Piston scortched

[FULL-THROTTLE]

I also posted this on my "rave cap melted" thread:


98 Challenger twin 787's:

I just pulled the motor and I found both pistons and cylinders severely scuffed/scratched and both rings on each piston look like they are stuck.

The engine had a full tank of premix 25:1 with the oil pump operating and the throttle never went above 1/2 throttle, I ran it for 20 mins and let it cool for 30 mins for the entire tank. then with the second tank I did not stay at full throttle very long. I only went through 1/2 of the second tank when I found the rave cap melted, and now bad pistons and cylinders.
I confirmed the oil pump is working when the engine was running by pullling the oil line going into the intake and I could see the oil pulsing/pumping.

What the heck is up with this engine, it only has 6 hours on it.

any help is appreciated.

 

[unclejay]

Spark PLugs

What do the plugs look like ? Thay should tell the whole story, although it will be a little muddled since you probably idled back to the dock. A proper plug check has to be done from high RPM and then chop the ignition.

Anyway, your situation sounds like extreme lean running condition, which would be evidenced by:
- White flakes around the insulator
- Damage to electrode or metal deposits on it
- White ash around the top of the plug
Ignore the threads

Cause ? Fuel starvation most likely. Air getting in carb or manifold, crack in exhaust near the head, improper jetting of carb.

 

[FULL-THROTTLE]

Plugs

The plugs are wet and black, there is no buildup. the plugs were new from the initial startup and I only put approx 6 hrs on it. The engine was/is running fine the rave valve cap was melted and I saw the pistons when I went in to pull the engine. ???????