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Mike Burdick
04-27-2008, 04:22 PM
I was looking at some weed trimmers (commercial rating) and noticed that a few manufacturers are now making them with a 4-cycle engine.

I'm curious if anyone has purchased a 4-cycle model and, if so, do they have a pressurized oil system? I would think that a 4-cycle engine on a weed trimmer would be about the last thing wanted with respect to horsepower/weight and lubrication considerations.

J Tiers
04-27-2008, 04:47 PM
I would think that a 4-cycle engine on a weed trimmer would be about the last thing wanted with respect to horsepower/weight and lubrication considerations.

But the only thing the EPA will let you sell................

2 stroke are hated and forbidden because they blow out so much unburned oil and fuel in teh oil-mix versions.

Making a "real" (non-oil-mix, air scavenged) 2 stroke would be too expensive, and is not done. Or, possibly, the legislation was written without realizing that a 2 stroke as-described would be no diifferent from a 4-stroke type........ and just blanket forbids ALL 2 stroke.

Bill Pace
04-27-2008, 04:56 PM
I got tired of the 2 strokers getting ornery to start and not idling after about 3-4 years, so back in ---00-01?, I think it was, I started doing a little research on the 4 strokers and wasnt too impressed, seemed the carbs were the problem, just couldnt handle an all-position run. Dont recall any mention of oil probs. Anyhow, a few months passed and Ryobi started making noises that they had cured the carb problem and since I was totally PO'd at the current 2 stroke, I bought one.

I LOVE IT!!

Weighs a tad more but even after these 6-7 years it'll start on 2nd-3rd pull and will idle perfectly. Has way ample power in any position --- I have to do a LOT of walk trimming with it on its side, and it dont faze it, and living rural I'm constantly fighting vines, -- saw briers (thats a tough brute), poison ivy, virginia creeper, etc, and vines will tell you what a trimmer is made of...

No doubt they have been improved on even more in the time span since I bought this one

Fasttrack
04-27-2008, 05:07 PM
Yep - I won a four cycle about a year ago at a "skills usa" small engine competition. I haven't opened mine up yet, but it weighs 11 lbs and has more horespower and torque at 6,000 rpm than similiar two strokes. (6000 rpm is the "optimum" rpm for most weed eaters. You can rev 'em higher but if you read the manual they tell you not to be full throttle for more than like 5 seconds or something)

Anyhow, I like the idea. Not significantly heavier and I think they've really thought this one through. Its hard to break into a market that was so dominated by two-strokes and keep your customers happy. I suspect they spent quite a bit of time producing a four-stroke that behaved just as well if not better than two strokes.

just my humble opinion.

<edit> actually don't quote me on the rpm ... i can't remember for sure what the figure was but the point is that at the rpm that most two-strokes run for best cutting action had less power than the four stroke did at the same rpm. Basically the manufacturer was just trying to prove that a four stroke could perform as well as a two stroke.

kendall
04-27-2008, 05:22 PM
Have an old ryobi I picked up free a long while ago, 4 stroke, actually runs pretty good.

It takes quite a bit of abuse without complaint, and to me the best part is the sound.I hate the scream of most two strokes.

It is not maintained at all, use it once or twice in the spring to clear out the growth near the house and garage, then drain the gas and toss it in the shed till next spring. Most I've done in 8 years is clean the plug and change oil.

They are more critical of the way they're stored, my old two-strokes I hung motor down from a rafter, the four strokes leak in that position and need to be horizontal or engine up.

Ken.

bhassan
04-27-2008, 07:03 PM
I was looking at some weed trimmers (commercial rating) and noticed that a few manufacturers are now making them with a 4-cycle engine.

I'm curious if anyone has purchased a 4-cycle model and, if so, do they have a pressurized oil system? I would think that a 4-cycle engine on a weed trimmer would be about the last thing wanted with respect to horsepower/weight and lubrication considerations.
Mike,

To specifically answer your question, no, the oil system on my 4-stroke Toro (at least) is not pressurized. It is "splash-lubrication," like that of most push lawnmowers.

And I agree with all the other posters. This thing is ten times better than my previous Ryobi two-stroke...easy to start, low maintenance, simple carb, etc, etc.

