Having trouble with stihl 261c rebuild.

[stihlproincky]

Hi guys, I have a 261 on the table for a new piston, put it together this evening and tried to start it here's where the problem is. When it tries to start it "pops"
What I mean by pops it's like super high compression, so high that it forces air out the muffler so fast that it makes a pop. It won't start, everything seems smooth with the p/c.
This saw was blown up, I did have to cleanup the cylinder wall below the exhaust port due to aluminum transfer.
Any ideas what the problem is?

 

[Woodwackr]

Hi guys, I have a 261 on the table for a new piston, put it together this evening and tried to start it here's where the problem is. When it tries to start it "pops"
What I mean by pops it's like super high compression, so high that it forces air out the muffler so fast that it makes a pop. It won't start, everything seems smooth with the p/c.
This saw was blown up, I did have to cleanup the cylinder wall below the exhaust port due to aluminum transfer.
Any ideas what the problem is?

Did you get parts based on the sn or…?
Did you check for other possible damage?

 

[stihlproincky]

I did not, the dealer didn't have it on record and 1 digit on the saw was rubbed off. Is their numerous options for the piston? Everything else checked out on the saw as far as my knowledge of saws can recognize. As I said it turns over with ease, no catches. Feels like normal compression.

 

[Woodwackr]

I did not, the dealer didn't have it on record and 1 digit on the saw was rubbed off. Is their numerous options for the piston? Everything else checked out on the saw as far as my knowledge of saws can recognize. As I said it turns over with ease, no catches. Feels like normal compression.

There are several versions. Did you compare the new with the old?

 

[stihlproincky]

Pull it 2-3 times before it does this. Could this be due to lack of compression due to the cylinder being out of round?

 

[stihlproincky]

There are several versions. Did you compare the new with the old?

I didn't, but I'll pull it apart tomorrow and see. Rookie mistake I know.

 

[stihlproincky]

Dealer did ask how many fins the cylinder had, we ordered the piston based on that.

 

[Woodwackr]

Dealer did ask how many fins the cylinder had, we ordered the piston based on that.

There are two distinctly different cylinders…one straight, one slant.
Got the piston in the right direction?

 

[Woodwackr]

Mtronic or not?

 

[stihlproincky]

Yes m-tronic, yes the piston in the right way, arrow towards the exhaust port.

 

[Woodwackr]

Yes m-tronic, yes the piston in the right way, arrow towards the exhaust port.

What color solenoid?
Did you rebuild the carb?

 

[stihlproincky]

Here's the cylinder before and after I cleaned it up.

And the piston that was toasted.

 

[stihlproincky]

What color solenoid?
Did you rebuild the carb?

No I didn't rebuild the carb, I'll have to look at the solenoid tomorrow.

 

[stihlproincky]

Working on this saw for the neighbor, he ain't got a lot of money so I'm on a budget. Just rebuilt 2 of mine and haven't had a single issue. This has me stumped.

 

[stihlproincky]

---

It's a 2020 saw, FYI.

 

[drf256]

Did you figure out why the saw failed initially?

It’s an M-Tronic saw that failed. Unless you are 100% it was straight gassed, there is another problem with the saw that caused it to fail initially.

You’re lucky it didn’t run, or you risked ruining the new piston too.

I’d check the entire fuel system. There’s a rebuild kit that includes a solenoid, new filter and (I think) a fuel line. I think there are 2 fuel lines in that saw. One in the tank and one from the body of the saw to the carb. I’d pressure check what you have there.

There should be only one piston for that saw, whether it’s a V1 (traditional fin) or V2 (slanted smaller fins) saw.

 

[bogieboy]

Sounds like a failed mtronic solenoid, along with what looks like an overheat sieze from a dull chain.... mtronic noid will make it pop but not run...

Also check flywheel timing hasnt shifted....

All that assuming you did proper case vac/pressure test to verify crank seals and bottom end are tight, and no tears in the intake boot....

 

[stihlproincky]

Sounds like a failed mtronic solenoid, along with what looks like an overheat sieze from a dull chain.... mtronic noid will make it pop but not run...

Also check flywheel timing hasnt shifted....

All that assuming you did proper case vac/pressure test to verify crank seals and bottom end are tight, and no tears in the intake boot....

Buddy, you nailed it! this is a neighbors saw he he abuses it! Hella dull chain. Intake boot checked out, flywheel timing checked out, I ain't got a vac/pressure tester, but I looked over everything and it checked out. Thanks for the input

 

[stihlproincky]

Did you figure out why the saw failed initially?

It’s an M-Tronic saw that failed. Unless you are 100% it was straight gassed, there is another problem with the saw that caused it to fail initially.

You’re lucky it didn’t run, or you risked ruining the new piston too.

I’d check the entire fuel system. There’s a rebuild kit that includes a solenoid, new filter and (I think) a fuel line. I think there are 2 fuel lines in that saw. One in the tank and one from the body of the saw to the carb. I’d pressure check what you have there.

There should be only one piston for that saw, whether it’s a V1 (traditional fin) or V2 (slanted smaller fins) saw.

I could not, it's a neighbors saw a he won't say for sure, but he saying no straight gas.

 

[stihlproincky]

Did you figure out why the saw failed initially?

It’s an M-Tronic saw that failed. Unless you are 100% it was straight gassed, there is another problem with the saw that caused it to fail initially.

You’re lucky it didn’t run, or you risked ruining the new piston too.

I’d check the entire fuel system. There’s a rebuild kit that includes a solenoid, new filter and (I think) a fuel line. I think there are 2 fuel lines in that saw. One in the tank and one from the body of the saw to the carb. I’d pressure check what you have there.

There should be only one piston for that saw, whether it’s a V1 (traditional fin) or V2 (slanted smaller fins) saw.

Is that kit from stihl or aftermarket?