Need some 2 cycle engine help

As much as I love my scythe, I still need my string trimmer for a lot of applications. And unfortunately the engine seized up last weekend!
First it shut down after an hour of running. I did some troubleshooting and found it would run without the muffler, so I went to finish the job w/o muffler and it lasted 20 minutes before seizing up completely. Won't turn, even manually bypassing the pull string. Same oil/gas mix as usual, and I've ran through a few tanks of the current blend.

So taking a peek inside the muffler port, I see a lot of scoring on the cylinder. I know that in rebuilding it is typical to need to smooth out a cylinder with sandpaper/emory cloth. But this looks awfully rough. Is that a "normal" amount of scoring on a cylinder? Trying to figure out if this is worth continuing to tear down for a rebuild (which I have never done before but always prefer fixing things to trashing and buying new.)

And BONUS question: What the heck is this extra port into the engine? I found it under the plastic cover. Seems to be a third hole in addition to the intake and exhaust.

hey matt

For what it is worth. I would imagine you would be able to find a replacement or even another exact model for sale, maybe even free. Do you happen to have the make and model of the string trimmer?
This might be a common problem with this model.

Our local dump person. He has ended up with multiple models of the same string trimmer. Some needed some attention(clean carb, new fuel line/filter) ran perfectly fine afterwards.

Do you have a way to source another exact model for parts?



If i had to guess. i would say it is a ventilation port for crankcase pressure. seeing as it is below the cylinder head where the combustion happens.

what brand is it, price and availability of parts is the big ?

Matt Todd wrote: Won't turn, even manually bypassing the pull string. Same oil/gas mix as usual....

What kind of gas have you been using? Regular pump gas from any gas station or no-ethanol gas?

James Freyr wrote:

Matt Todd wrote: Won't turn, even manually bypassing the pull string. Same oil/gas mix as usual....

What kind of gas have you been using? Regular pump gas from any gas station or no-ethanol gas?

I have been using regular gas for this 7 year life of this trimmer, 10% ethanol is what we have in Missouri. But your question got me looking around a bit and I see that this is not recommended for 2 cycle since the oil I mix with the gas does not bind to the ethanol like it does to the gasoline. So... I guess no more E10 in my small equipment from now on!  

I guess if it's an expensive model you might pursue it further. Or even take it into a shop and ask the front desk guy if it's worth it.

If it's an inexpensive one, my gut reaction is "abandon it and move on."
Unless you can scrounge another engine as suggested above.

[Although: this comment is from a guy who fixes unfixable computers just to see if he can do it. So if there's a challenge/fun element, that changes things.]

We have to take the filters out of ours and run for a while then clean or replace them. If it’s hot out they have a really hard time running as well. We use a 50 to 1 ratio for our mix. Not sure if that’s helpful but there you go. Lol

Matt Todd wrote:
I have been using regular gas for this 7 year life of this trimmer, 10% ethanol is what we have in Missouri. But your question got me looking around a bit and I see that this is not recommended for 2 cycle since the oil I mix with the gas does not bind to the ethanol like it does to the gasoline. So... I guess no more E10 in my small equipment from now on!  

I didn't know about the oil not binding to the ethanol thing. This sounds like a second fatal blow to 2-strokes, at least. I knew of ethanol ruining small engines, both 2-stroke and 4-stroke air cooled engines, as ethanol burns way hotter than gasoline, which ends up scorching piston rings and cylinder walls among other damage. If non-ethanol gas is difficult to find for folks in cities, check nearby local lakes for marine gas. It's non-ethanol as ethanol can ruin boat engines also.

I've paid the extra to get ethanol free "premium" gas for all my small engines.  And I put Stabil in it from the get-go.  Also, last time I saw the state inspector at a gas station he said that they pump 3 gallons of gas from a pump before they assume the previously selected grade of gas is out of the system.  So I put the first 3 gallons in my vehicle and the rest go into the lawnmower's gas can.

I race 2 stroke motorcycles.
Those score marks are a sign of death.
When hard pressed I have melted the build up on the cast iron that caused those grooves, fitted new pistons and rings, adjusted the tuning and gone out again.
Words such as sandpaper should not be used!!!
Different fuels will react to different oils, I have blown up engines shaking the oil instead of cascading the fuel over the oil sitting in a small cup inside a larger container.
Some 'oils' can be very difficult to work with.
That extra port maybe the transfer port between the crankcase and the combustion chamber.