Bilal Hassan
Clarksville, MD

IOWOLF
04-27-2008, 07:27 PM
I guess I am the oddball here I have had a Ryobi 4 cycle for 7 years but I will pick up my 2 stroke every time, I am guessing the reason I have such good luck with it is because I never drain it for winter use staybill in it and also use Bell ray MC1 for the mix.

My weed eaters are the Q/C type, and I only use the 4 st. one for the tiller tool, and never for the pole saw, it doesn't like being upside down.

Your mileage obviously differs.

Mike Burdick
04-27-2008, 07:38 PM
But the only thing the EPA will let you sell................

2 stroke are hated and forbidden because they blow out so much unburned oil and fuel in teh oil-mix versions.

Making a "real" (non-oil-mix, air scavenged) 2 stroke would be too expensive, and is not done. Or, possibly, the legislation was written without realizing that a 2 stroke as-described would be no diifferent from a 4-stroke type........ and just blanket forbids ALL 2 stroke.

Hmmm...Stihl still makes a 2-stroke trimmer and a whole lot of other tools...drill, chainsaws... I bought the FS-250. As for lawn mowers, you are probably correct.

IOWOLF,

Yeah, I must be "old fashioned" too! I like the 2-cycle since the tool gets put in all sorts of positions as it is used. Hard to believe that the 4-cycle doesn't have a presurized oil system...I wonder how long they will last!

Fasttrack
04-27-2008, 07:51 PM
I've seen a techumseh run for three months of regular lawn mowing use with no oil in the case ... It was toast after those three months but I don't think running your little four stroke for a few minutes in a funny posistion is going to hurt it any. Besides, the splasher is likely long enough and the case large enough that at all probable angles of use it is still splashing oil. How often do you use a weed whacker pointed straight at the sky? Think about the range of angles you use it over - its really quite small. There is maybe plus or minus 45 degrees tilt and +/- 20 degrees up/down.

Small engines are hard to kill. There's not too much to them really.

GNO
04-27-2008, 08:01 PM
I looked at a stille sp? about a year ago it was a 4 stroke charging through the crankcase and using a 50/1 gas/oil mix if I remember it gained a slight supercharge effect

Bill Pace
04-27-2008, 08:04 PM
and never for the pole saw, it doesn't like being upside down.

Your mileage obviously differs.

Yep, here again, my milage varies.....I got the pole saw attachment, and have used it quite a lot in the 'upside down' position and it doesnt know the difference.....

J Tiers
04-27-2008, 09:12 PM
Hmmm...Stihl still makes a 2-stroke trimmer and a whole lot of other tools...drill, chainsaws... I bought the FS-250. As for lawn mowers, you are probably correct.


My understanding is that it is being "phased in"...... but maybe they haven't noticed weedeaters yet, and some manufacturers are just getting ahead of the curve..

I CAN say that I would be happy as a clam if I never heard another screaming 2 stroke weedeater or &^%$# dog-crap blower (leaf blower is what they are sold as). You can hear them for a long way, and all the lawn services use them.

They cut the grass, then trim with the weedeaters, and finally blow the trimmings, along with all the crap and dust, back into the yards..... most of the dust ends up a block over. And you can hear them for 3 blocks.

A 4 stroke wouldn't fix the dust, but the sound is less grating.

jcarter
04-27-2008, 09:55 PM
We had two Stihl four stroke brush cutters at work. Both suffered catastophic failures. Valves broke off destroying the engine. After some investigation I realized both failures occurred while the unit was being used with a string trimmer head attached. The trimmer line was quite short on both heads. If the trimmer line is allowed to wear down the engine rpm increases dramatically. These little engines will experience valve float which will cause a valve to impact the piston breaking the valve. We went back to the two strokes. I am sure the four stroke would be fine in the hands of someone who has common sense but we have twenty four highschool kids who do our trimming and other such jobs. These kids don't give a damn about equipment . We also had a Honda four stroke and a Red Max four stroke for a while. We found if these units were carried upside down oil would leak out of the crankcase vent and into the air filter. The engine would hydrolock while attempting to start it. Again, trying to tell these kids to carry the unit upright fell on deaf ears. We got rid of the trimmers and went back to Stihl two strokes.

