Pondering the fate of my Stihl 025

[torch]

I'm new to this site, google brought me here.

I have a Stihl 025 that I purchased new in the mid-90s (94? 95?). It has had a fairly easy life, generally cutting fallen trees obstructing the driveway or clearing a spot in the bush. Let's call it 10 hours a year for 20 years. Now that my sons have grown, they occasionally borrow it for their own use. #2 son recently returned it reporting that it wouldn't idle or restart when hot. While I have little experience with chain saw motors, I have extensive experience working on outboards and motorcycles, so I thought I'd have a look.

He'd been fiddling with the mixture screws trying to get it to run. It took a shot of quick-start, but I did get it running at full throttle. It was spitting fuel back out of the intake. I found he had the high speed screw backed out 6 turns! And the low speed 2.5 turns. I reset the high speed to 2.5 turns, cleaned the plug and managed to get it started again after many pulls. Much less fuel was spitting back out, but again, it wouldn't idle.

I checked the spark with a gap-type tester and found it very weak -- the gap had to be nearly closed and the motor pulled over very hard to get any spark at all. I pulled the side cover and disconnected the kill switch wire to ensure it was not shorted out. I compared the spark to my Stihl MS 290, which has a strong spark that easily jumps a 3/16" gap with a moderate pull. Secondary coil resistance is 1.1Kohms, which seems reasonable and confirms good contact between the sparkplug boot and wire. Primary coil resistance seems rather high at about 5.4Kohms. From what I can tell, the coil and ignition module are integral, so perhaps that makes it impossible to measure the true primary resistance? Anyway, everything points to a new coil required.

I also decided to check the compression, and found it to be very low. I'm getting about 40psi. Now, my compression tester is a rubber-hose type, which in my experience tend to read a bit low on small-displacement cylinders, so I'm not sure that should be taken as gospel just yet. However, the MS 290 reads over 100 and a few drops of oil in the cylinder brings the compression up dramatically, close to 100.

Peering in the sparkplug hole and the exhaust port (broke both studs getting that off! :msp_mad The cylinder walls don't look too bad -- some vertical striations but no visible gouges or grooves. Same with what part of the piston is visible through the exhaust port -- definitely vertical marks, but no grooving or galling as far as I can tell. So my working hypothesis at this point is stuck rings.

So I need at least a coil and probably at least a piston/ring kit. And some gaskets. (And two studs, but I can make those.) From what I've read, Canadian Stihl dealers want $100 for the coil and I'm sure they'll want as much again for a piston kit. That's about half the price of a brand-new saw! On-line prices are less than half of that even with shipping but I have two concerns: quality and accuracy. The coil in my saw is white, all the ones I see online are black. Did Stihl make a change mid-production? Or are these cheap Chinese knock-offs that will last all of 15 minutes?

As for the piston kit, I gather that Stihl made a change from 42 to 42.5mm at some point. I would guess that my saw is the 42mm version (haven't disassembled things far enough to measure yet), and have seen some references here to people "upgrading" to the larger size. That makes some sense if the dis-assembly shows the cylinder is worse than it looks, but is it worthwhile to do otherwise? And again, I'm pretty sure most of what I can find online is aftermarket. Are there some sources of quality components (preferably that will ship to Canada, but I have a buddy in the US who can forward stuff if necessary)?

Any comments or suggestions are gratefully received.

 

[w8ye]

The 42.5mm didn't come out until around 2000. The 42.5's are 4 port and the same as the MS250'S.

 

[w8ye]

Seems like I remember a after market MS 250 short block that was pretty good being presented on AS recently?

 

[NewToStihl]

Welcome to AS! Very nice post – thorough and well written. Sufficient information goes a long way!

You’ll get a lot of help here, but I’ve worked on several 025’s, so here’s your third of many responses…

I’ve seen a coil go bad on an 025 where the symptom was a cease in operation when hot. Starts and runs just fine when cooled off, but either quits when it gets hot, or won’t restart after being stopped. Now, that said, I’ve never seen a white coil? All of the 025’s I’ve worked on have had black coils. They were in fact OEM coils, so perhaps there were 2 different kinds and/or different types in the north?

