Home Forums Hunting & Shooting Hunter's Campfire What would cause this bike motor to grenade like this? few carnage pics

1st off lesson learned NEVER buy somebodys project bike.

Its a 02 ktm520sx with the factory 540cc big bore kit. 4speed transmission was swapped out for a MXC transmission (1-4 is close ratio 5-6 is wide) It scoots.



Slapped my steering damnper on it and Rode it for a handfull of rides with out a hitch Then a few miles into a ride I hear a light clatter noise almost like a valve thats a lil out of adjustment. No big deal, 10minuet fix. I spin around and idle back down the road to the truck. The noise starts getting louder, Then about 1/4 mile from the truck KERKLUNK she locks up. Pull the clutch and coast it to the truck.

All fluid levels were fresh and fine,

Heres what I found.

Piston was sideways and had hit the head like that bending 2 valves as well as jamming the plug inside itself.

and then (this happened at idle!)


timing cover/ left side


Right side





Oddly enough the rod looked fine,as did the entire bottom end. Any ideas on what could cause it to nuke like that.

Wow!

Compression was good? No piston slap before it grenaded (on other rides I mean)?

You get ALL the luck!

Looks like an object got stuck on top of the piston and went from there into the cylinder wall and then kaboom.

What did the head look like?

Hard to say w/o seeing more pics, but my guess would be the bearing on the little end of the con rod failed causing the piston to fail. As to why the bearing would lock up, it could be that it wasn't receiving enough lubricant or when it was assembled it was put together dry which caused it to gall over time and eventually fail.

I know it's too late to mention it, but when an engine makes a noise it shouldn't, shut it down immediately.

Sounds logical, once the piston couldn't rotate it ground it's way thru the cylinder wall.

May have had a port divider (vertical bridge separation) come loose from the big bore kit. Exhaust port, maybe?

Head had two small shallow lines/scores from the side of the piston, bent 2 of the valves. worst part about the head was getting the plug out after it was shoved inside itself.

Might add this happened a few months ago and its up and running again, just bored and got to wondering....

Jeff that thing had lots off compression, definantly not that.

Oh our crew spent 7 hours on the side of the road waitin for a damn tow truck last night after the 7.3 in the ol ford took a schit on us. Hell the tow truck broke down near prospect on the way to get us. I was only a passenger though so I cant be blamed this time (finnally )