Damaged Cylinder

[condor]

Riding my banshee wot this past weekend, she suddenly lost power.

I found the right side piston top had a piece blown off. The rings and piston are fryed and the cylinder is scored, but not too bad. Any suggestions as to whether to replace the cylinder or bore both out? If boring, what size from a stock cylinder? Should I just re-sleeve the cylinder? Anyone gone through this.....? Thanks.

[svtkid78]

BEFORE DOING THAT YOU SHOULD TRY TO DIAGNOSE THE PROBLEM OF WHY THAT HAPPENED SO IT WILL NOT HAPPEN AGAIN RIGHT AWAY. AS FOR THE BORING YOU SHOULD TRY TO BORE AS LITTLE AS POSSIBLE, BUT THAT WILL HAVE TO DEPEND ON HOW BADLY YOUR CYLINDERS ARE HURT.

[condor]

Thanks for the info. I suspect...I may have been running lean in the right side. The plug was gray. Left side looked okay though. I'm running a 290 main jet. Should probably start at 320 and work my way down when I'm back up. Going to do a compression test, and crankcase leak test before starting it.

[Blacksmith]

Good idea on the checks and tests. If only one side was lean, most likley you had or have an air leak, or a blocked main in the carb.

As for the cylinder, you need to take it to a machine shop and have them look at it. They can help you figure out what bore size you are on now, and what size you will need to go to in order to clean up the damage. When they are able to give you that size you can order a top end kit and have them bore both jugs to fit the new pistons.

After that, slap it back together and ride.

Good luck, have fun.

[.]

when you say blew a hole in the top of the piston and the rings are fried, do you mean that their is a hole burned in the top of the piston, or a chunk missing on the side of the piston and the rings are all melted into the piston?

 

If it was a burned hole....it was detonation. If it looks like theres a piece of the top missing, and where the rings go into the piston are all bent up/ piece of a ring missing/piston skirt damage/anything to that degree, chances are that you had play in your piston and caught a ring on the exhaust port and thats what did the damage.

 

The gray on your sparkplug is from the piston material.

 

Like blacksmith said, take the cylinders to a machine shop, (I believe stock bore is 64mm), find out what size you need to clean up the cylinders, go get those pistons and bring them back so he can bore to the size of the pistons.

[909]

Like blacksmith said, take the cylinders to a machine shop, (I believe stock bore is 64mm), find out what size you need to clean up the cylinders, go get those pistons and bring them back so he can bore to the size of the pistons.

Stock bore is 64mm, they go up in .5mm increments up to 66mm. A competent shop should be able to do the boring, honing, and get you hooked up with a good piston set, wrist pin bearings, and gasket set. Check the head for major damage from piston schrapnel too. You will need to clean out the bottom end as well if the piston came apart. Depending on budget you could replace all the bottom end seals to be sure its not leaking. If you wash out the bottom end and not replace the seals i'd say a leakdown before firing the new setup would be mandatory. You don't want to blow up the new stuff if the bottom end was leaking all along.

 

Good Luck!