I think both the H and L screws on an 025 should only be backed out one full turn? Where did you get the 2.5 turn info? That might explain the idle and run issues.

Compression should be much higher than 40 psi. Ideally ou’ll want 140 or higher. I think you might have an issue with your tester as a saw with only 40 psi wouldn’t start or run at all from my experience. With some light scoring (the vertical lines you reference) you might have lower compression, but it has to be higher than 40 psi if it runs at all. Your MS290 is likely higher than 100 psi as well. Do you have access to another compression tester for comparison?

With regards to piston kits . . . that’s a heavily debated topic. Some folks will tell you OEM all the way. Others will tell you Meteor kits are just as good as OEM at a lower cost. Some will tell you any Chinese knock-off is acceptable as long as you put good quality rings on it (e.g. Caber) instead of the ones that come with it. I’ve done all of these on 025’s. A no-name Chinese cheapy worked okay, but didn’t make the compression I would like to see (135 after break-in), and I can’t speak for what they’re like after years of service – I used one for a buddies saw who does part-time tree work and it survived one season very well so far. Pick your poison on that – it depends very heavily on how much you want to invest into your saw.

I believe you can mount the newer (MS250 - 42.5mm) cylinder right onto an 025. If you don’t need a new cylinder then don’t bother though. If you do need a whole new top end it’s probably a good idea. Good luck!

 

[deezlfan]

Hello, welcome.

Sounds like the mixture screws are still too far out and you may have too much fuel washing the cylinder. There are many Stihl experts here and I will defer to them but look for the simple things First!

 

[Saw Dr.]

You need to put up some pics. Coils can and do go bad on those saws. You will probably also need crank seals, a carb kit, and a new fuel line. You may want to make sure your coil air gap is set properly before you go any further, and also pull the plug boot off to make sure there is not corrosion around the spring inside there. Might be as simple as nipping the wire back a few mm, and putting back together. Set the gap with a business card to get it close, and try spark without any plug boot on and kill wire disconnected AT THE COIL. If the spark is still weak/none, then you need a new coil. If the piston is not scored, check your compression tester. You may also be surprised to find that the carb for that saw is around $30 new, so rebuilding the old one may not be worth it.

 

[pioneerguy600]

Your cylinder will most likely clean up good enough to put a new Meteor piston in it. The Meteor piston and rings are very good quality and fit. Use the OEM wrist pin and OEM clips, used ones if in good condition or get new ones from a dealer. Check the bearings closely, they are usually good but every case is different, install new seals anyway, they are cheap and worth the money to install now. The coil should be black, a good used one won`t cost no wheres as much as a new one, they really are not prone to going bad on the 025 unless they are run too hard and overheated often. You most likely can rebuild that saw with good parts for under $150. and have a good running saw that should give good service for many years.

 

[torch]

Welcome to AS! Very nice post – thorough and well written. Sufficient information goes a long way!

My first time to this forum. I've helped many people on other mechanical-related websites over the years, and realize the quality of the help someone can provide is directly proportional to the quality of information provided.

Now, that said, I’ve never seen a white coil? All of the 025’s I’ve worked on have had black coils. They were in fact OEM coils, so perhaps there were 2 different kinds and/or different types in the north?

Well, I am in the Great White North Nice to know that black ones are OK too, 'cause that's all I've found on-line and since I posted the first message, I've talked to the Stihl dealer (stealer?). Coil: $125. Piston kit: $90. New saw: $350. Ain't gonna happen.

I think both the H and L screws on an 025 should only be backed out one full turn? Where did you get the 2.5 turn info? That might explain the idle and run issues.

I was pretty sure 2.5 turns was probably still rich, but better rich than lean, as a starting point right? By the time I was done fiddling, I think I had the high speed in to around 1 turn or so. I never did get to adjust the low speed, since it wouldn't idle. I suspect the rich mix may actually have been helping seal things and boost compression (similar to a drop of oil).

