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Two-cycle weed trimmer

Thu May 24, 2012 6:54 pm

While I have understood the principles of the two-cycle engine for well over 60 years, some of the parts of the engines have been baffling. But I continue to learn and improve my abilities with them. Just repaired, by myself, a couple of them donated to me by frustrated owners. My favorite two-cycle mechanic, much younger than me, has a serious chronic disease plus a drinking problem plus hanging out with "bad friends" which all adds up to being mostly unavailable lately. But he will take a few minutes to offer advice.
I suspect that regulations will eliminate most two-cycle engines in the not-too-distant future. But for string trimmers, I do not think the 4-cycle is the best choice even though I have not used one. The 4-cycle has a crankcase and certainly depends on gravity to keep the oil in the proper place in the sump. I have not looked inside one of those engines. But the many positions in which trimmers are used leads me to believe that some positions would starve the engine for oil. Some comments from users support that notion. But i could be wrong.
Anyone ever used a 4-cycle trimmer?

Re: Two-cycle weed trimmer

Thu May 24, 2012 8:48 pm

Bus Driver wrote: The 4-cycle has a crankcase and certainly depends on gravity to keep the oil in the proper place in the sump. I have not looked inside one of those engines. But the many positions in which trimmers are used leads me to believe that some positions would starve the engine for oil. Some comments from users support that notion.


Not if it runs on pre-mix.

http://www.stihlusa.com/whatsnew/news_fourmix.html

http://www.youtube.com/watch?v=eWZfRdm9u9c

Re: Two-cycle weed trimmer

Fri May 25, 2012 5:47 am

Interesting. Mixed fuel is still required. Says it meets emission standards. The Ryobi I looked at had the crankcase oil fill plug as expected for 4-stroke engines.

Re: Two-cycle weed trimmer

Fri May 25, 2012 7:51 am

Considering the small engines are normally splash lubricated with no pump, I expect the trimmers take that into account, and the the crankcase narrow enough, and oil is deep enough for it to get slung all over the place in most any position.

Re: Two-cycle weed trimmer

Fri May 25, 2012 9:38 am

Here's some experiences from my "other" hobby. We've been using 2 cycle string trimmer and chainsaw engines in R/C aircraft for nearly 2 decades. (giant scale) We fly inverted, stalls, and every imaginable position without difficulty. Then the four strokes appeared, and immediately grabbed attention due to it's sweet sound. However, it was found that they were heavier and produced less HP than their 2 cycle counterparts. When flown inverted, and vertical, they did not have the lifespan, due to lack of lubrication.
Weight and dependability are big issues when It comes to planes which sometimes have 8 - 10+ ft wingspan. These things will hover. Personally, I perfer my planes not to sound like a chainsaw, so I don't do "gassers" and stick to 4 cycle "glow"engines without a sump. (Giant Scale is 80"+ wingspan) I believe the sump on a string trimmer is engineered to be adequate for any position you should find yourself, as long as used for a trimmer. (Just like John indicated)
Ricky's link about Stihl's "sumpless" may now give us another option, as "glow fuel" is $15.00 a gallon... Thanks
(I've been slacking off a bit from the aircraft since I became interested in Cubs...hehe)
Regards,
Stan

Re: Two-cycle weed trimmer

Fri May 25, 2012 5:22 pm

I would think that anyone clever enough to keep the fuel flowing when an engine is turned to odd positions should be clever enough to keep oil flowing in the same positions.

Re: Two-cycle weed trimmer

Fri May 25, 2012 7:31 pm

Hard to beat a Stihl 110 we run them at work and I use them at home 4 stroke and handlebars , straight shaft.

Re: Two-cycle weed trimmer

Fri May 25, 2012 8:41 pm

The fuel systems are pretty simple in airplanes. The tank has a "clunk" which is attached to the carb. In glow engines, most have a pressure tap directly into the exhaust and keep the tank pressurized. (a few have pumps that work off vacuum pulse or crankshaft) For gassers, it's just like a string trimmer...diaphram pump in carb. (maybe an additional pressure tap into the exhaust if needed) Lubrication on the other hand may require a gear driven pump and tank like some race cars. (with a clunk inside) A lube tank would add more weight than most builders would tolerate. It's all HP vs weight with the contests. The way some are flown, one sputter at the wrong time makes the difference between landing or going home with a trash bag full of balsa & fiberglass. (sorry to drift off subject) I will be looking into the sumpless 4 strokes for a future build...
I've made the "walk of shame" to the crash site with a trash bag a number of times... Oh well...
Regards,

Sorry for running on, Bus Driver....

Re: Two-cycle weed trimmer

Fri May 25, 2012 9:12 pm

You know sdurnal, if you've got some pictures of your planes, I'd like to see them. :{_}:

Re: Two-cycle weed trimmer

Sat May 26, 2012 7:29 pm

I think that can be arranged... lol I should be able to scare some up. I'll have to upload from work, as my home system is a bit slow for pics..
Regards,
Stan

Re: Two-cycle weed trimmer

Fri Jun 29, 2012 11:05 am

Agree with SDurnal. They are getting some amazing horsepower out of lightweight 2-cycle engines. A 5 HP engine is now smaller than a weed-eater engine. (note: 5HP can run your push style lawnmower)
The new ones use VERY LITTLE oil. The airplanes mix 80:1 or 120:1 and use high quality lubricants in the fuel.

Re: Two-cycle weed trimmer

Fri Jun 29, 2012 2:01 pm

I have a Troybilt 4 cycle string trimmer. No mixing. It doesn't get the rpm's of a two cycle, but otherwise I've had no problems.
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