Fasttrack
04-27-2008, 11:09 PM
Jcarter makes a good point

Like others have said, you need to store a 4-stroke appropriately and they are not high rpm units by nature. Its surprsing, however, that they were not governed. Thats the main reason why 4-strokes are governed is to prevent those kinds of catastrophic failures. To expierence valve float and break a valve you've either got to be hoppin' along incredibly fast (remember these are mechanical, no pump up like with hydraulic lifters) or have some very worn out springs. Maybe they had heat issues before hand that weakened the springs.

Evan
04-28-2008, 08:00 AM
With proper design on a small engine like that valve float can be the governor.

A.K. Boomer
04-28-2008, 08:56 AM
To expierence valve float and break a valve you've either got to be hoppin' along incredibly fast (remember these are mechanical, no pump up like with hydraulic lifters)



Hydraulic lifters are just an adjustment means, they still abide by all the mechanical interference fit rules.

A.K. Boomer
04-28-2008, 09:22 AM
I looked at a stille sp? about a year ago it was a 4 stroke charging through the crankcase and using a 50/1 gas/oil mix if I remember it gained a slight supercharge effect


I would like to tear into one of those, Your giving up one hell of an advantage though (running the lower end in pure oil, and not burning your oil along with the fuel), but a cut above a two stroke in emissions due to a positive valve train duration, Two strokes are dirty for 2 reasons, 1, they mix and burn and 2, they dont have absolute control over there intake and exhaust cycles --- weedeaters have an advantage as they usually run at a pre determined RPM and can be port designed to reduce throwing part of the intake charge out in the exhaust cycle and there are variable port designs to cover a good part of a usable RPM range -- but still they lag as compared to the slight over lap period of a four stroke and almost complete exhaust elimination and fresh charge,,,

This design you speak of one ups the typical two stroke (they run off of the supercharge effect also) as it would be a "double pumper" --- perhaps you could store it in a small plenum and get a great timed flow/pressure effect.

GKman
04-28-2008, 09:23 AM
ToMAto? ToMAT0?

Both 2 and 4 stroke engines work on the Otto cycle: intake, compression, power and exhaust. One does it in two strokes the other in four. There are no two or four cycle engines.

A.K. Boomer
04-28-2008, 09:40 AM
In general the Best way to deal with Valve float Is to handle it electronically AND have the proper clearance between Valve's and pistons, Actually a weedeater can do it just electronically as its Almost impossible to over-rev one without its own power (unlike a car coming down a steep grade that you can throw a wild shift and stuff the valves even if its electronically protected)

In rare instances one could be running extra hot and turn its spark plug into a glow plug and override the electronic saftey, but odd are the timing would be off too much too achieve extreme RPM's


Consistantly Utilizing Valve float as a means of controlling RPM is done in many situations --- But Im a purist, I dont like it, Its archaic at best and if its experienced all the time it will cause pre-mature wear as it will even pound the hell out of stellite valve seats after awhile and definitly deform the valves margin...

A.K. Boomer
04-28-2008, 09:43 AM
ToMAto? ToMAT0?

Both 2 and 4 stroke engines work on the Otto cycle: intake, compression, power and exhaust. One does it in two strokes the other in four. There are no two or four cycle engines.


What? Hello ----:confused:


I believe the discussion is the basic 2 stroke is supercharged .


Edit; You do bring up a good point, I have heard people say "2 cycle" and never really stopped to think about it being wrong, Its how many strokes complete all the cycles and its a big difference...

And yet one last edit; GKman, im sorry for being so rude, Your post makes perfect sense and also brings up a great point, but most importantly --- I got impatient because i searched through the entire thread and didnt see where you got off on the "cycle" topic to begin with --- and now I see its wrapped up in the very title... My Duhh,,,, Please give me some credit as I could edit my boo-boo's out so I wouldnt have to eat any crow, but that would mean im a weasle and im not, plus --- you put some A1 steak sauce on it and its really not all that bad U know ;>}

Fasttrack
04-28-2008, 10:20 AM
Hydraulic lifters expierience pump up at high rpm and leave the valves cracked open. This leads to loss of compression, oxidation of the seats and can cause the valve to interfere with the piston. Especially if it is a poorly designed head.

