Cylinders

[cosmo440]

Hopefully for me, its 3 times lucky. The last build was great, started on about 5 pulls when it was cold, full choke. Started on one when the engine was warm. No hesitation when you punch it from dead stop, just ran great. This is the last time I rebuild it, if it fails it goes away, far away, don't have the time or money to fix it after this.

[HoosierDeereMan]

If you snagged a ring in a port and the wear tolerances are that close to being in spec, did you check the chamfer in the ports? If there is little or no leading edge around the port area to help the ring jump the port bad things like this happen!

Troy

[cosmo440]

I think I know what happened. I took a closer look at the piston and noticed that the pin that locates the lower ring is broke off. If you look at the pic of the piston, you will see a notch between the ring lands, this is probably where the pin was forced up, breaking the upper ring and piston. The weird thing is that the pin is located on the opposite side of where the damage is. The lower ring was probably spinning on the piston with the broken pin in the gap until it got to the exhaust port and then found a way out.

[That Girl Racing]

Your observation is probably correct. But............ it is normally detonation that causes the locating pins to come loose. Which gets back to a lean condition. Do you drive the sled at steady mid range speeds? Sometimes a lean spot in the mid-range calibration causes this. You don't see it when you are an "on and off the throttle" driver.

[cosmo440]

I don't drive for miles on end at a certain speed, even on my Polaris. If I am cruising I always give it bursts to speed things up. The day the motor blew there was cruising and wide open. All the parts(jets, needles, etc...) were all new and the carb jetted by the most up to date specs I could find. This may be just a freak thing, I had a JDX-8 that had a piston pin clip come out and take the motor out, other then that the sled ran great. On the JDX-8 the clip was still in the groove, a small piece of the clip actually broke off and took the cylinder and piston out.