026 Piston Top

[WoodTick007]

I tore down an 026 and the attached photo shows the top of the piston. Can anyone tell me what caused the wear on the top edge of the of the piston? I would like to know before I replace it with a new cylinder assembly. Please see the atached file.

 

[jokers]

Hey WoodTick, is that a domed piston? I`ve only seen flat tops come from the factory in the 026, maybe someone else knows better however. I`ve never seen that particular stamping/marking that I can recall either. Is it possible that piston isn`t OEM or even for the 026?

I assume that the marks you are referring too are what appears to be a band on the left side of the piston as viewed. Looks like the piston has made contact with the cylinder head. Is there any other damage to the piston? Was there a base gasket in place when you tore it down? How about the bearings, are they good?

I`m probably out of my mind here but those are my first thoughts.

Russ

 

[WoodTick007]

Yes Russ it is an impact ring on the top side of the piston. No, there was not a gasket on base of the jug when removed. I don't if it is an oem piston. I never considered that it was caused due to the lack of a gasket. I removed the jug to replace the rings. The bearings on the saw seem fine.

 

[HUSKYMAN]

Why did you tear the saw down in the first place? Knocking? no compression?

 

[WoodTick007]

Lower compression caused by what seemed to be a build up of carbon in the ring grooves. The saw still ran ok..... it just had reduced compression.

 

[bwalker]

It looks like some sort of debri was banging up and down in the chamber. It is not contacting the head as the area the damage is in is right underneath the heads domef portion and the area of greatest clearance. The pic is poor, but it could also be detonation. Does material appear to be melted/sandblasted away?

 

[066 stihl]

Ben you are wrong. The edge of the piston.

 

[Fish]

Was it pinging?

 

[WoodTick007]

No Fish, It was not pinging. The only thing that I noticed that the compression was down. Not to the point the saw would not run. I will attach 2 more photos that are better.

Sorry about the picture quality.... I was just glad to get my Thumb out of the pic!!

 

[WoodTick007]

Another

 

[Jacob J.]

Some 026 saws actually did come with a domed piston- these were most notably the "026 Farm Boss" which had similar features as the other farm boss models, specifically the Farm Boss sticker on the sprocket cover and in the case of the 026, 028, and 038- a domed piston. However your saw looks like it was the victim of a "shake mill hop-up", removing the base gasket ( paper, 1mm ) in an effort to get more compression, which led to the crown of your piston striking the compression ring in the cylinder.

 

[bwalker]

Ben you are wrong. The edge of the piston.

Your right. I could not see what he was talking about in the first pic as I thought the damaged area was actually the ring hanging out. Its apparent from the last two pics that he has clearance issue. Maybe this is the wrong piston?

 

[bwalker]

BTW is it just me or does the center of the piston appear to have material melted away?

 

[WoodTick007]

shake mill hop-up

Why was this saw not knocking? Do you think it could have run long like this? I was wondering if it was perhaps the wrong piston or something. I bought it at a garage sale for $80. Maybe it wasn't the "deal" I thought it was ..

 

[dozerdan]

WoodTick007
I think that the piston was hitting the top of the barrel. Look up inside the barrel and you will see what the piston was hitting.
If someone removed the base gasket, there still should be plenty of clearance between the piston and the top of the barrel. Walker does this all the time without a problem.
I can only see two possibilities.
Someone milled the base off of the barrel or the bearings are loose. My guess is the bearings are loose.
Later
Dan

 

[WoodTick007]

Loose Bearings

Dan,
Would you be talking about the rod bearings at the crank? The wrist pin bearings seems fine. How can they be checked.

 

[jokers]

Hey WoodTick, I`d check all of the bearings. You can have acceptable lateral(side to side) movement of the big end bearing but you should not be able to move the rod out of perpendicular to the crank. Same sort of deal with the crank bearings but they are also thrust bearings of sorts so you shouldn`t get any lateral movement there. You will also want to rotate the crank checking for glass smooth rotation of all bearings. Without looking, the only bearing that could be a death sentence would be the big end rod bearing. I believe that the crank bearings are available

Oh BTW, I suddenly recognize that marking(S) on the piston. I told you that I`m out of my mind.

Russ

 

[SilverBlue]

Looking at the last picture it seems like there is significant damage that happened gradually so I would say that Dan is right. But wouldn’t bearings that loose fall apart or be noisy? I would be concerned about rod and possible journal damage.

 

[dozerdan]

WoodTick007
Russ explained the bearings rather well. I think you will find the larger end of the connecting rod loose on the crank.

Russ
I looked at the manufacturer's marking on top of that piston for 5 minutes. My 15 year old looked at it for about two seconds and said that a small Stihl piston.GGGGRRR
Later
Dan

 

[woodsjunkie]

I looked at the manufacturer's marking on top of that piston for 5 minutes. My 15 year old looked at it for about two seconds and said that a small Stihl piston.GGGGRRR

And to think we are letting this blind man inside are saws.LOL
Hows the 3120 coming gott’er dunn yet?