The piston area of my Blaster has started to knock consistently when running and increases when I rev the engine. The bike still runs pretty strong but something is obviously wrong. I was thinking of rebuilding the top-end, any other suggestions or experiences with this problem?

 

Sounds like piston slap, in other words, the skirt (bottom) of your piston now has enough clearance that it actually hits the sides of the jug, instead of smoothly going up and down. This is due to cylinder wear, rings starting to go,it is normal, just the motor showing its age ( or lots of use). Best thing is to get the jug off, find out how far out of round it is, bore it to the next piston size, and you are good for a long time. Pretty cheap and easy to rebuild the top end on an air cooled 2 stroke. I did my son's liquid cooled snowmobile twin cylinder in a couple of hours once I had all the parts together. If you run it too long like this, you will probably break a chunk off the skirt of the piston, and then you will have pieces of metal bouncing around,and may cause some serious damage.

 

I'm assuming the jug is the cylinder?

 

Yes, That Jug is the cylinder. If you search ebay, A guy was offering 40.00 to bore then hone the jug and 15.00 to mail it back It is best to send him the new piston and jug together for the best fit. I have a 96 blaste rthat ran, made noises and was blowing alot of smoke. Once i removed the jug, The skirt from the side of the piston was missing and in the lower gear case. I had 110 PSI so you never know until you open it up. I was suprised the thing ran.

Chuck