Something let go.....

[Kny21]

Ski took a dump on me last w/e.... was starting to act up out on the water but not too bad but decided to head back anyway. 100 yards from the ramp it cuts out... starts back up with a little throttle love but proceeded to cut out again right after planing out. Knew it was bad so got a tow and pulled the plugs, back plug had some material on it and a quick thumb compression test couldn't break the seal. :rocketwhore:

Pulled the head and cylinder and this is what I found..... back cyl was beat with chunks of itself, rings, and what looks to be wrist pin bearing or two.

Whatever was bouncing around ended up cracking the sleeve in two spots.

Front cyl looks good except for the piston top by the exhaust port looks like it has something going on thats not related to the rear letting go and damaging it.

Any ideas what could of caused all this? Because of the front I'm seriously doubting this was a fluke and don't want to rebuild to have it crap out on me again.

 

[SUPERTUNE]

You better find out what your doing wrong with the tuning set-up! You have some bad detonating going on and I'm sure that caused the major damage to the rear cylinder!
All things need to be looked at... air leaks, compression and squish, ignition timing, carb jetting, and don't forget to look at the exhaust system and cooling system.
TEAM SCREAM RACING
1988 Carroll St.
Clearwater, Fl. 33765
(727)442-7700

 

[SuperJETT]

Detonation ate away at the exhaust port side until it finally collapsed and broke away.

Too much timing, too lean, too much exhaust backpressure, too much compression, too low octane for the setup, or a combination of several of those can do it.

 

[Kny21]

You better find out what your doing wrong with the tuning set-up! You have some bad detonating going on and I'm sure that caused the major damage to the rear cylinder!
All things need to be looked at... air leaks, compression and squish, ignition timing, carb jetting, and don't forget to look at the exhaust system and cooling system.
TEAM SCREAM RACING
1988 Carroll St.
Clearwater, Fl. 33765
(727)442-7700

Detonation ate away at the exhaust port side until it finally collapsed and broke away.

Too much timing, too lean, too much exhaust backpressure, too much compression, too low octane for the setup, or a combination of several of those can do it.

Motor hasn't really been touched by me since I've had it for 2+ years.... the only things I've done was added dual cooling and FCV to help clean up the bottom end. I did lean out the high about a 1/8 - 1/4 turn but plugs always looked good and ran fine all summer.

Compression is right at 175 (or 180?, can't remember) with the 35cc domes and I've always ran high test (93). I haven't pulled the front cover yet so I can't speak for timing, but I'd wonder what took it so long if something was wrong?

What would I need to look into on the exhaust or cooling? I don't understand how I'd have too much exhaust backpressure, etc. It's got a B pipe but I've never touched the screws b/c they're frozen.

 

[SuperJETT]

Motor hasn't really been touched by me since I've had it for 2+ years.... the only things I've done was added dual cooling and FCV to help clean up the bottom end. I did lean out the high about a 1/8 - 1/4 turn but plugs always looked good and ran fine all summer.

Compression is right at 175 (or 180?, can't remember) with the 35cc domes and I've always ran high test (93). I haven't pulled the front cover yet so I can't speak for timing, but I'd wonder what took it so long if something was wrong?

What would I need to look into on the exhaust or cooling? I don't understand how I'd have too much exhaust backpressure, etc. It's got a B pipe but I've never touched the screws b/c they're frozen.

Any chance you changed the amount of water going into the stinger by adding the fcv? More water would make the effective stinger size smaller, more backpressure, hotter temps.

 

[Kny21]

Any chance you changed the amount of water going into the stinger by adding the fcv? More water would make the effective stinger size smaller, more backpressure, hotter temps.

I actually did the opposite..... originally the cooling had a line from the top of the headpipe directly to the stinger. I T'd that line and added the fcv off the 90* fitting to the stinger to help cleanup the bottom end.

 

[demolition_x]

what brand fuel were you using?

 

[Kny21]

I use whatever.... as long as it's 93. I think most the time its Exxon, but occasionally run Hess or Shell.

The fuel I was running while it happened was Shell from Jersey.... but usually I buy from MD where they still aren't using ethonal blend.

 

[Brenden]

whats your setup

 

[BlwnBrd]

????

 

[Kny21]

whats your setup

It's a mild ported 701 with single 44 (grey) on BCW(?) intake with the Riva spacer. ADA girled head with 35cc domes. B-pipe (don't know where the screws are set) dual cooling with the FCV, SN waterbox.

Since originally posting I've only checked the timing which is set to stock. Still got to look into the carb settings, etc.

 

[Sanford]

Check to see if the baffle in the b-pipe chamber didn't come off or look for a collapsed exhaust hose (stinger and out of waterbox hose). Make sure stator plate didn't move.

Piston temp got really high and snowballed.