Anybody have any ideas what caused this piston failure?

[blsnelling]

No radial play is acceptable in the rod bearing. You well be able to rock it left and right, as well as sliding it left an right. If you have radial play, you need a new crank.

 

[nmurph]

...as I do value the input from all the forum experts.

Seriously??? Experts?? Surely you jest.

I would guess piston slap if it wasn't done with an impact. It could also be that a bearing went south and let the skirt bang into the case.

 

[67L36Driver]

Just plain overspeed I suppose.

Pioneer P-21. WOT no load.

 

[excess650]

The piston on the Pioneer, whats left of it, appears clean.

 

[Byrdmando]

No radial play is acceptable in the rod bearing. You well be able to rock it left and right, as well as sliding it left an right. If you have radial play, you need a new crank.

Excuse my ignorance....but what is "radial play"? I can slide the connecting rod left and right to where I can see the ends of the bearings. Does that sound ok?

 

[Dan_IN_MN]

Excuse my ignorance....but what is "radial play"? I can slide the connecting rod left and right to where I can see the ends of the bearings. Does that sound ok?

Without the crank main bearings turning (put crank on TDC), you shouldn't get any up and down movement of the big end or wrist pin bearings.

 

[rob066]

It looks like the metal eating monster took a bite out of it.

 

[albert]

Usually a piston skirt will break like that when piston to cylinder clearance becomes excessive. The first sign of it is, with a keen ear, you can hear "piston slap". Simply "cleaning up" the cylinder and installing a new "meteor" is likely to have the same result. The clearance should be checked with a micrometer and bore gauge. If those tools aren't available, head to the local machine shop and they can do it for you. The other option is to replace the cylinder along with the piston.

It's not a iron bore, it's chrome or nikasil plated. The plating is only a thou or so thick and it's hard as hell.meaning it can't wear enough to cause slap. It's the piston that wears, usually from poor air filtration.

 

[bonden]

This piston looks like to have the same damage the Stihl cut off saws i rebuild , it usually have to do with dirty air filter and poor maintenance,the concrete dust realy eat pistons.

 

[lone wolf]

Two Stroke Piston Diagnosis

Check out picture 6. Anyone that rode dirt bikes with his friends and put lots of hours on a piston know this is caused by slapping then cracking and finally letting go. Ask the OP if he air gunned it over and cracked it. If he did not how do you think it happened? I will bet on it.

 

[Byrdmando]

Two Stroke Piston Diagnosis

Check out picture 6. Anyone that rode dirt bikes with his friends and put lots of hours on a piston know this is caused by slapping then cracking and finally letting go. Ask the OP if he air gunned it over and cracked it. If he did not how do you think it happened? I will bet on it.

I most certainly did not air gun it. I do not even own an air gun. I was simply sawing fire wood and was in a 20in piece of white oak and the saw "sounded a little funny" and then just stopped working. I pulled it out to try to start it again and the pull cord would not budge. I then tried to turn the flywheel and realized it was totally locked up. That is what brought me here and here I am.

Now, there might be some degree of truth to the idea that I was not particularly diligent on the maintenance side but much of that can be attributed to ignorance of procedure. This forum has helped a great deal in that regard and I will certainly not repeat past mistakes.

 

[lone wolf]

I have one in my shop from a MS440 same thing happened if you need to see pics I can get some. That simply wore out.

 

[Fish]

I most certainly did not air gun it. I do not even own an air gun. I was simply sawing fire wood and was in a 20in piece of white oak and the saw "sounded a little funny" and then just stopped working. I pulled it out to try to start it again and the pull cord would not budge. I then tried to turn the flywheel and realized it was totally locked up. That is what brought me here and here I am.

Now, there might be some degree of truth to the idea that I was not particularly diligent on the maintenance side but much of that can be attributed to ignorance of procedure. This forum has helped a great deal in that regard and I will certainly not repeat past mistakes.

Well we still need some pics...

Did you even tell us what saw this was out of?

Also, any other details at all, no matter how obscure?

Without pics and details, I won't play anymore......

How many cylinder bolts?

Were they loose?

Any worn out bearings?

Put up some more details/info, or else I will write this one off.

 

[Fish]

OK, searching your other threads, i see it is a 55. Sounds like you removed the cylinder first, viewing all of your posts, then were in a quandry about the clutch and flywheel.

Show us pics of the other side of the piston, the rest of the piston parts, and the details of the failure.

If that part let go during use, we should see some major carnage, show us the parts that were left over, we would see some major gashes somewhere!!!!

 

[Fish]

We are glad to help, but we need info and the truth, either/or.......

 

[A100HVA]

i'm with you,fish!!!!

 

[Fish]

Naw, I just smell something.....

 

[Fish]

Come on now...........

 

[lone wolf]

View attachment 267518

 

[lone wolf]