melted left piston, jug lightly scored...

[Stomp77]

I just rebuilt using top notch stuff 4 months ago. vito's piston's TDR crank, etc...The guys who bored and honed my jugs left visable scores but i was unable to feel anything and was told this is normal (is it?) so i assembled my powerplant and went riding. 4 months later, here we go again! Now shee's headless. The flame pattern on the pistons looks very strange to me. the intake and transfer ports have left some "clean" places and there is some light melting of the lefthanded piston. I'll post pics tonight and y'all can maybe help give a diagnostic. The left cylinder lost compression down to 45 psi. The right cylinder still reads at 128 psi. The weird thing is the side with most compression the right side has more wiggle than the side that has almost no compression FUBAR. oh yeah, does anyone know about crankshaft seals. If i lost the stator side seal would the right hand or opposite piston still have compression or would both sides compression go down? I think it would but dunno. In other words should i split the cases and replace my crank seals or just rebore and hook her up with some new wiseco's a bore job and i'll be good to go? any advis would be greatly appreciated. thanks all, chuck. Edited July 12, 2004 by Stomp77

[SDD]

Sounds like you lean seized and had a little detonation. The clear/clean portion of the piston is normal if it's right where the transfer and intake ports are. Did you have any problems with it running out of gas recently? What type of fuel are you using? What timing are you running? How much compression?

[XTShee]

:The guys who bored and honed my jugs left visable scores but i was unable to feel anything and was told this is normal (is it?)

That was probably just the cross hatching, ment to help the rings seat better or something like that

Edited July 13, 2004 by XTShee

[Stomp77]

The compression is 128 normally using a stock head at 700 ft above sea level. +4 timing advance using the ricky stator. I run 93 octane with amsoil at 50:1 with a mixture of jets. ranging from 270 to 300 on the mains. I had a carb cap come loose during a 2 hour ride, then right after that a spark plug blew out of the jug whle riding on the side that lost compression. This is the second time i have rebuilt in 4 months. The 1st time i exploded a piston in that same left cylinder and had to replace the crank and rods and pistons. I bored 20 over stock and there were still deep scores in the cylinder wall after getting the jugs back from the shop, you could see the old scratches but not feel them. Now you can feel them again and the piston on that side is covered with a lot more carbon than the "good" side cylinder. The only thing i did not do during the last rebuild was measure the rings end gap clearance. They were vito's power piston's. with a shorter thicker skirt. I wonder if the rings ate into the wall of the cylinder causing blow by and loss of cylinder pressure. Anyone know if loosing a crank seal will make both cylinders loose compression or just one?

[XTShee]

I had a carb cap come loose during a 2 hour ride,

Is this on the same cylinder that is now fuct, from memory I think reas11 fryed his GRR engine because this happened back around the start of the year.

[SDD]

I had a carb cap come loose during a 2 hour ride, then right after that a spark plug blew out of the jug whle riding on the side that lost compression.

Blowing the spark plug out of the head while riding it is a sure sign you had serious detonation issues. Take the timing back to stock or run higher octane gas. You'll be doing another rebuild every couple of months if you don't. Do a leak down test when you get it rebuilt and make sure you don't have any air leaks.

[itsaripper]

If you loose a crank seal only that side runs lean. On the banshee you have basicly two seperate engines using the same crank. If the left seal leaks you will fry the piston, and there is not much warning. If the right seal leaks you start smoking real bad, on right bank,(burning trans fluid) or fouling plugs. If you need more octain ether side can detonate and blow.

When the plug loosens up and blows out you almost always have a detonation problem. Maybe the 93 octane wasn't as high as was advertized. Did you have new gaskets on the intake track? If there was a leak by the reeds or boot, you could burn a piston.