2 stroke seized!

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

Ashful

Minister of Fire
Mar 7, 2012
19,908
Philadelphia
I was running my Stihl BG 86 hand-held blower the other day, when there was a sudden change in pitch, which I interpreted as the thing rapidly leaning out but could have really been anything. As quickly as I could reach my thumb to the throttle down / off switch, the thing seized.

The facts:
  1. I've owned this more than 5 years, maybe even close to 10 years.
  2. I replaced the carburetor with a non-OEM Buckbock C1M-S261B in October 2020.
  3. I've made no recent adjustments, everything was running well.
  4. I don't believe I straight-gassed it, I've never done that to any machine, and it was filled from the can which I use for 2-stroke only.
  5. I use this machine perhaps 30-45 minutes per week, except a few weekends each fall where it may see several hours per week.
  6. It had been running near full throttle (as leaf blowers do) approximately 15 - 20 minutes when it seized.

The theories, in my opinion as most likely to least likely:

  1. Something suddenly failed in the cheap replacement carburetor, after nearly 2 years' use?
  2. I accidentally forgot to put 2-stroke oil into my last fill of the can I use for 2-stroke machines? This is horrifying, as I'm running other more expensive equipment off the same fuel.
  3. My carburetor settings have been off for years, and it eventually did itself in?

The plans:
  1. Try to free the seized piston? Would still require figuring out what went wrong.
  2. Just replace the damn thing, and move on. It's only $250 new, has lived a good life, and is likely almost as expensive to repair as to replace (plug + jug + carb + wasted time). I'm also in the middle of some bigger stuff, and can't really afford the distraction, or to be without the thing until I'm free to work on it.
  3. Save it to rebuild later, to either keep as a spare or sell.
  4. Dump the 2-stroke mix I have now (dilute into 15 gallons of straight fuel), and mix up a new batch.
  5. Evaluate damage to other machines. Can I get the fuel analyzed? Should I just pull mufflers and inspect? Should I just leave well enough alone?
 
I was running my Stihl BG 86 hand-held blower the other day, when there was a sudden change in pitch, which I interpreted as the thing rapidly leaning out but could have really been anything. As quickly as I could reach my thumb to the throttle down / off switch, the thing seized.

The facts:
  1. I've owned this more than 5 years, maybe even close to 10 years.
  2. I replaced the carburetor with a non-OEM Buckbock C1M-S261B in October 2020.
  3. I've made no recent adjustments, everything was running well.
  4. I don't believe I straight-gassed it, I've never done that to any machine, and it was filled from the can which I use for 2-stroke only.
  5. I use this machine perhaps 30-45 minutes per week, except a few weekends each fall where it may see several hours per week.
  6. It had been running near full throttle (as leaf blowers do) approximately 15 - 20 minutes when it seized.

The theories, in my opinion as most likely to least likely:

  1. Something suddenly failed in the cheap replacement carburetor, after nearly 2 years' use?
  2. I accidentally forgot to put 2-stroke oil into my last fill of the can I use for 2-stroke machines? This is horrifying, as I'm running other more expensive equipment off the same fuel.
  3. My carburetor settings have been off for years, and it eventually did itself in?

The plans:
  1. Try to free the seized piston? Would still require figuring out what went wrong.
  2. Just replace the damn thing, and move on. It's only $250 new, has lived a good life, and is likely almost as expensive to repair as to replace (plug + jug + carb + wasted time). I'm also in the middle of some bigger stuff, and can't really afford the distraction, or to be without the thing until I'm free to work on it.
  3. Save it to rebuild later, to either keep as a spare or sell.
  4. Dump the 2-stroke mix I have now (dilute into 15 gallons of straight fuel), and mix up a new batch.
  5. Evaluate damage to other machines. Can I get the fuel analyzed? Should I just pull mufflers and inspect? Should I just leave well enough alone?
I'd pour some of the suspect fuel into a clear jar. Do same with straight gas in another clear jar. Feel, if there is an oily difference and color difference. I'd bet you added the oil.
Could do the same thing on white paper with two samples. They will look different.
 
