Why not? Puzzler

Puzzler from email, answer from today. My question, why not? Piston engine aircraft are 4 stroke, they fly upside down.
Answer to Puzzler:
So, why has no one put a four stroke engine on a chainsaw? Most all other things have been converted to a four stroke engine by now. Snowblowers, lawn mowers, Saabs… Everything but your electric razor and chainsaws. The one machine which I’ve never seen have a four stroke engine is a chainsaw. Why is that?

Well, the reason things like chainsaws have two stroke engines is because you can operate the engine upside down, sideways, hanging off a tree, any way you want. You don’t do that with a snowblower, and you’re not supposed to do that in a car!

I’ve never owned a two stroke snowblower or lawn mower. These would be for wimps. You need higher revs on a chain saw and weed whacked to do the job though. Lots of go karts used two cycle for this reason, but mine was always four cycle anyway.

Some where in my fuzzy memory 2 cycle for chain saws is to reduce weight. Just recycled my 2 cycle snow blower last year! Had a Lawn Boy way back when that was 2 cycle. The go cart we built we used a 2 cycle chain saw engine on.

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Airplanes have to go to some lengths to have the four stroke engines run when inverted, both for fuel and for oil circulation. Often when inverted it’s in a loop or some other maneuver that still results in positive G force.

For chain saws, I’d think it was to run in any position, for weight savings (arms get tired enough!), and for ease of maintenance out in the boonies.


Ah, wet sump crankcase would explained why a four stroke would not run upside down.

Outboard motors were always two stroke until recently to try and reduce emissions. So I still think torque and rpm’s were important, but yeah lots of reasons.

Thinking of that old Scott Atwater though, I think 4 stroke were easier to start and more dependable. Middle of the lake, pull pull pull never leave the dock without oars.

Weight, weight, and weight! 4 stroke can have as much horsepower per displacement, but only at high RPM. The 2 stroke still would have more low end torque. Chainsaws need low end torque! Weed trimmers don’t. They make 4 stroke weed trimmers. I think I tried to run mine upside down when I had one. I don’t recall any problem.

They have made 4 stroke single stage snow throwers but they are too heavy to hang on the wall.

Single stage ones are great at clearing down to the pavement and for up to about 9 inches, but for real work you need a two stage.

A 2 stage with drift bars will easily handle 4 feet. Also you can’t use a single stage on gravel or grass.

I always had both, a 1972, 8hp, 318 cc Airens with a differential that I would not have traded for a brand new one, and a 1998 Toro ccr 2000.

The Airens would throw a solid chute diameter of snow 30 to 35 feet and I used it to make paths all around my back yard for the dog when the snow got over 3 feet. The big one was never in the shop.

:joy: 2 strokes have never had any low end torque. They only have any power at higher rpm’s than a 4 stroke can endure. They just rev up quicker making it seem like the power comes in quicker.


You’re right they need low end torque, but they don’t have it. Chain saws need the power to weight ratio that 4 stokes don’t generally have. This is where 2 strokes excel. But you don’t get the power on the low end (try cutting at idle or about anywhere below half throttle, good luck). Now give that baby some throttle and let it rip. To get higher torque down low is where 4 strokes do better, but most 4 strokes of equal torque and or hp. are too heavy for the average chainsaw user. The there are the electric saws, full torque the moment you pull the trigger. Weed eaters benefit from the high rpm of a 2 stroke or electric, and the weight advantage. 2 strokes are getting better with the low end torque with progress in the intake port valving. Just look up the torque and hp. curves of 2 vs. 4 strokes, the 2 strokes don’t peak until a much higher rpm. I have gone electric for all my lawn equipment all the low end torque of a four stroke and even less weight than the 2 stroke what’s not to like. Well except the charge duration, but hell, I need a break every now and then too. My snow throwers are still 4 stroke I like the low end grunt, and can get everything done on 1 tankful or less.

I’d say it’s power to weight ratio.

There are indeed small 4 stroke engines that are designed to run in any position. Honda makes several models that are commonly used on weed wackers and other equipment. Ryobe and several Chinese companies also make them.

I live down in the Missouri Ozarks where jet boating is popular on the shallow rocky rivers. The new motors are all 4 stroke for air and water emissions but there are still a lot of the old two strokes on the river. I have talked to those who own the jet boats and a lot of the purists prefer the older two strokes. They are simple and can be modified to exceed their rated cc or horsepower to get around legal limitations on certain rivers which I think most of these guys do. There is less mechanical mass to spin up without a valvetrain so the two strokes wind up a lot quicker which the jet boaters like to get up on plane quickly.

The 4 strokes are a lot quieter, especially when not at full throttle. They are also mostly fuel injected and these don’t seem to give as much trouble as the carbs. I mainly kayak but if I got one of these, it would be a 4 stroke. The purists don’t like the new ones because they are all computer controlled and a lot harder to modify for performance.

There were two guys waiting to launch at the boat ramp who were friends. They basically had the same boat but one guy had an older 2 stroke and the other a 4 stroke, both of the same rated horsepower. They said that the two stroke would win out if lightly loaded in terms of speed but that the 4 stroke is way better if heavily loaded.

Certain applications can be adapted to any engine using a different transmission/gearbox ratio.

