My kx80 makes a knock when i start it. its coming from the piston. how can i correct the knock? ?

Question

My kx80 has a new piston and rings. i blew it up before i but them in. hence why there new. it makes a knock in the engine when i start it. whats the knock in the engine and why is it knocking?

Answer 1

Wear and tear is a normal part of our life.  The sound you mention appears to be the result of increased play in the gudgeon pin which sits in the center of the piston and connects it to the connecting rod.

See if you can ignore it, provided the motor is functioning OK otherwise.  Else you will have to open the head for inspection and rectification.

Insufficient lubrication is the cause of the trouble.  Change your engine oil periodically.  In case of 2 strokes, a correct ration of 2T oil is also important.

Answer 2

The cylinder could be worn out.

Did you check the piston to cylinder clearance before putting the top end back together?

That's an important detail when rebuilding the top end.

Did you purchase the bike brand new?

Perhaps a previous owner bored the cylinder to the next oversize.

Answer 3

a knock is not always the piston. you need to check the connecting rod on both ends and make sure the wrist pin is correct size. And it could be coming from the kick start clutch.