String Trimmer Motor

rdw777 Mon Jun 12, 2023 2:44 pm

Cheapie Murray from WM about four years old….. Started losing power and getting hard to start so I decided to look into it…. Just a big model airplane motor right?….Spark, Fuel good so kept digging….Pulled the plastic backplate off to look inside….. Found it to be the backplate itself….. Crank pin had cut a grove and ultimately all the way thru ….

Another thing I found odd is that the crank pin is free to float, Not fixed to the crankshaft….Also that the crank pin has chamfered ends that are practically a sharp edge that could meet the backplate

So I covered up the hole with JB weld and rounded the end of the crank pin in the drill press to hopefully keep from digging in further….and got the power and ease of starting restored…. I’ve since found where I could order the back plate (cheap) so I’ll get another and keep this cheapie trimmer going for awhile….. Thought my fellow “engine guys “ might like to see this….

rsv1cox Mon Jun 12, 2023 3:46 pm

Way to go Robert, I always admire someone that repairs things back to full use. I went through many gas stringers that you feed line. Finally gave up and went electric to a Black and Decker Weed Eater that you just clip pre-loaded line canisters to. Not sure if your's does that, but I'm never looking back.

**Admin** Tue Jun 13, 2023 12:24 am

Nice repair!

Folks do take trimmer/leaf blower engines and turn them into large RC plane engines. I know someone who did that.

Oldenginerod Tue Jun 13, 2023 2:26 am

I'd be very dubious about making a JB Weld repair inside the crankcase. Just needs a small chunk to come free and shoot up the bypass, lodges in the port and rips a hole down the side of your piston. If a new backplate is still available I'd be doing that. I think the current repair will be very temporary and the results of a failure devastating.

Rod.

rdw777 Tue Jun 13, 2023 9:59 am

Thanks Bob, I know you’re the kind of fella that keeps your equipment in good condition and gets a good service life as well….. I think a little “want” in early life was a good thing…. Taught us how fix and make do….I like the handle on the Black and Decker…. The straight shaft on mine is tiring on the wrist….Will look for similar when it’s time Very Happy

Folks do take trimmer/leaf blower engines and turn them into large RC plane engines.

Thanks Jacob…..I think that would be a fun project…. There’s many options now for large gas engines but I think it would be fun to go thru the steps to do a conversion for the do it yourself-er…… Maybe when I can’t see the little ones anymore …. We could go to the lawnmower shop for parts LOL!!! Very Happy

I'd be very dubious about making a JB Weld repair inside the crankcase.

Thanks for the heads up Rod, It’s repaired from the outside, I should have noted that….. I will still order the new part because of the groove worn in the old one…. But would be a neat experiment to see how long the patch would hold up to the heat and oil…

Robert

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