I think you might have an issue with your tester as a saw with only 40 psi wouldn’t start or run at all from my experience. With some light scoring (the vertical lines you reference) you might have lower compression, but it has to be higher than 40 psi if it runs at all. Your MS290 is likely higher than 100 psi as well. Do you have access to another compression tester for comparison?

Yes, the rubber hose testers are fine for large cylinders and great for hands-free operations, but the extra volume and expandability are not conducive to accuracy for small engines. That's why I was comparing the results to the 290 -- yes it's slightly larger, but not significantly for this purpose. It's much newer, and idles fine, so as a comparative benchmark I think it reflects something close to what the 025 should be on that particular gauge.

I have a rubber-cone seal one, but I didn't have a helper to hold it firmly in place while I pulled the saw over. My other rubber-hose style compression tester is currently disasssembled -- I was using the hose as an airline adapter to hold the valves up in a MC engine while I changed valve seals.

You need to put up some pics.

]

What would you like pics of? The white coil?

Coils can and do go bad on those saws. You will probably also need crank seals, a carb kit, and a new fuel line. You may want to make sure your coil air gap is set properly before you go any further, and also pull the plug boot off to make sure there is not corrosion around the spring inside there. Might be as simple as nipping the wire back a few mm, and putting back together. Set the gap with a business card to get it close, and try spark without any plug boot on and kill wire disconnected AT THE COIL. If the spark is still weak/none, then you need a new coil. If the piston is not scored, check your compression tester. You may also be surprised to find that the carb for that saw is around $30 new, so rebuilding the old one may not be worth it.

All good advice.

Carb is clean as a whistle inside. I blew out all the passages, just in case. No damage to the needles under 5x magnification. But if I still have trouble once I get the compression and spark sorted, then a new carb might be in order -- I didn't remove the welch plug. The fuel lines seem fine -- smooth, flexible, no obvious deterioration. I don't think the crank seals are leaking significantly as that usually leads to an oily residue flung off around the magneto -- at least with outboards and snowmobiles. I didn't see that sort of pattern underneath the cover. (Of course, with my luck, the existing seals will be the next thing to fail...)

Spark plug boot is completely corrosion-free, with good contact between the wire inside and the spring (I took the boot off and metered everything. Then metered again after reassembly.) The testing I did last night was with the kill wire disconnected at the coil. I've got no spark at all now -- I've even tried taking the cover back off now spinning the crank with a drill. Air gap is set to 0.010" (on the magnet side -- the counter weight side has greater clearance for some reason).

 

[Stihlofadeal64]

Your cylinder will most likely clean up good enough to put a new Meteor piston in it. The Meteor piston and rings are very good quality and fit. Use the OEM wrist pin and OEM clips, used ones if in good condition or get new ones from a dealer. Check the bearings closely, they are usually good but every case is different, install new seals anyway, they are cheap and worth the money to install now. The coil should be black, a good used one won`t cost no wheres as much as a new one, they really are not prone to going bad on the 025 unless they are run too hard and overheated often. You most likely can rebuild that saw with good parts for under $150. and have a good running saw that should give good service for many years.

+1 for me here. The 025 is a keeper saw. If it has been virtually an "around the house" saw it is worth fixing. With your experience on outboards and bikes this should be relatively easy. There are plenty of great folks here that can answer questions and walk you through most problems that you encounter. I've used aftermarket oil seals for these saws with great success. If your cylinder cleans up (or is not scored at all) a nice meteor piston with caber rings will bring this saw back to life. As for the carb, if it is the 3 screw WT215 made by Walbro the rebuild kits here are $8.00 and they are quite easy to go through. That being said, I've been through many of them and most all of them have cleaned up and worked fine. If I tore the clam shell engine down (since it is 20yrs old). I'd automatically invest in a new fuel line, and impulse line (fuel line here $8.00, impulse around $6.00 and that's genuine Stihl!). Sounds like a great project if you're interested in working on the saw -- take your time, post some pictures if you have further questions.
Happy Sawing!

 

[torch]

It appears that Meteor only makes the 42.5mm version of the piston.

