Stihl 026 Leakage Test

[2tone]

There is a gasket.

 

[2tone]

One of the rings is stuck inside the groove on the intake side. Do you think the cylinder is salvagable?

 

[Okie]

You need to ask or check this:
Not sure about yours but some of the Stihls also used crankshaft bearings that had plastic bearing spacers in the bearing to keep the bearing spaced correctly and evenly around the race. Replace those type bearings with the type that have the steel spacers. When the plastic gets brittle it will break into small pieces and the rollers will slide instead of roll in the race. Saw will have strange noises and be little harder to hand crank intermittently when it first starts acting up.

 

[2tone]

You need to ask or check this:
Not sure about yours but some of the Stihls also used crankshaft bearings that had plastic bearing spacers in the bearing to keep the bearing spaced correctly and evenly around the race. Replace those type bearings with the type that have the steel spacers. When the plastic gets brittle it will break into small pieces and the rollers will slide instead of roll in the race. Saw will have strange noises and be little harder to hand crank intermittently when it first starts acting up.

I continued the tear down as I need to get the broken part of the piston out of the crankcase. The connecting rod bearing on the cranshaft looks really loose. I will post a photo a little later.

 

[2tone]

Here is a photo of the rod bearing. A lot of side to side room.

 

[drf255]

The crank main bearing spacing is normal. You shouldn’t have any up and down play on the rod, some side to side wobble is normal, but zero movemet up an down if you pull on the rod.

Jug might clean up, but you need to know what you are doing. Any proud areas of plating need to be sanded down. It’s been said that “nothing below the exhaust port roof matters” when it comes to jug salvage. Your areas above the ex roof do look fixable.

IMHO, that saw needs a full tear down, crank needs to go in a USC to vibrate any metal particles out of the main bearing, and it needs new bearings. Obviously a new piston and rings. Jug may clean up, but you could likely find a good used oem jug and slug on the TP here for under $100.

Stay away from any China junk for the rebuild.

Rebuilding these saws gets pricey. You may wanna just sell it on the TP here as is, agree that it’s done it’s job for you, and buy a new or used 261 Stihl here.

 

[lone wolf]

The crank main bearing spacing is normal. You shouldn’t have any up and down play on the rod, some side to side wobble is normal, but zero movemet up an down if you pull on the rod.

Jug might clean up, but you need to know what you are doing. Any proud areas of plating need to be sanded down. It’s been said that “nothing below the exhaust port roof matters” when it comes to jug salvage. Your areas above the ex roof do look fixable.

IMHO, that saw needs a full tear down, crank needs to go in a USC to vibrate any metal particles out of the main bearing, and it needs new bearings. Obviously a new piston and rings. Jug may clean up, but you could likely find a good used oem jug and slug on the TP here for under $100.

Stay away from any China junk for the rebuild.

Rebuilding these saws gets pricey. You may wanna just sell it on the TP here as is, agree that it’s done it’s job for you, and buy a new or used 261 Stihl here.

Plus one on no China Junk!

 

[lone wolf]

OP you need to figure out why the piston top hit if that is in fact what happened or was it a piece of flack?

 

[2tone]

Thanks for the feedback. I start the midnight shift tonight. So progress will be slow.

 

[lone wolf]

Thanks for the feedback. I start the midnight shift tonight. So progress will be slow.

slow is OK rush is worse.

 

[2tone]

No up and down play on the rod bearings. Checked piston and crank Looking at cylinder and piston for clues.
There is a piece of piston missing on the side.
Okie: The piston pin caged roller bearing has a steel cage.

 

[lone wolf]

No up and down play on the rod bearings. Checked piston and crank Looking at cylinder and top of piston.

Try to figure if it is an even looking strike on top or a random piece junk hit it.

 

[2tone]

Added photos with better details.
The scratch on cylinder top intake is me checking with a pick to see if there is material build up. Nothing came off.
Clues
Both jug bolts on exhaust side not tight at teardown.
Both jug bolts on intake side torqued tight.
Section of piston missing on intake side.
Piston is thin and cracked on intake side.
Bottom of jug on exhaust side has a wear or deformation spot.
Bottom of piston on exhaust side had wear on both sides
Top of jug on intake side has heavy contact.
Top of piston on intake side has heavy contact.
Top of jug on exhaust side has light contact.
Top of piston on exhaust has outer edge pushed up around rim.
Large washer on carb side of boot missing.

Passed the pressure and vacuum test
Upper piston ring collapsed into grove on intake side.

Time to get some rest for the night shift.

Thanks to all for input.

 

[SteveSr]

Okie: The piston pin caged roller bearing has a steel cage.

It is NOT the piston bearing... It is the main crank bearings. You may or may not be able to see them from inside the crankcase with a small inspection mirror.

 

[2tone]

Continued cleanup, tear down before work and the large washer on carb side of boot was behind the boot lip.

 

[2tone]

It is NOT the piston bearing... It is the main crank bearings. You may or may not be able to see them from inside the crankcase with a small inspection mirror.

I plan to do a full tear down.

 

[2tone]

I'm looking into why piston is hitting top of cylinder. No play in crankshaft bearings. No play in rod or piston bearings. The piston is paper thin on intake side and worn on exhaust side. The bottom of the piston is worn completely away on the intake side. The top of the exhaust side of the piston is wearing and extruding material upward. This allows the piston to rock or pivot in the bore. This allows the piston to pivot the top of the intake side upward. This allows the intake side of the piston to hit the top of the cylinder.
I am almost finished the midnight shift rotation and will start days on Saturday. In the meantime, I fabricated the parts for a case splitter out of available scrap and a friend welded them together. I need to counter sink the holes for the bottom bar studs and then I will split the case to complete the teardown. I will update afterwards.
I'm looking into why the piston wore down with relatively low hours on the saw over the years.
Up until a few years ago I ran ethanol gas in the saw. This would allow the alcohol to separate from the oil and gas mixture in both the saw tank and the 2 cycle mix container. This would allow straight alcohol to be feed into the carburetor for some short durations. I replaced the fuel and impulse lines a few times. They would turn to goo and start leaking. This would allow incorrect lean air/fuel mixture and reduced lubrication. The ethanol would allow the carburetor to crud up. The carburetor was rebuilt at the Stihl saw shop a few times. This would allow an incorrect lean air/fuel mixture with improper lubrication. The incorrect lean air/fuel mixture with improper lubrication would allow the engine to run at an increased temperature.
I ran Stihl oil in the gas oil mixture at the correct ratio.
Thanks to all for input.

 

[drf255]

Looking at the saw now, I think the piston plainly worn out. The intake skirt is the thrust area, that’s where they thin.

When the severely thin, the skirt to bore clearance becomes excessive and the pistons start to rock. Then the crown can rock into the band, and the bottom of the skirt can catch itself on the intake floor. Kinda looks like what happened to your saw. I had one in similar shape a few years back.

See if you can clean up that saw. Meteor pistons are cheap enough. If you need a good used oem piston, pm me.

 

[SteveSr]

Looking at the saw now, I think the piston plainly worn out. The intake skirt is the thrust area, that’s where they thin.

When the severely thin, the skirt to bore clearance becomes excessive and the pistons start to rock. Then the crown can rock into the band, and the bottom of the skirt can catch itself on the intake floor. Kinda looks like what happened to your saw. I had one in similar shape a few years back.

So what would cause this kind of intake skirt wear? Fines getting through the air filter? Could be possible with the older style fleece filters. Cutting in wet/cold/snow conditions where ingesting water will wash the oil off of the cylinder? Any other possibilities?

 

[drf255]

Just lots of use. Everything wears out.