Grenade!!!!!!!!!!!!!!!!! Warning, GRAPHIC content!!!

[blsnelling]

Time for a little CSI sleuthing. What happened to my saw?

This is my new MS440 I was preparing a little GTG surprise, and got a REAL surprise myself! This is a 046BB that I ported and installed today. I relieved the crankcase for the piston skirts, slotted the base mounting holes, ported it, and had it back together running. I fired it up, tuned the L a little, and let it set on the ground idling for about 5 minutes. I then walked over, blipped the throttle, and BAMMMMMM. It was barely above idle when this happened. She made the most aweful sound and locked up. There was no wondering about this one! I pulled the topend, and this is what I found.

I'm not 100% what failed, so your input is appreciated.

 

[blsnelling]

 

[blsnelling]

 

[HittinSteel]

I'm gonna go with nuclear warhead over the grenade theory

 

[blsnelling]

I was very concerned about the bottom end of the saw, particularly the rod. I turned the saw upside down and put my parts washer nozzle directly into the case. I just let it flow and then began rotating the crank, while still upside down. I didn't want all that crap settling down into the bottom of the case and bearings. Fortunately no pieces got jambed enought to bust out the case. The bearings are as smoot as silk. I bolted the OEM topend back on, and it turns as free as can be. I think I got lucky on this one, despite all the carnage!!!

 

[hamish]

Pissed and broke! oh wait thats me.........piston explosion caused by?? would luv to know

 

[blsnelling]

I'm gonna go with nuclear warhead over the grenade theory

And to think that this happened barely off idle as I blipped the throttle!

 

[Brian13]

Is that damage to the case I see? The first thing I noticed was a circlip in the crank but I think that might be due to piston explosion. Then I noticed what looked like case damage. Is it possible that the cylinder shifted when you hit the throttle causing the piston to hit the case. I have been thinking about doing that project one day and that has been one of the things that has crossed my mind a being a potential problem. Either way hope you figure it out and I am sorry to see that I would be in tears.

 

[Dan_IN_MN]

Ouch! JB weld will not help here! :jawdrop:

Sorry to see that!

 

[blsnelling]

Is that damage to the case I see? The first thing I noticed was a circlip in the crank but I think that might be due to piston explosion. Then I noticed what looked like case damage. Is it possible that the cylinder shifted when you hit the throttle causing the piston to hit the case. I have been thinking about doing that project one day and that has been one of the things that has crossed my mind a being a potential problem. Either way hope you figure it out and I am sorry to see that I would be in tears.

There was definately no interference with the case. It would be impossible for the cylinder to shift. The case is fine, only scraped up a little.

 

[PogoInTheWoods]

Not "properly tuned" for E10?

opcorn:

 

[Teddy.Scout]

There was a rotation (wooble, some sort of movement) to the piston.
I am guessing by the amount of damage to the piston, that it locked some how and with the force, loaded up and let loose. This would also explain the case damage.

But who am I to say!

 

[rattler362]

Brad i would like to tell you what broke first but i honestly don't know please if you figure it out let us know.

Mike

 

[wigglesworth]

Oh crap. That thing tossed it's cookies for sure.

Are you sure you clearanced the case enough? Maybe the piston hit? It was the 54mm kit, right?

 

[blsnelling]

There is no case damage that I'm aware of. Only gouges from the broken pieces of piston down in the rotating assembly.

 

[mark360T]

sorry to hear that happened to you Brad, maybe it was a dud

 

[wigglesworth]

There is no case damage that I'm aware of. Only gouges from the broken pieces of piston down in the rotating assembly.

Well if it didnt hit the case....metallurgy failure? Maybe it tossed the clip? How does that clip that was out seat in what's left of the pin boss?

 

[swamprat46]

Yikes! I didn't realize they allowed X-rated pics on this site! Sorry for your loss, maybe just a little tight and got hot idling, just happened to get tight when you blipped it?????

John

 

[polkat]

that is some carnage WOW, no bodily injuries I hope. my vote nitrous explosion, it would sound cool, maybe not. this is intresting

 

[blsnelling]

Oh crap. That thing tossed it's cookies for sure.

Are you sure you clearanced the case enough? Maybe the piston hit? It was the 54mm kit, right?

Yes, 54mm. It wasn't even close to the case. I relieved the case to the diameter of the BB gasket, which is considerably larger than the bar. I also went far deeper than needed. The piston skirt only drops maybe .020" below the deck of the case. I think what you guys are thinking is case damage, may be where I ground on the case for clearance. I just double checked and it definately did not interfere with the case at all.