(resolved) Stihl 025 won't turn over with spark plug in

[mzimmers]

Hi all -

I was given a Stihl 025 a few years ago by some aging neighbors. First thing I did was take it to a Stihl dealer for a look-at and fix-up. Since then it's run fine, though occasionally hard to start. This last weekend, though, it went from hard to impossible. Looking at some tips, I verified the pull mechanism was good, then removed the spark plug. With plug out, it's super easy and smooth. Next step was the muffler. I removed it and looked inside -- it looked great.

I've heard that some 025s featured a compression relief valve; sadly, mine doesn't appear to be such a model. Any suggestions for why/how this might have happened, and more importantly, what to do?

Thank you.

mz

 

[Ronie]

Do you mean that It's phsysically hard to pull over, like the compression has increased? When you looked at the cylinder, did it have a lot of carbon build up on top of the piston? When you looked at the piston, how did the side of it look? Did you check the muffler screen to see if it was clogged up?

 

[mzimmers]

Hi Ronie -

Yes, that's it - with the spark plug installed, it's essentially impossible to pull the cord. This was true with the muffler off, so I don't think the problem is on the exhaust side. The piston and cylinder looked OK (as far as I could tell); like I said, with the plug out, it's very smooth.

 

[Bob Hedgecutter]

Hydraulic locking would be my first guess off the evidence provided thus far.

 

[mzimmers]

Hi Bob - so, what is the remedy for this?

 

[Bob Hedgecutter]

Hi Bob - so, what is the remedy for this?

First, ascertain that is your problem- is the saw flooding, when you take the plug out is the plug really wet? Turn the saw upside down with the plug out, does a lot of fuel mix come out the plug hole?
If the combustion chamber is full of fluid- it will not compress like fuel vapour and air- so will stop the rope. Could also be below the piston and the crankcase is full of crud and fuel mix, plug out, saw upside down, pull the rope over- is there fluids dripping out the open plug hole?
Could be ignition way out of timing- sheared flywheel key, could be fluid locking, could be something broken catching at one point in the pistons travel (though this should show with the plug out as well as in), could be failed top end conrod bearings, could be unnoticed damage to the starter or the starter rope.

But if you have a large amount of fuel entering the combustion chamber and the saw is not igniting it, it will flood to the point it locks the saw up. Needle valve in the carb could be stuck, or worn out.
I do not have experience with your funny fuel over there- no ethanol over here- but I hear it does funny things to carb parts after a while.
The 025/250 series of saws are known for being not so easily started from new- if you are missing the full choke pop from cold starting and continue to pull the cord several times on full choke- it could just be simple flooding.

 

[mzimmers]

When I remove the plug, it looks fine (not wet).
No fuel mix comes from the plug hole when I turn the saw over.
And I'm using ethanol-free fuel for just the reasons you cited.

 

[Ronie]

I wish I could think of something that would help you out. If it was mine acting the way yours is, I'd pull the cylinder and have a look. You could ask over on opeforum.com, a lot of smart guys over there.

 

[mzimmers]

What I don't understand is, if it's hydraulic locking, why doesn't removing the spark plug and pulling the cord several times fix this? Shouldn't turning the engine over a few times clear any areas that might be locked?

 

[Ronie]

What I don't understand is, if it's hydraulic locking, why doesn't removing the spark plug and pulling the cord several times fix this? Shouldn't turning the engine over a few times clear any areas that might be locked?

If you don't have fuel comming out the exhaust and your plug is dry, I say that it not hydraulic locking.

 

[Ronie]

It could be your starter binding up with the plug in and there isn't enough pressure on it to bind with the plug out. Have you tried to turn it over by hand with the starter off?

 

[Bob Hedgecutter]

If you don't have fuel comming out the exhaust and your plug is dry, I say that it not hydraulic locking.

Which leads us back to all the other possibilities I listed.
Now let the fun begin as we try to crystal ball gaze the correct scenario.

 

[Ronie]

Which leads us back to all the other possibilities I listed.
Now let the fun begin as we try to crystal ball gaze the correct scenario.

Hard to diagnose some problems over the net. lol
It's a lot easier when you got it in your hand.

 

[Ronie]

If it's not a starter problem, I'm out of ideas.

 

[mzimmers]

Well...I got it working (though I'm not sure how). I looked at Bob's suggestions a little more closely, and I pulled the cord with the saw *upside down* as he suggested. Before this, I was doing the same thing but with the saw on end, not upside down.

Still nothing came out of the plug hole, but I was able to pull the cord, and after a few tried, it started up.

Thanks for all the suggestions.

 

[Bob Hedgecutter]

Well...I got it working (though I'm not sure how). I looked at Bob's suggestions a little more closely, and I pulled the cord with the saw *upside down* as he suggested. Before this, I was doing the same thing but with the saw on end, not upside down.

Still nothing came out of the plug hole, but I was able to pull the cord, and after a few tried, it started up.

Thanks for all the suggestions.

Okay, so from that we can assume the crankcase might have been full of fluids- did it smoke a lot more than usual on start up?
It could be that vacuum is still pulling fuel into the chamber after the saw is shut down and put away for a period of time, seeping past the rings as the saw cools and filling the crankcase.
How long had it been sitting before you went to start it, when the problem arose?
The original post lends a bit of a hint with the saw being hard to start sometimes- before it refused to start.

EDIT: if there was nothing in the way of fluids came out the plug hole upside down....... then maybe you are okay in the flooding respect, but have broken ring/rings or bits of bearing floating about and turning the saw upside down, jarring on the starter rope, may have dislodged the ring from transfer port, or bearing piece and allowed the saw to start.
If that is the case- something will explode soon enough and confirm diagnosis.

 

[mzimmers]

Hi Bob -

Honestly, I didn't run it long enough to answer the question about smoke. I just did the upside-down thing, then put it back together and got it to start. Ran for like 2 seconds, then died (because it was still cold).

It hadn't been sitting a real long time - maybe a few weeks or so.

 

[RedneckChainsawRepair]

Check around your flywheel to make sure something isnt attaching to the magnets. When upside down might have helped move it around. Just in case.
I have had saws come in locked up and something like this is all it was.

 

[Kletus]

I have 2 Stihl 038 magnums that did the same thing. Pulled through easy with the spark plug removed but locked up when I reinstalled the plug. Probably would have damaged the starter mechanism or broke the rope if I had forced it. How I remedied it was to get the piston up close to TDC and rinse the cylinder out with straight gas, dump it out and pull it through a few times. I was using a 40:1 Echo oil. I reduced it to a 50:1 and never had tha problem again. Evidently some of the Stihl engines have a super high compression ratio and wont tolerate rich oil mixtures.