Thats why high lift radical cams use mechanical lifters, not hydraulic. You get better response and higher rpm without valve float.

Evan
04-28-2008, 10:39 AM
Thats why high lift radical cams use mechanical lifters, not hydraulic. You get better response and higher rpm without valve float.

Desmodromic valve trains don't float. IIRC it was Ducati that developed the desmo system.

A.K. Boomer
04-28-2008, 10:46 AM
Hydraulic lifters expierience pump up at high rpm and leave the valves cracked open. This leads to loss of compression, oxidation of the seats and can cause the valve to interfere with the piston. Especially if it is a poorly designed head.

Thats why high lift radical cams use mechanical lifters, not hydraulic. You get better response and higher rpm without valve float.



I understand what your saying now, This actually rears its head when people start pushing the limits and taking some engines beyond the intentions for what they were designed for, On that I will agree -- lots of guys dont even think about it --- they will actually put on a higher volume oil pump with standard pressure relief and then spin it at faster RMP's!

What your talking about is evident with either bad design or people going way beyond and creating bad design ---- Hydraulic lifters are fully capable of remaining a constant throughout any RPM range if they and all the other systems guiding them are kept in check, seen too many High revin little Japanese engines that can testify to that.

A.K. Boomer
04-28-2008, 10:59 AM
Desmodromic valve trains don't float. IIRC it was Ducati that developed the desmo system.



Many many companies have had a Desmo and way before Duke developed theirs --- although I believe Dukes have the best system ever utilized,
Puegot had a desmo in 1914, mercede's had one very early also..

Swarf&Sparks
04-28-2008, 11:04 AM
I doubt many of us could afford a desmo weed whacker! :eek:

A.K. Boomer
04-28-2008, 11:10 AM
Yeah but youd be the envy of all the neighbors :p

Swarf&Sparks
04-28-2008, 11:14 AM
With square slide Delllortos? Nah!
;)

Lew Hartswick
04-28-2008, 06:13 PM
I see the auto "nuts" have beat me too it. I was going to mention the
Mercedes 300 SLR . :-)
...lew...

retusaf99
04-29-2008, 12:49 PM
I was looking at some weed trimmers (commercial rating) and noticed that a few manufacturers are now making them with a 4-cycle engine.

I'm curious if anyone has purchased a 4-cycle model and, if so, do they have a pressurized oil system? I would think that a 4-cycle engine on a weed trimmer would be about the last thing wanted with respect to horsepower/weight and lubrication considerations.
Back to the OP's original question, I recently purchased an MTD brand trimmer from Costco. It has a 25cc Honda 4-cycle. Just splash oiling as far as I can tell. Very quiet idle, more power than I need for trimming our 1 acre. I wouldn't call it quiet at 5k or 6k rpm, but better than my old WeedEater brand 2-cycle that lasted 10 years (just got too hard to start.)

BTW, the Honda engine says made in Thailand, and this MTD is built in Mexico. I don't use this in a commercial setting, so ymmv.

I like it.

Doug

PhilR
04-29-2008, 07:58 PM
The honda 4stroke is supposed to turn the oil into mist. Oil mist is run through the engine by crankcase pressure and reed valves.
My dad bought the 31cc honda with it first came to Canada. We first put it into a kayak, then it went on a bicycle for a bit. It has been a good little engine. I think it needs some new diaphrams the carb now. Might make a good engine for giant rc plane.

Ian B
04-30-2008, 12:48 PM
I also switched to a 4 stroke weed whacker (known as "strimmers" in the UK I think). Easy starting, easy to use and enough power.

Anyone have recommendations on what kind of cutting head to use? Mine has one of those evil mechanisms containing nylon cord, a spring and a spool that's supposed to feed more nylon out when you rev the engine and whack the cutter head down. Rarely works - the nylon cord keeps friction welding itelf together on the spool.

Ian

topct
04-30-2008, 02:54 PM
Might make a good engine for giant rc plane.

Scroll down a bit,

http://www.carrprecision.com/Pages/prod02.htm