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

[Showme]

Can I still keep my 440/460 your built or do I have to sent it back? Seem's to run pretty good, but what do I know?

 

[edisto]

I don't think the transfers are near wide enough to catch a ring. Plus they were beveled after widening.

Beveled yes, but the side is pretty square.

More importantly, it doesn't matter how wide it is if the ends of the ring make their way in there. Hard to piece it together from the pics, but how far was the widened edge of the transfer port from the ring ends?

 

[Nitroman]

I wonder if you might of had a little piston slap and with the widened porting it caught a port with the piston skirt and them wam broke it. I base this on how the pin boss broke like it did. Its either that or the pin boss is what failed.

Bingo.

 

[blsnelling]

Beveled yes, but the side is pretty square.

More importantly, it doesn't matter how wide it is if the ends of the ring make their way in there. Hard to piece it together from the pics, but how far was the widened edge of the transfer port from the ring ends?

A ring end definately did not drop into the transfer port. That wasn't even close. The only thing close was the lower ring end to the edge of the intake port. Square sides don't catch rings. It's flat tops and bottoms you have to watch out for, particularly on the exhaust roof.

 

[blsnelling]

Bingo.

The only way a the piston skirt can catch in the port, is on the way down. There are no marks on the bottom of the intake port at all.

 

[Miniburbs36]

I have seen blown up dirtbikes, blown up weedwackers, blown up chainsaws, blown up car engines, Not yet have I seen something that insane.

I really feel for ya, and Really I can't believe my eyes.

 

[edisto]

A ring end definately did not drop into the transfer port. That wasn't even close. The only thing close was the lower ring end to the edge of the intake port. Square sides don't catch rings. It's flat tops and bottoms you have to watch out for, particularly on the exhaust roof.

It's the flat top and bottom that make the side square...and that's what I was referring to.

 

[stihlman32]

Sorry to see the carnage Brad! I thought mine was bad...

 

[bullittman281]

I'm no 2t expert but looking at it think fish is on the right track. Its hard to tell from the pictures but it looks like the piston casting is less that perfect on the flywheel side of the piston. I think it took a little bit of help but poor casting of too brittle of a material and it might just grenade. I'm not sure though. It looks like some bubbles or something in the piston fracture. Got a good close up of the fracture? Its not normal for pistons to get torn in half.

 

[songofthewood]

Looks like poor workmanship on the piston makers.Looks like air got into the casting of the piston.Sorry about the loss Brad.

 

[RAMROD48]

that's not that bad, its still recognizable....

this? Not so much....

So see....it could have been worse....

 

[Erick]

Looks to me like the left side transfer snagged a ring on the way down and ripped the top of the piston off above the ring land shattering the brittle ring allowing the broken ring end to expand into the intake port causing the damage to skirt on the intake side. Skirt probably didn't happen all in one stroke, the ring end snag just started the failure and the skirt got beat to death with every stroke that came after.

I can tell you one thing for sure... it was not a circlip issue, both of those clips were in when the catsasstrophy took place.

 

[blsnelling]

Well, I'm not too upset. The saw is back together and running with the OEM topend. It's no slouch with a popup piston and port work. I just wanted more. Maybe next time. How much you want to bet the intake isn't as wide next time!!!

 

[bullittman281]

DUDE! THAT'S AWESOME! The piston is sideways! At least Brads bottom end survived. Its got to be hard on rods to turn a piston sideways.

 

[bullittman281]

How 'bout a grenaded top end?

 

[blsnelling]

Looks to me like the left side transfer snagged a ring on the way down and ripped the top of the piston off above the ring land shattering the brittle ring allowing the broken ring end to expand into the intake port causing the damage to skirt on the intake side. Skirt probably didn't happen all in one stroke, the ring end snag just started the failure and the skirt got beat to death with every stroke that came after.

I can tell you one thing for sure... it was not a circlip issue, both of those clips were in when the catsasstrophy took place.

I can buy that. That's basically a combination of my theory, and TZeds. I still believe it started at the transfer side, and then progressed to the intake. This theory supports that.

 

[blsnelling]

Can you imagine what this would have looked like had I been tuning the H needle at WOT I probably wouldn't have a saw left to work on. It probably would have destroyed the crank and cases.

 

[mtngun]

Kudos for the excellent photographs, Brad. I appreciate you sharing this. I feel your pain.

The circlip is a chicken or egg question -- did the circlip pop out and jam the piston, or did the piston fracture first and let the circlip pop out ?

You mentioned that the piston seemed unusually hard to cut with a carbide burr. That could be significant. How would aluminum get that hard, though -- too much silicon ? I hope Grande Dog will weigh in on the piston question.

I'd like to ask you something -- and I'm not pointing fingers, just gathering information, so don't take it wrong -- how wide were the ports as a % of bore diameter ? As you know, the general rule of thumb for a work saw is 65%. I noticed that one or two of your recent 660 build were going up to 70% ? Again, I'm not jumping to conclusions, just curious.

 

[blsnelling]

I'd like to ask you something -- and I'm not pointing fingers, just gathering information, so don't take it wrong -- how wide were the ports as a % of bore diameter ? As you know, the general rule of thumb for a work saw is 65%. I noticed that one or two of your recent 660 build were going up to 70% ? Again, I'm not jumping to conclusions, just curious.

Fair question. You can't get the ports to 70% on most Stihls. They are far more limited than Huskys by both skirt width and ring end locations. The only way the "tractor saw" 066 got that wide was with use of a Husky 385 piston. The total width of the intake port was not a factor here. How close the ring end was to the edge may have played a part, but not necessarily. What looks to have burnt me here was a wider than stock transfer and not enough bevel on it.

BTW, these were not the BB rings. These were Caber rings. So it can't be blamed on the infamous BB rings, which I've yet to have a problem with. Why did I use Caber? "Group think" I guess. I guess I'm guilty of believing some of the hype myself sometimes.

 

[parrisw]

Yikes!