  • Like
Reactions: sloeffle and Ashful
Thanks, @gzecc. I had been thinking of trying this, not sure if I’d be able to tell the difference, but you convinced me to go out to the barn and check it out. The difference is day and night, there’s definitely some oil in this gas:

EFE7D8EF-8E5E-4427-8722-16C8731AF038.jpeg

Close up:

8499FB13-B328-44B0-AFCB-CC2481F91E8D.jpeg

This doesn’t tell us the ratio isn’t too thin, eg. Stihl screwed up their 2.6oz bottle dosing or we’re just seeing residue picked up from old mix in the jug. But given the very noticeable color difference, and the fact that the thing ran at least 15 minutes before failing, and that this is not a new batch of fuel… a fuel mix problem is looking less and less likely.

That said, I’m still planning to dilute this batch back into my 15 gallons of straight gas sitting into the shed, and to mix up a fresh batch for the other machines. Cheap insurance.
 
Pull the muffler, take a peak. I’m guessing you run enough 2 strokes that you could hear it running to fast/ lean. My guess is a bearing. I don’t think running lean would seize it in a few seconds.

It’s probably not worth the time to fix unless it’s a skill you want to lear/ practice. And if it’s a bearing it’s probably a whole tear down if that’s even an option to get parts.
 
Thanks, @gzecc. I had been thinking of trying this, not sure if I’d be able to tell the difference, but you convinced me to go out to the barn and check it out. The difference is day and night, there’s definitely some oil in this gas:

View attachment 296974

Close up:

View attachment 296975

This doesn’t tell us the ratio isn’t too thin, eg. Stihl screwed up their 2.6oz bottle dosing or we’re just seeing residue picked up from old mix in the jug. But given the very noticeable color difference, and the fact that the thing ran at least 15 minutes before failing, and that this is not a new batch of fuel… a fuel mix problem is looking less and less likely.

That said, I’m still planning to dilute this batch back into my 15 gallons of straight gas sitting into the shed, and to mix up a fresh batch for the other machines. Cheap insurance.
Thats a good result.
 
Problem solved! New blower, and fresh batch of fuel for extra precaution:

4A132EE0-6A94-44BF-9EB5-44EF6F1A5DB3.jpeg

I will do a teardown autopsy on the old one, but that will have to wait for August or September. I have some other big projects on the docket ahead of this.

I agree it’s not likely to have been running lean for a long time, I meant to say that possibly something could have clogged or failed in carburetor to have caused it to rapidly lean out for just a few seconds before failure. But I think you’re bearing theory sounds more possible, now that I think about it.
 
Last edited:
You might have lost a crank seal...which makes an air leak...
 
  • Like
Reactions: JRHAWK9
Surprised that BG86 isn't a 4 mix model now...

There is a BG 86 C-E model now, for $10 more than the original BG 86, and with the same velocity and volumetric specs. Didn't take the time to look at what it was, but had assumed it was just a newer emissions variant, not 4-mix.

I bought the one original BG 86 they still had on the shelf, on the rule of thumb that a newer of the same model is rarely if ever better, and that I didn't want to waste any more time than needed on replacing it.
 
Problem solved! New blower, and fresh batch of fuel for extra precaution:

View attachment 296980

I will do a teardown autopsy on the old one, but that will have to wait for August or September. I have some other big projects on the docket ahead of this.

I agree it’s not likely to have been running lean for a long time, I meant to say that possibly something could have clogged or failed in carburetor to have caused it to rapidly lean out for just a few seconds before failure. But I think you’re bearing theory sounds more possible, now that I think about it.

How cute, do you use it to blow out your birthday candles? ;lol :p >> Just kidding.....

I have a big back-pack blower for blowing wet leaves out of flower beds, sticks, dog crap and peeling moss off the "lawn" and blowing it all into the woods past the "weed line" :) It was the largest one out back when I bought it years ago....most CFM. I believe Echo now has one which flows a bit more CFM now though. Mine is -WAY- overkill for what a typical residential homeowner would want when looking to simply clean up grass clippings and such. Those smaller handhelds are the way to go. :)

What I have:

Echo's:
 
How cute, do you use it to blow out your birthday candles? ;lol :p >> Just kidding.....

