Another Stihl 025 Mystery

[Fish]

Yeah, I wouldn't have bothered with all of the pics, if I knew those chitheads were going to delete them.

 

[Wood Doctor]

Yeah, I wouldn't have bothered with all of the pics, if I knew those chitheads were going to delete them.
View attachment 51877

Fish, I just thought of something. That impulse hose line is probably OK and intact. Now that I took the saw almost apart, I see nothing wrong with the hose. The real problem is that the engine is not delivering the impulse through the hose that the carb needs. The rings may have a separation problem, but who knows what's causing the lost impulse?

I am leaning toward a top end rebuild even though the compression measures 145 psi. It's not a usual situation, but I'm starting to expect the unusual at this point. WDYT?

 

[Fish]

Yeah, I've run saws with the impulse line disconnected, and they never have resembled your problem. And I never really rely on a compression gauge for much. I only have one for the pic I put in my E-bay auction, on the rare times that I sell a whole saw.
Can you put up a pic of the piston/rings through the exhaust port? Also take a pic of the piston on the intake side.

 

[Wood Doctor]

Yeah, I've run saws with the impulse line disconnected, and they never have resembled your problem. And I never really rely on a compression gauge for much. I only have one for the pic I put in my E-bay auction, on the rare times that I sell a whole saw.
Can you put up a pic of the piston/rings through the exhaust port? Also take a pic of the piston on the intake side.

I'll do that as soon as I get it all apart. I'm committed to rebuilding it now. This saw has quite a few hours on it and nowadays you can get piston and cylinder kits for half the price of what Stihl used to want for them.

Frankly, I doubt I'll be putting a lot of time on this saw because I have others in the holster that weigh about the same and have more poser. However, I hate having anything on board that doesn't run. And, this has been a learning experience because I've never run into any patient with these symptoms before. It's weird.

 

[Stackowood]

On this saw you won't feel any impulse at the hole in the boot because the boot pulls away from the handle assy when the carb is removed, and any impulse leaks out around the boot flange. So you may have impulse even though it seems like you don't

Also you can change the impulse hose without pulling the handle... just reach in there with long needle nose pliers where the hose connects to the cylinder.

I just bought a MS250 p/c kit from HL on special for $17. Quality looks good and compression is 165!

 

[Wood Doctor]

On this saw you won't feel any impulse at the hole in the boot because the boot pulls away from the handle assy when the carb is removed, and any impulse leaks out around the boot flange. So you may have impulse even though it seems like you don't.

Also you can change the impulse hose without pulling the handle... just reach in there with long needle nose pliers where the hose connects to the cylinder.

I just bought a MS250 p/c kit from HL on special for $17. Quality looks good and compression is 165!

I actually checked the impulse hose line again after I removed the handle and shroud. I dabbed the grease right on the end of the hose and still had no impulse movement of the grease, spark plug in or out. There also is no crack or defect anywhere on the hose. This is really an unusual sequence of events.

Thanks for the tip on HL. I missed that one but got a good deal on another one that should be here by the end of the week. Meanwhile, I'll do a good clean up, check the seals, bearings, etc. This rebuild should not be much different from the 310 I upgraded to a 390 a few years back. A tree company gave it to me. That one's bearings were shot and the engine would not even turn over. It runs perfectly today.

 

[fearofpavement]

I've never had a saw where the impulse hose/system was "blocked" but I guess anything's possible.
So you're replacing the cylinder/piston without confirming there's something wrong with it? That's pretty extreme shotgunning.

 

[lwn9186]

I had one a piece of Dirko broke loose and plugged the hole. The saw had never been apart. Put vacuum to the nipple and see if it is plugged. Also would be worth checking the crank seals.

Pressure/Vac test should tell you something.

 

[Adirondackstihl]

Cylinder DOES NOT need to be removed to change the impulse hose.
And you don't need to remove the tank entirely either. I can replace one in about 20min.
Tiny pliers or forceps will be your friend.

The 025 hasn't been produced for some time now. It is overdue for rubber lines & such anyway.

 

[Wood Doctor]

I've never had a saw where the impulse hose/system was "blocked" but I guess anything's possible.
So you're replacing the cylinder/piston without confirming there's something wrong with it? That's pretty extreme shotgunning.

I've never had an impulse hose blocked either. By process of elimination, there is virtually nothing left that could be causing this failure to start.

Yes, I'm "shotgunning", but regardless, I may find it now that the saw is torn down, and with it this far down, I might as well rejuvenate a tired old horse and check the seals and bearings. If she fails after the rebuild, I'll part it out for fixing other 025's. I usually get several of those as time goes by.

 

[big t double]

no shot gunning necessary....

Vac/pressure test performed?

A 20min pressure/vac test would answer a lot of questions.

Pressure/Vac test should tell you something

 

[Wood Doctor]

At this point, I discovered a bad crank shaft oil seal on the clutch side, totally in pieces. That let in air and probably disengaged the impulse hose completely. That in turn made it impossible for the the carb to deliver any fuel mixture to the cylinder.

So, if I replace the crankshaft oil seals (might as well do both of them), I might be in the clear and this saw's engine may yet run again. Seem reasonable? WDYT?

 

[Adirondackstihl]

At this point, I discovered a bad crank shaft oil seal on the clutch side, totally in pieces. That let in air and probably disengaged the impulse hose completely. That in turn made it impossible for the the carb to deliver any fuel mixture to the cylinder.

So, if I replace the crankshaft oil seals (might as well do both of them), I might be in the clear and this saw's engine may yet run again. Seem reasonable? WDYT?

Sounds like a plan Stan

 

[Wood Doctor]

Sounds like a plan Stan

Plan and mission accomplished! I replaced both seals after tearing the saw down almost to the wire. Then I carefully reassembled everything with the new seals in place, resealing the clam shell. Compression still measured 145 psi.

Pulled the cord three or four times on choke. She fired. Switched to fast idle and two pulls later it started and ran. Adjusted carb for proper acceleration and idle. Bar oiler still works good. Saw is raring to go.

My thanks to all for the advice and assistance here. As a team, we saved a vintage Stihl 025 that may run yet another ten years. I have an 18" and a 16" bar and a pair of sharp chains for it.

 

[Stackowood]

Good work! Glad you got it running again.