes off like chalk.

Also I checked the bore. I measured 3.165 with my calipers. According to the specs an 1100 is an 80 mm bore. 80 mm according to my conversion chart is more like 3.1496. So.... looks like this has been apart before. Maybe honed or bored .015.

I'm going to work toward getting the engine out, pull the cylinder ass'y off and have a good look. I may split the case just to inspect and clean debris.

I’m an automotive mechanic with nearly 40 years experience. I wrench my own cars and I wrench my own bikes. There are 4 Harleys in the garage from a 1959 PanHead chopper to a 2002 Fuel Injected Bagger. PWCs…. are a new game to me. The nuts and bolts of it is not a challenge. I could use some advice as to figuring out WTF happened to this engine. I know this repair is going to run into hundreds of dollars for parts. I really don’t want an instant replay. Also, this machine is really fun, lots of power, good acceleration, good top speed (60-65) depending on conditions and does really well in rough water.

Thanks in advance for any and all help.

Jon

pwcpro

I've had this problem before. In my case pre-detonation caused by twisted crank. Water hitting the piston could cause same.

123456

lean fuel condition most likely caused the failure, suspect fuel system or crankcase seals.

Jon1

I had one mechanic tell me it could be from using 87 octane fuel. Pre-ignition and melt the piston. Odd there is zero damage to #2 or 3.

ggauvin

With #2 & #3 looking good, I doubt the issue is 87 octane, but at 150 psi you might start thinking about premium gas. I assume it is stock (except for the prior bore job), so I would think twisted crank is unlikely. Yes you need to split the case... there is debris in there by now... and that gives you the chance to check the crank anyway. Lean condition is still a candidate!