They also make certain lawn equipment that is technically 4 stroke but runs on a 2 cycle oil mix. This eliminates the need to a complicated lubrication system to account for the machine being operated on its side or upside down. 4-MIX engine: Lightweight with good lugging power | STIHL | STIHL

I have a Toro 4 stroke weed trimmer and I would never go back to a 2 stroke. It powers through thick stemmed weeds at just above idle that would easily stall my previous 2 strokes. It is orders of magnitude quieter and weighs no more than the 2 stroke equivalent. The oil reservoir is on the back side and can keep the engine lubricated in any orientation you can hold it. It must be more than 9 years old by now and shows no signs of loss of performance.

Battery powered equipment, including chainsaws, is taking over. I suspect there won’t be any engines on these tools in the very near future. I have a battery operated limb saw that uses a chainsaw cutter and it works flawlessly as well.


That’s not the same as low end. Low RPM at full throttle is what i mean.

I should have said mid range torque and not low end torque.

2 strokes put out more torque since they fire at every revolution, but at screaming high RPM they lose torque faster than a 4 stroke. So a 4 stroke has to spin very fast to match the 2 stroke. When you start cutting with a chain saw the engine is dragged down to mid range RPM and with a 4 stroke it would lose more power than the 2 stroke would, even with the 2 stroke and 4 stroke having the same rated horsepower.

I was watching an outboard comparison between a 60 HP 2 stroke and a 60 HP 4 stroke. The 2 stroke would always win at getting up to speed faster, but both would perform the same once up to speed. I believe the 2 stroke has more torque at mid range speed than the 4 stroke does. Once both get up to 5000 RPM they are equal. The 2 stroke is 3 cylinder and the 4 stroke is 4 cylinder and it still needs a litte bit more displacement to match the 2 stroke! An extra cylinder and all the other stuff that a 4 stroke needs must increase the weight significantly.

The type of propeller used can also make a big difference. It kind of sounds like the 2 stroke may have had a propeller with more pitch on it. When tuning for performance it’s important to make sure that the boat motors are turning at their optimal speeds. Too much propeller pitch will bring the RPM down and reduce the available engine power. Sometimes someone will put a much larger outboard on their boat and it will actually go slower than before.

I recently bought a battery operated weed wacker. I am very impressed with it. Can’t believe I waited so long to go with a battery unit.

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I’ve got a battery weed whacked and it works fine. Threw the gas one away. Just tired of the maintenance. I did buy a battery pole saw though, a cheap one, and while it works ok for me, the rpm is much much lower than a $600 stihl Gas version. You buy what fits your needs. I think the battery chain saws are better than the electric I bought years ago, but I can run my gas ones all day long and all I need is a tank of gas.

I’ve owned a two stroke mower before. I had a piece of property with steep hill. Couldn’t keep a regular 4 stroke mower alive for a season. 2 stroke engine was the solution.

Honda GX35 engine.

Honda Releases the New GX35 -A 360-degree-inclinable, Ultra-Small 4-Stroke Engine

August 26, 2003, Japan

Power Products

August 26, 2003—Honda Motor Co., Ltd. has announced the release of the new GX35, a 360-degree-inclinable, 4-stroke engine (35.8cc displacement) that will serve as a power source for trimmers and a variety of other handheld power equipment. Honda will also be supplying the engine to other power equipment manufacturers on an OEM basis.

The GX35 features the same lightweight and compact design, 360-degree-inclinability, and outstanding environmental performance as the 25cc-displacement GX25 that debuted in 2002 as the ideal engine for handheld operation, along with powerful output and tenacious torque for improved work efficiency.

The engine’s oil-immersed timing belt OHC configuration makes it possible to incorporate the valve train into the oil reservoir for substantial weight and volume savings. Honda’s original rotary slinger pumping lubrication system ensures full oil lubrication no matter what the engine angle, allowing it to be continuously operated or stored in any position.

The GX35 offers superb environmental performance, achieving a top-class1ranking under US EPA (Environmental Protection Agency) Phase 2 regulations—the most stringent in the world—while achieving a power-to-weight ratio on par with that of a 2-stroke engine. It also delivers an outstanding balance of all-round performance combined with low noise and low vibration, for efficient, carefree operation. The GX35 also clears Japanese domestic Phase 22 voluntary emissions regulations for 2011, and is expected to qualify for Stage 2*3 certification under EU emissions regulations well ahead of the 2007 deadline.

Back in 1955, my dad bought a two stroke LawnBoy mower. The owner’s manual had blow-up diagrams for every part of the engine. It was an easy task to replace the breaker points and condenser, put a new needle and seat in the carburetor, and even replace the piston rings. The cylinder was tapered, so a ring compressor wasn’t needed. I could do any repairs on that engine with simple hand tools. The fuel requirements were a half pint of 30 weight non detergent oil to a gallon of gasoline.
About every 20 hours, the muffler had to be removed and the carbon scraped off the exhaust ports. Also, the spark plug had to be replaced more frequently frequently than a spark plug on a four stroke engine. The deck was magnesium, so with proper care, the mower would last almost forever.
I really liked the simplicity of that two stroke engine and the deck that wouldn’t rust. However, the two stroke engine did pollute more than a four stroke and the cast aluminum or magnesium decks were outlawed because a rock could shatter the deck if kicked up by the revolving blade.


I am sure the pitch of the impeller makes a big difference with boat motors and would assume they are different for a 2 stroke vs 4 stroke. The two stroke is going to do better with an impeller pitched for higher RPMs because that is where the power band is compared to a 4 stroke that reaches its peak at a lower speed. It is like transmission gear rations for slower turning diesel engines vs. gas.