Super Jet Root Cause: Help me diagnose a piston-cylinder failure

hondamxracer

hondamxracer

Location
Missouri
Hello,

My engine lost power last night due to a rear piston / cylinder failure of some sort.

When I pull the cylinder, what should I look for to determine if the issue was due to a seizure or a ring catching?

The engine had 9.4 hours on it with no leaks and measured between 145-150 psi at 3 and 7 hours.

Here's my specs if this helps diagnose root cause:

  • Pistons: Pro-X (718) bored within spec
  • Ported cases and cylinder
  • Thrust girdled head with 35cc domes
  • Delta Force 2s
  • Dual 38s (75 pilot, 137.5 main, 1 turn on low speed, 1.5 turns on high speed, 43 pop off)
  • Gas: 40:1 - Castor 927
  • Epic
  • Lightened Flywheel

Thanks!
 
hondamxracer

hondamxracer

Location
Missouri
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Here are a few pictures before I pull the cylinder. Amazingly, there are no scars in the cylinder above the rear piston.

When I pull the cylinder, is there an easy way to prevent any debris from falling into the cases?

I'm hoping that I don't have to pull the engine and split the cases once I repair this cylinder.
 
hondamxracer

hondamxracer

Location
Missouri
I removed the cylinder and found that it did Not seize or catch a ring. I did however find a nice crack in the rear cylinder wall. No other scarring which seems odd.

I believe the crank is the issue, as it barely turns over. I"m not sure how many hours it has on it. This was the first rebuild since it was new from the factory (2001 RN).

Help me understand what went wrong. Did the crank go first which caused the damaged to the cylinder or vice versa?

What caused the crank to go bad? Simply wear and tear?

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I'll post up some pictures of the crank and cases next week once I split the cases.
 
Last edited:
TheBuzzard

TheBuzzard

Location
the jetski grave yard
when i saw the pix in your second post and saw the tiny dings in the dome, something went thru your motor. since the dings were tiny i figure a bearing cage is falling apart. take the pistons off and check the wrist pin bearings. if it aint those then its gotta be crank or rod bearings. bottom line is, its :):):):)ed up and needs everything.
 
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