I have a big back-pack blower for blowing wet leaves out of flower beds, sticks, dog crap and peeling moss off the "lawn" and blowing it all into the woods past the "weed line" :) It was the largest one out back when I bought it years ago....most CFM. I believe Echo now has one which flows a bit more CFM now though. Mine is -WAY- overkill for what a typical residential homeowner would want when looking to simply clean up grass clippings and such. Those smaller handhelds are the way to go. :)

What I have:

Echo's:
Hehe... if only you knew. ;lol Do remember, I'm the guy who hot-rodded my log splitter and uses a 6.4 liter HEMI to drive the kids to school.

I tried a few backpack blowers, but found them to be the worst of both worlds, for my particular needs. Too wimpy to cover much lawn, too bulky to get in behind shrubs in gardens. So I went with a Little Wonder Optimax EX27 walk-behind blower, a JRCO Blower Buggy, and then the BG 86 for blowing stuff out of the gardens for the bigger blower to move across the lawn into the woods.

I've had a few Little Wonder blowers over the last 40 years, and these newer ones will literally blow a person's feet out from under them, it's happened twice in my lawn. They'll also blow the grass right out of the earth, if you're not careful with the chute angle. But they can cover several acres of lawn in short order when mounted on a blower buggy.
 
  • Haha
Reactions: JRHAWK9
Hehe... if only you knew. ;lol Do remember, I'm the guy who hot-rodded my log splitter and uses a 6.4 liter HEMI to drive the kids to school.

I tried a few backpack blowers, but found them to be the worst of both worlds, for my particular needs. Too wimpy to cover much lawn, too bulky to get in behind shrubs in gardens. So I went with a Little Wonder Optimax EX27 walk-behind blower, a JRCO Blower Buggy, and then the BG 86 for blowing stuff out of the gardens for the bigger blower to move across the lawn into the woods.

I've had a few Little Wonder blowers over the last 40 years, and these newer ones will literally blow a person's feet out from under them, it's happened twice in my lawn. They'll also blow the grass right out of the earth, if you're not careful with the chute angle. But they can cover several acres of lawn in short order when mounted on a blower buggy.

I should have known! ;lol
 
I straight gassed my echo trimmer a year ago, it was a toss up as the parts were getting in the range of new unit. I bought the parts and rebuilt it just as long term reminder to pick up the right gas can ;)
 
I straight gassed my echo trimmer a year ago, it was a toss up as the parts were getting in the range of new unit. I bought the parts and rebuilt it just as long term reminder to pick up the right gas can ;)
I keep my 2-stroke mix in 1 gal cans, and my straight gas in 5 gal cans. I'm absent-minded enough that I won't say it's impossible, but I'd have to be really distracted to mix them up!
 
I keep my 2-stroke mix in 1 gal cans, and my straight gas in 5 gal cans. I'm absent-minded enough that I won't say it's impossible, but I'd have to be really distracted to mix them up!
I do the same thing. Additionally, the oil I use makes the gas a blue/green that is pretty easy to see, even in the red can.
 
I do the same thing. Additionally, the oil I use makes the gas a blue/green that is pretty easy to see, even in the red can.
I like being able to see the dye too. I would consider adding dye if my oil didn’t contain any.
 
I keep one 2.5 gal container of 32:1 for my chainsaws and leaf blower and a 1gal of 50:1 for my brushcutter.
 
I do the same thing. Additionally, the oil I use makes the gas a blue/green that is pretty easy to see, even in the red can.
-^^^^^
What he said. It is very distinct. I am surprised you did not pick up on the color difference. You seem to be a seasoned lad.
 
-^^^^^
What he said. It is very distinct. I am surprised you did not pick up on the color difference. You seem to be a seasoned lad.
I always suspected there was a color difference, but between being partially color blind (can't tell diff between dark blue, green, black) and always mixing into metal or dark red cans, I was never sure. It took me pouring into those clear shot glasses to really tell that there was a distinct difference, which is more than I had suspected at 50:1.