This fellow: hlsproparts.com has the 42mm version in a "Quality aftermarket piston assembly" of unknown vintage. But, he lists Caber rings separately in the 42mm size (as well as the 42.5mm). Caber doesn't list any on their website in 42mm, but I suppose it's possible he has found a ring for a different brand that will fit. The joker in that deck is he lists it as 42 x 1.5mm, and everything else I read suggests this saw uses 1.2mm wide rings. Typo?

For "brand name" piston kits in the 42mm size, I've found something called "VEC" -- made in India. India is the new China. At least the Chinese have had time to learn. Oddly enough, the same retailer (northwoodsaw.com) sells a coil by VEC, but I don't know if it's the same company. VEC ignitions seems to be in Serbia. I didn't know they made anything in Serbia -- I thought they were still bombed back into the stone age.

I also found a brand called "Episan", sold by an eBay vendor in Greece but made in Turkey. Oddly enough, I found a thread on this board from two or three years ago indicating that northwoodsaw used to sell these too. Some other threads on this board indicate the quality is generally acceptable.

Any thoughts on the above alternatives?

 

[pioneerguy600]

The Episan pistons are generally good quality, I have used two different model ones I got from the Greek.

 

[H 2 H]

Good advice above

I would like to see a pic of the coil area; I just did one and the coil area was coated with chips/saw dust/oil and the the area on the coil and flywheel was a mess I took some scotch brite to both and boy did that help out with the spark

 

[Mtthwvn]

.... I took some scotch brite to both and boy did that help out with the spark

I've done this quite a few times on mowers that have been left out in the weather. Does the trick on a lot of them

Matt

 

[torch]

Ok, if I did this right, there should be a photo of the area, complete with white coil:

View attachment 292172

Hey, it worked! Note that there was more dust and dirt in there, but I had already blown it out with compressed air.

 

[Stihlofadeal64]

Looks like you're rolling! You even posted a picture. Congratulations, quite a feat for a guy totally new to the site. Hope you get all the issues resolved with your saw.

 

[7sleeper]

As usual fantastic info here on this site!

For me your description of the problem sounds like a typical carb problem and Stihl has on all saws as far as I know H/L 1/1. So that would be for me the main culprit.

Another thing I would consider is definately cleaning the carb in a ultrasound cleaner. I have the small el cheapo model and just let it run 3x and change the water after each use. Put in a carb kit first and see how it works then. Carbs don't like newer gas formulas that much but you probably already knew that.

Second before ordering a new piston, I would excactly measure the old one. You might only need a new ring and everything would be good to go again.

Third I would think seriously about replacing stuff like crank seals, etc. if you already have your saw on your operating table.

Good luck!

7

 

[old-cat]

If you order from the Greece dealer your wait will be LONGGGGGG. I got an Episan piston from him and I have no complaints except the wait.

 

[H 2 H]

Ok, if I did this right, there should be a photo of the area, complete with white coil:

View attachment 292172

Hey, it worked! Note that there was more dust and dirt in there, but I had already blown it out with compressed air.

Sweet pull the coil off and touch up both the coil contacts and flywheel contact with some scotch brite and see what happens. When you replace the coil put a business carb between the two than tighten it up

On my MS 250's I've changed the carbs to WT 215 made by Walbro and they run a little better than Zama carbs IMO

 

[Stihlofadeal64]

Sweet pull the coil off and touch up both the coil contacts and flywheel contact with some scotch brite and see what happens. When you replace the coil put a business carb between the two than tighten it up

On my MS 250's I've changed the carbs to WT 215 made by Walbro and they run a little better than Zama carbs IMO

I'd take (1) WT215 before I would look sideways at a Zama. Just my experience with them. Besides that Zama was bought out by Stihl. Anyone who buys Stihl parts knows that they jack up the price to an unreasonable level. Just checked on a carb from Stihl ($110.00). I told the parts guy....nope not going that route.

 

[torch]

I wrote to hlsupply.com and asked what brand of piston they were offering for this saw. Their reply:

"We have a GOLF brand and another brand in a plain box made in India."

If the name sounds familiar, it was featured in this review in another thread on this website here:

http://www.arboristsite.com/chainsaw/227049.htm

I don't think that looks like something I want to put in my saw.