[Westtt80]

short story. i was riding the other day went to race my friend launched it pretty hard and it stalled. went to start it and i heard loud knocking so i shut it off.

sounded like valve to piston

pulled it down to check timing and its right on. but when i turn the motor over with a ratchet and the piston is on its way down mid stroke i can take a screw driver and push the piston down like a 1/16 of an inch

turns over fine by hand

Rod bearing isnt it?:disgust

 

[cjc]

if you push on the very front or rear edge of the piston it will rock on the pin axis making it look like there is play in the rod-crank bearing.

if it starts and runs fine other than the knocking noise, it sounds like a rod bearing going out, but usually you can feel it snagging -catching at the same point in the cranks revolution when turned by hand.

you stated it happened when you went to launch your start, it could be something in the clutch let go.

we exploded a clutch basket awhile back in the YFZ and it would still drive, but knocked like hell.
tore it down and the basket fell apart in my hands !!

on the Banshee before then had a fiber shatter and break a finger on the basket ,it rattled like mad , thought it lunched a bearing !

tear it down starting with the cheap, simple stuff first.

inspect the clutch side , stator- balancer side ,you'll need to remove those anyway to split it ,might find it's something simpler that a rebuild !

BUT I WOULDNT COUNT ON IT !!!

 

[Westtt80]

if you push on the very front or rear edge of the piston it will rock on the pin axis making it look like there is play in the rod-crank bearing.

if it starts and runs fine other than the knocking noise, it sounds like a rod bearing going out, but usually you can feel it snagging -catching at the same point in the cranks revolution when turned by hand.

you stated it happened when you went to launch your start, it could be something in the clutch let go.

we exploded a clutch basket awhile back in the YFZ and it would still drive, but knocked like hell.
tore it down and the basket fell apart in my hands !!

on the Banshee before then had a fiber shatter and break a finger on the basket ,it rattled like mad , thought it lunched a bearing !

tear it down starting with the cheap, simple stuff first.

inspect the clutch side , stator- balancer side ,you'll need to remove those anyway to split it ,might find it's something simpler that a rebuild !

BUT I WOULDNT COUNT ON IT !!!

I started it once after it happened but sounds like hell.
Also when I referring to the play in the piston I w
as pushing a screw driver through the spark plug hole

Thank you for your advice IL dig into it more tomorrow

 

[Westtt80]

well found the problem. See pics.


now my dilema is the metal that went into the motor, the little indent in the cylinder and what all should be done.

i want to go big bore but i want to do it right so what now?

 

[Terse]

Yep that would be a problem :lol

Athena kit would be the best affordable BB kit.

You will need to take apart the whole motor to clean the debris out.

 

[cjc]

ouch , that must have made a hellacious racket !!