461 skirt on piston broke?

[beastmaster]

Im replacing the piston on my Stihl 461. I'm going to replace it with a pop up piston. Lucky for me the cylinder isn't scored.
But why would it break in the first place?

 

[Woodslasher]

Without pics I really can't be accurate, but if you use a saw enough the skirt will get worn down and it is possible for it to get thin enough that it will break as a side effect of the piston slap that occurs with a worn piston. Not cleaning/changing your air filter and letting particulates into the cylinder will accelerate that problem on the intake side especially.

 

[Gord404]

Check your bearings, possible something got caught between the crank and the piston.- just a thought

 

[Jasent]

Is the piston stuffer loose? Seen that before. Screws work out and piston bumps stuffer

 

[huskihl]

There’s only a few thousandths clearance between the intake skirt and the deflector flange. As soon as the piston gets a bit of wear, it hits the flange and cracks the skirt. Same thing on a 661

 

[Madmantrapper]

Are you referring to the wrist pin hole getting loose?

 

[huskihl]

Are you referring to the wrist pin hole getting loose?

No. The piston gets loose in the bore. And then hits the flange

 

[Madmantrapper]

No experience with the 461 but that seems like it would be a heck of a lot of wear.

 

[Jasent]

The flange is a piston stuffer. Peace of metal that protrudes from the crank case and up in to the piston to help push fuel air mix forward to the transfers. There is very little clearance.

 

[Yotaismygame]

I've seen some gnarly carnage when taking apart junker 461's from what Huskihl mentioned.

 

[Gord404]

Number 34 I believe is the piece in question, doing a rebuild on a 461 myself in a week or so and have rebuilt on about a year ago but one as a lean problem and the one I will be doing shortly the clutch side bearing went on it, - what happened to piece of piston that broke off and where did it end up? Check your con rod bearings closely and your crank bearings as well.

 

[huskihl]

Number 34 I believe is the piece in question, doing a rebuild on a 461 myself in a week or so and have rebuilt on about a year ago but one as a lean problem and the one I will be doing shortly the clutch side bearing went on it, - what happened to piece of piston that broke off and where did it end up? Check your con rod bearings closely and your crank bearings as well.
View attachment 914172

Yes, number 34. And the screws stick up above the base so you can’t do a gasket delete on a 461 without filing them off

 

[Jasent]

My personal 461 the screws are below flush with the case. Base gasket delete was no problem. Squish was huge till I took it down. Seen a few like that

 

[Kilo1988]

What if I broke part of that flange wer the screw goes through to hold it down seems taking away the flange isn't an option do I have to get a new one ?any help is greatly appreciated

 

[huskihl]

I’d remove the flange. Husky uses the same port arrangement without using one

 

[rmh3481]

Stihl cylinders dont have the flange on the bottom that you are used to seeing on other makers cylinders. This allows the base of the piston skirt to rock back and forth at BDC, and slap the cyl. Over time the piston skirt wears thin and then it cracks. More oil doesnt seem to make any difference. Its just part of the design.

 

[huskihl]

Stihl cylinders dont have the flange on the bottom that you are used to seeing on other makers cylinders. This allows the base of the piston skirt to rock back and forth at BDC, and slap the cyl. Over time the piston skirt wears thin and then it cracks. More oil doesnt seem to make any difference. Its just part of the design.

The piston doesn’t come out of the cylinder at bottom dead center though.

 

[K-techcowboy]

Stihl cylinders dont have the flange on the bottom that you are used to seeing on other makers cylinders. This allows the base of the piston skirt to rock back and forth at BDC, and slap the cyl. Over time the piston skirt wears thin and then it cracks. More oil doesnt seem to make any difference. Its just part of the design.

My thoughts exactly. Yea alot of that is avoided by simply letting your saw warm up. I see it alot on motorcycles as I work on them for a living. Harleys are the worst. Especially after the cylinder becomes egg shaped. Some of the older hotrod Harley and s&s motors are so bad you can blip the throttle and here it knocking on heavens door. Customers always think its a rod but nope its just good ol fashion piston slap. Thats why I try to stress the importance of warming your engine up on anything before you go beaten er up. Especially when these sport bikes are revin to 17 18000rpm in the blink of an eye. He got lucky it didn't destroy the whole engine.

 

[K-techcowboy]

Im replacing the piston on my Stihl 461. I'm going to replace it with a pop up piston. Lucky for me the cylinder isn't scored.
But why would it break in the first place?

Many factors lye beneath your question like hrs on saw, what you primarily use it for, is it bone stock, do you warm it up for at least 3 minutes before wot limb wackin and even which side it broke on intake or exhaust? Id say if your doing everything right it was either manufacturer defect or just a freak deal. I think those have limited coils if I'm not mistaken so shouldn't of bein able to over rev? You did go to shut it down in time thats certain. That piece could of been turned into a shrapnel grenade otherwise.

 

[Kilo1988]

I've read it can over heat the saw if it's removed is that just somethin that would happen if I use the saw for hours on end.