I keep one 2.5 gal container of 32:1 for my chainsaws and leaf blower and a 1gal of 50:1 for my brushcutter.
I used to do that, too. Then one of the old forum members here (MasterMech) who was an OPE mechanic told us ten years ago to just follow the mix ratio spec'd on the oil being used, not the equipment spec. So, for the last 10 years, I've been running 50:1 in everything old and new, and haven't had any issues.

Ironically, my single lifetime 2-stroke failure is this relatively new piece of equipment, which is actually one of the few truly spec'd to run 50:1. I have had several much older and much less reputable brands than Stihl, and some spec'd for 32 or even 24:1, which just keep running.
 
I used to do that, too. Then one of the old forum members here (MasterMech) who was an OPE mechanic told us ten years ago to just follow the mix ratio spec'd on the oil being used, not the equipment spec.
I do that too...every 2 stroke I own gets 32:1. Have never blown one up...well, not true, I did blow up a bike, but it was just plain wore the heck out. I know people swear by 50:1, but I have had plenty of those engines apart, and there is just not enough oil film on things for my liking...32:1 doesn't smoke once warmed up, so for the extra 9¢ in oil per tank, I'm going with the lil "extra insurance" more oil offers. 50:1 just offers no margin for error.
 
  • Like
Reactions: JRHAWK9
True. Back when I ran 32:1, I was measuring out my own. The main reason I switched to 50:1 was I started buying the 2.6 oz. pre-measured bottles from Stihl and others. Much quicker, cleaner, and more convenient.
 
I used to do that, too. Then one of the old forum members here (MasterMech) who was an OPE mechanic told us ten years ago to just follow the mix ratio spec'd on the oil being used, not the equipment spec. So, for the last 10 years, I've been running 50:1 in everything old and new, and haven't had any issues.

My saws have been ported and most all of the builders recommend 32:1, from what I read it protects the crank bearings more. I ran it in my forestry saw but that does not see much of a load most of the time when running the saw blade or the 3 armed blade, so I saw excess discharge out the exhaust (which I have opened up). Only time it sees a decent load is when I am running the string trimmer head on it and clearing the tall stuff. It also helps I run a thick 0.155" line on it. That's why I run that one at 50:1. I run a good clean burning oil, Bel-Ray H1-R.
 
  • Like
Reactions: Ashful
I do that too...every 2 stroke I own gets 32:1. Have never blown one up...well, not true, I did blow up a bike, but it was just plain wore the heck out. I know people swear by 50:1, but I have had plenty of those engines apart, and there is just not enough oil film on things for my liking...32:1 doesn't smoke once warmed up, so for the extra 9¢ in oil per tank, I'm going with the lil "extra insurance" more oil offers. 50:1 just offers no margin for error.

Same here. When I take the mufflers off my saws the pistons have a nice wet/shiny film of oil on them. I remember when I looked at my 346XP when I first got it when I ran 50:1 the piston looked dry in comparison. I really want to use 32:1 in my forestry saw too but I don't like the exhaust discharge at times when it's not under load for extended periods. I'm guessing the open muffler exacerbates this. It's not like I'm running a dirty oil either, as I use Belray H1-R.


Muffler with hole drilled but before deflector was added. I also drilled out most of the internal baffle, which also had a small hole, about the same size as the little pea shooter outlet shown below. :

IMG_20210421_121033809.jpg

After deflector:

IMG_20210421_180948655.jpg
 
Last edited:
Same here. When I take the mufflers off my saws the pistons have a nice wet/shiny film of oil on them. I remember when I looked at my 346XP when I first got it when I ran 50:1 the piston looked dry in comparison. I really want to use 32:1 in my forestry saw too but I don't like the exhaust discharge at times when it's not under load for extended periods.
Maybe split the difference, and mix to 40:1? Like I said, my main reason for going 50:1 was my use of pre-measured bottles with a 1 gal. can, and getting away from measuring my own.