I use 100% ethanol / methanol and it needs to be washed out after every run to prevent internal damage.

Thanks for the advice all. I did tear this one down to access the piston (hammer and a dowel!) There was some awfully bad scoring so they are indeed toast. I did fiddle with sanding those down just to see if the piston would move. And it does, but pretty sure in doing so I went too far and now it doesn't hold compression.

Repair means buying a new piston, cylinder, piston ring, and air filter for around $60. So I'll give that a try since I like it and am happy with this model and already have a brush cutter adapter for it that works well.

The alternative is $200 for a new decent trimmer plus whatever it costs me to get a brush cutter adapter for the new guy.

I've always wanted to have a better understanding of 2 cycle engines anyhow. Plus this fits with the permaculture way of repair vs replace!

Make sure the piston rings have a small gap where the two ends of the circle meet when inside the cylinder.
Thats inportant to allow for expansion.

I have melted the aluminium build up with acod on the side of the track!!

When rebuilding if you need to clean aluminum off of iron I use muriatic acid.  I strongly suggest cleaning the carburetor jets to make sure you have the proper fuel mix.  The fuel filter may look clean, but could be plugged with slime.  I blow through them backwards to make sure before reusing it. The fuel lines sometimes get so soft they collapse while running and cause the engine to run lean and get hot.  I run into plugged exhaust quite often too.   One of the most beneficial things I have found is I never run our equipment over 85 degrees outside temperature.  I have found most small engine will not keep cool enough.  

Like John, I have ran ethanol and methanol for a long time without issues.  My ethanol converted 1974 Briggs 3 hp mower loves hot weather.  The evaporation of ethanol pulls a bunch of heat away from the intake and the engine runs much cooler.  I experimented with it one day when it was around 80 degrees and ran it for 1/2 an hour trimming.  When I went to change the oil right after that it was only luke warm.  I use 2 fuel caps for the ethanol mower. One is glued shut so when it is in storage water doesn't get into the fuel tank.  Water plus ethanol or methanol become acidic.  Acid plus 3 types of metals in a carburetor becomes a little battery and corrodes all up.

Christopher Shepherd wrote: I strongly suggest cleaning the carburetor jets to make sure you have the proper fuel mix.  The fuel filter may look clean, but could be plugged with slime.  I blow through them backwards to make sure before reusing it. The fuel lines sometimes get so soft they collapse while running and cause the engine to run lean and get hot.  I run into plugged exhaust quite often too.   One of the most beneficial things I have found is I never run our equipment over 85 degrees outside temperature.  I have found most small engine will not keep cool enough.  

Thanks for the info. I was considering a carb job while I had it on the bench. The two factors you mentioned: Clogged jets causing the engine to run lean and hot, combined with over 85 degrees (which it was when I broke down) could well be factors in the piston expanding and scoring.
With a replacement carb pricing at $65 to $80, that put me over the line of "buy a new unit." I don't have the confidence to tear down the carb for cleaning with all those tiny parts! And they don't make a cleaning/rebuild kit for mine. I did come across this $15 aftermarket carb with new fuel lines and I'm sorely tempted: https://www.ebay.com/c/818521259  

Update: I tried to do the right thing. Ordered parts, was told it would be 7 to 10 days before received from manufacturer. Over 3 weeks later and nothing. The parts guys stopped answering my emails asking if these were actually available from their manufacturer. So I guess it's about time to cancel the order and just buy a dang new weed wacker because I can't go forever without!

Lesson learned: repairing machinery only works if the parts are available.

the only ones really worth rebuilding are the stihl pro models. built like the picture you show where the cylinder bolts to engine block.

you never mention what model or brand your machine is.
my experience with weed eaters is that ive had many, all different brands. echo brand is fairly decent, ryobi used to be decent, but for some reason the stihl professional stuff is heads above the rest. It must have been at least 15 years ago. I had no less than half dozen different weed eaters, all the major brands in the shed I had accumulated over the years. one spring trying to get just one of them going turned out to be super frustrating and very costly being new parts and lots of cord pulling with very little successs getting one to run properly.
I was at wits end fortunately at the time I had good income. went to stihl dealer and got a km130. its still going strong and starts every time I pull it out of the shed with just a couple pulls of the cord. I always use stihl oil mixed with non ethanol high octane gas.
its not cheap but is a one time investment that paid for itself over the years.
I think it is very important to use non ethanol gas in any small engine in attempt to ensure longevity
just $0.02 from an old phart

what I'm really looking forward to are the developments in rechargeable battery powered. I gotta feeling it won't be too much longer and battery power tools will be equal to or better than gas powered stuff.

