Weed Wacker Died

[woody]

My Craftsman weed wacker died and after doing all the normal diagnostics I tore it completely apart to find a scored piston, cylinder and the exhaust port almost plugged. I have my opinions of what caused this but would like some opinions of others also. the blackness of the oil is a concern as well as the stickiness of it, had to wash my hands several times to get it off maybe not 2 cycle oil not sure. what would cause it to carbon up that much in just one and a half cutting seasons? the cylinder I wash with carburetor cleaner but the piston I left dirty so the picture would show the oil. This weed wacker was built by Troybilt and I like being able to use my drill to crack it especially when working on it.

 

[CobyRupert]

I'm going follow this thread as I'm curious to know too.

I always wonder about ethanol gas breaking down seals (so I hear?) and allowing air leaks, and the motor then runs too lean and hot (for a little while ) until it craps the bed. But if too hot / too lean , it wouldn't seem you'd have all that blackness. I usually associate that with too rich.
???

Do you think it was the wrong oil? That it didn't lube well, causing the scoring, but left residue?

 

[woody]

Do you think it was the wrong oil? That it didn't lube well, causing the scoring, but left residue?

yes that is what I was thinking, but maybe it is the aluminum mixing with the gas/oil mixture leaving it black. The wife tried cranking it for about fifteen minutes and gave up then I tried to crack it using the drill but could not get it to crank, she said it just quit running while she was using it. we have always used stihl oil but our son uses it at his house and I can not be 100% sure what was used in it once out of my sight.

 

[Oldoak]

From the looks of the cylinder wall, my first guess would be someone didn't mix any oil with the gas at some point.

I don't believe using ethanol blend gas had anything to do with the failure. At least not 10% ethanol gas. I have been using that for several years now without problems.

 

[Paul Thornton]

Following also.

 

[Thomas]

Many years back had Sears trimmer same causes fuel/oil was mix right,but running long period time full throttle did it in when cutting high grass/hay.

 

[CobyRupert]

From the looks of the cylinder wall, my first guess would be someone didn't mix any oil with the gas at some point.

What is all that black residue? Is it just from the gas/oil that's getting run through it when OP's wife cranked it for 15 minutes (plus more cranking with drill) when there's no compression?

I'm no expect, so hopefully others chime in, but IMHO: It's my understanding you have that scoring from either a old motor that's accumulated them over a long life and just got tired out, or from running it with insufficient oil. Where the insufficiency can be caused by not adding it to the gas mix correctly (or at all) or running it too lean. Where the leanness can be caused by many factors (carb setting, air leaks (too much), fuel restrictions (too little).

 

[CobyRupert]

Many years back had Sears trimmer same causes fuel/oil was mix right,but running long period time full throttle did it in when cutting high grass/hay.

Maybe carb setting was right for low speed jet / idle setting, but not for high speed jet setting?

When in doubt I'd rather set them rich, and have to replace/clean plugs and sacrifice some power than burn them up.

 

[hawkeye08]

We recently purchased a Stihl FS70 trimmer.

The sales guy told us to use non ethanol gas if possible and Stihl oil... not required, just better results.

He also told me to prime it with the primer bulb 3-5 times each time I needed to start it, even it is was already warm. My belief is this provides some extra lubrication for starting.. I have not looked into it technically, but it appears that the primer bulb squirts some fuel into engine. I see no reason to do this on a warm engine that starts right up other than lubrication..

 

[woody]

Thanks for the replies, everyone pretty much is confirming what I suspected. what we did to fix the problem is since Sears in our town is going out of business we went down and bought us a new one at 30% off and the son went down and bought his own. The old one never sounded like it was running lean and the only thing we can figure could of happen is either the fuel and oil was not mixed properly or someone got the wrong jug of gas "not likely since our gas is in a five gallon metal can and the two cycle gas is in a red plastic container with 40 to1 wrote on it.