Catastrophic 250R Failure! With Pictures!

[Chazz of Blades]

So after doing more tuning to get rid of my rich running issues which had a mystery cause, I am riding through the yard, running perfectly fine. Better than it ever had now that I think of it, I hear her go and yank the clutch hoping it didn't seize. Now of course I maintain my machines, oil changed often, fuel always mixed 32:1, always quadruple check that I put the right gas in, change plugs after every couple rides, and keep my carb tuned.

I'd been having awful rich running issues and fouling plugs, my carb was fine, my spark strong, my plug correct, my reeds correct, my jets stock and correct for my area, and my slide needle actually set one slot leaner. I could turn the mixture screw to almost no fuel and still run rich surprisingly, these symptoms sound more like they belong with a lean condition!

So anyway, I get that halfway fixed with diligent amounts of tuning and tweaking, have it running amazingly and fully warmed but after a warm plug check it's still a bit rich and the plug is wetter than it should be. So I ride around the yard for about 10 minutes before said failure happens.


Pulled the plug afterward and it was dry as a bone and a dark grey, so not badly lean or anything!

The cylinder is fine, thankfully, a bit of nicking at the very bottom but good everywhere else, not galded or any other signs of lean, and it wasn't dry either. The ignition chamber took a bit of damage, but nothing some smoothing and elbow grease won't fix.

The piston on the other hand SHATTERED. The skirt is gone up to the wrist pin, and there is a ton of buildup on top of the piston, but strangely the piston isn't that badly damaged on top to make up for that extreme amount of metallic bits. I'm sure my bottom end is trashed too.............


It was fully and properly warmed, and never got out of third gear in the yard, this amazes me. 100% sure it had correct mix in it, crankcase oil proper, everything I know of.

[El Camexican]

Wow! That looks expensive. Hard to tell, but I'm guessing your piston let go (unrelated to jetting) and ground up inside the cases and pushed the shrapnel up into the combustion chamber. Must have made a heck of a racket.

[tecat-z]

Yep, pistons only have so much cycle life regardless of jetting. They eventually become loose as does the bore, and the skirts develop hairline cracks that if left unchecked, will fail. I've seen this happen on a few occasions. Completely unrelated to jetting.

[Chazz of Blades]

Surprisingly, there wasn't much racket at all. It started, and ended(seized) probably within three seconds.

[CRAZY70MAN]

Holy S@#$!!!!! Freakin grenaded!!!

[rjs89ia]

this happened to the 86r that i have before my friend gave it to me. couldnt get it to idle for crap then the first real time he went out and did some riding the piston grenaded. we took it back to the house and tore the top end off to find much the same scenario. so after it sat for a year he gave it to me, still waiting to put the engine back together tho

[El Camexican]

Surprisingly, there wasn't much racket at all. It started, and ended(seized) probably within three seconds.

Usually the first sound you hear is a “click”. Sometimes that’s it, other times all heck breaks loose and scares religion into you (i.e. con rod repeatedly slapping a frame tube at 140mph while oil pours onto your rear slick that you are certain is about to lock-up when the crank stops turning. Never did get the stain out of those shorts…). I remember one “click” that lasted a millisecond, but resulted in a severed crankshaft, broken cam chain, two broken cams, 8 bent valves and two cracked pistons. It was so quiet and fast that the starter guy (it was on the start line at a drag race) laughed and said “Did you run out of gas?”

Bottom line is you’re OK and somewhere out there are replacement parts with your name on them. I for one look forward to seeing the rebuild thread

[Blown 331]

Happened to me as well. I ended up buying another engine. Pieces of the piston skirt wedged between the crank and both crank case halves and pushed the cases out. The whole thing was junk, well there were a few good pieces left but not much.

[JasonB]

never had that happen! I have had 3 84 air cooled R motors lock on me from poor jetting (most likely crank seals (need to blame something other than myself lol ) ). Nothing like riding and hearing those air cooled engines lose compression will you caost in gear to a stop. Sorry man, looks like you need to rip the engine completely apart to make sure you get all those shards out of the bottom end. good luck!

[El Camexican]

never had that happen!

Dude you just invoked the wrath of the Speed Gods with that comment! It's no longer a matter of if, but of when...

[Chazz of Blades]

Well, it took me two years to be able to afford an R, and two months before it decides to grenade.


Yippee.

[El Camexican]

Well, it took me two years to be able to afford an R, and two months before it decides to grenade.


Yippee.

"Speed costs money, how fast do you want to go?"

[Gripit'n'ripit]

Had something similar happen to an RM dirt bike. Bearings at the bottom of the rod gave way, piston went up, busted up, then went down and busted the skirt. Gave very similar looking results.

[oscarmayer]

doe the head look like the piston was hitting it? the parts need to be checked by a pro hop to determine what happened. i am willig to bet the crank bearings were worn and the pisotn hit the head causing it to crack and go, or causes detonation and that caused it to grenade.

[atc300r]

Once they get alot of time on them and the piston wears the skirt usually breaks.Iv had this happen a few times.A friend had a blaster do it last year .Still had good compression .It wore out of round.He wanted to just put in another piston.I talked him into redoing the whole lower end.Cost more .But its like a new engine now.