With 36V battery mowers now, a weed wacker should work nicely with one of those battery's.

bruce Fine wrote:what I'm really looking forward to are the developments in rechargeable battery powered. I gotta feeling it won't be too much longer and battery power tools will be equal to or better than gas powered stuff.

We have been using a 56v ego weed eater for about 2 years now. It works for about 45-60 minutes. Than it needs to be charged which takes about 50 minutes. It often works quite well as i hardly want to spend 4 hours weed wacking.
Plus it works with having multiple things to do in the day. 45 minutes of weed eating and than moving on to something else. I means job/tasks can be done in small increments, which i like.

I have an Ego weed whacker , a self propelled lawn mower and a chain saw!  Two battery's a 7.5 amp for the lawn mower and a 2 amp for the weed wacker.  Chainsaw uses which ever is currently charged.
All three work superb!  Highly recommended!

OP has probably dealt with the situation by now, but just to write it down for folks who have this question in the future:

- first and foremost: YES to ethanol-free gas! There are a few search engines to find it. Ethanol gas is like the sworn enemy of 2 stroke engines.

- $10-15 replacement carbs have actually worked decently for me. They won't hold a tune all that well, but you get to a point where you can throw a tune on it in five minutes.
- China engine rebuild kits are of variable quality (inspect the pieces when you get them, 1st cylinder they sent had a huge casting flaw but the 2nd was nice) but the one in my Stihl chainsaw has been going strong for years. Build philosophy is different from ours, it will run like complete garbage for the first tank of gas while the parts bed in. I was at the point of giving up when I realized it was starting to make a LOT more power! That's when the parts figured out how to work as a team, and the primitive cylinder ring wore itself into place. It's been a beast ever since.
- Do expect you'll have to improvise small stuff if you go this route. They sent an 026 pro cylinder for 026, I don't have a top plastic that works with the decomp port that an 026 doesn't need anyway. (026 pro has a decompression port to make it easier to crank over) You do need the plastic, it guides air so the engine won't overheat. What to do? Trimmed an appropriate sized bolt, Teflon tape, cinched down just enough (remember: aluminum block), good to go.
- Ditto on no mounting studs for the plastic. Make studs from bolts: the ghetto way is to double-nut them as though you were taking out a stud, then put one more nut between the double nut and the bolt head. Tighten bottom 2 nuts against each other so you have something to pull against with your wrench, then trim to appropriate length and use the 3rd nut to straighten out the threads enough.
- If you order stuff from China, best plan is to set the equipment aside and try to forget that you ordered it. It will take weeks, if not a month or two, to arrive and that's especially true now that the trade routes are down.

I didn't want to go the China route, but I had already used up some American parts attempting to save the existing cylinder and the budget for repairing that saw was done. The China parts made the difference between throwing it away and having a working saw.

Photo for fun. I have the new (correct) piston now and I'm left with a question: Do I need to hone (or otherwise "prepare") the brand new cylinder? The internet seems to have mixed feelings about honing new cylinders on small engines.

My Opinion;
Do not hone. Your more likely to damage the finish rather than help it.
Now take my "opinion" and put it in one hand...  fill the other hand with...   which hand has something in it...

Hello,
Having worked on a variety of 2 cycle engines, I wouldn't hone the cyl. I would clean and blow off with air, and lube with oil for installing. There can be some kind of coating on the cyl/ wall that IS NOT MEANT to be honed. I am running reg. gas and have been for the 45 yrs. I've been using 2 cycle engines. I do not leave fuel in engine or tank and run through when engines are not going to be used for some time.

Final follow-up: It lives!!!
Just in time for everything to green up.
There is ZERO consensus on what the break-in procedure should be, so I'm averaging what I read and doing three cycles of "bring up to operating temp with varying RPM's and cool down" before I turn it loose on the lawn.