piston/sleeve problem

[exrider23]

Ok my friernd was going down the road and we heard a pop...well the engine died and wouldnt start, it made a terrible sound when we tried to start it....well we stripped it down and he dropped the exhaust valves..how could this happen? well we got down to the piston and the piston was pitch black and u could see where the exhaust valves hit it...well we took the piston out , then examined the sleeve ...there was about a 3 inch crack in the very boottom of it...what could have caused this? should we split the caases and take a look. btw , this is a 440

the questions:

why did the exhaust valves drop? (the clearnce was right)

Why did the sleeve crack at the bottom?

[enduro400rider]

how was your freind riding it? if he was running the balls off it that could have something to do with it. pistons usally have some black on the top the is pretty much normal. the sleev could have cracked because he droped a valve it is put alot of stress on the cylinder, or it might have heated up too much. i dont know if you built your 440 or not but if you bought it that way then the original owner could have had an over-bore 440 which is boring the 440 over the reccomended limits. i had one it my 440 and the sleev was almost paper thin.

[atvracer980]

Did the head have oversized valves ? Is he useing the stock rev box ? Were the valve springs and retainers still intact ?
I just recently did the same thing- my issue was I had LRD install oversized valves plus I run a curtis sparks unlimited box- I basically floated a valve, which with oversized valves there is no tolerance to speak of between the valves and piston unlike stock valves, the valve hung open just alittle too long and demolished the head and cylinder.

[GPracer2500]

What was the compression ratio of the pistion and what gas was being used?

[exrider23]

it is a 11.1 piston.....he was runing unleaded gas...had the stock valves and springs...the exhaust valves were BENT when we took them out...yes it is a stock rev box...

[PismoLocal]

Sounds like stretched timing chain if you ask me. I'm guessing your timing must have been off if your piston came up and smacked your valves.

[exrider23]

Ok so how did the bottom of the sleeve crack then?

[DieselBoy]

Originally posted by exrider23
Ok so how did the bottom of the sleeve crack then?

That's what I'm wondering... Easily the cam chain could have slipped a couple, but the sleeve cracking makes me wonder.....

my heart would sink of that happened, lol

[exrider23]

yea I feel bad for him..lol...anyone know why the sleeve cracked?

[PismoLocal]

Was your piston siezed in the cylinder?

[quadracer500]

how old were the valve springs? if they were weak and you were running it hard they may have floated and hit the piston.when i
checked mine they had sagged over 2mm.

[DieselBoy]

But he wants to know why the cylinder cracked at the bottom.... the valve hitting the piston was already established...