Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

December is here and I'm anxiously waiting for some good snow to arrive.  I've been bit by the 2 cycle bug recently.  I have the Toro 421QE, which is the 4 cycle version of the 221Q.  I thought it may be redundant to pick up a used 221Q so I've been looking into getting a Toro Powerlite.  Plus, I can hang the Powerlite up on a wall.  the 221Q is too big and heavy to do so.

Anyways, anybody got a recommendation for a compact SS two-cycle?  If not, please provide a 7 step sure fire way to cure the 2 cycle habit.  :)

Why are the 2 stroke engines rev so easily without strain?  I've been favoring the 4 stroke engines due to more relaxed RPMs, low end torque, and lower exhaust tone.  However, if these 2 stroke engines are comfortable being rev up, I might change my view on them.  How are the torque curve for a 2 stroke at higher RPMs?

 

>>Why are the 2 stroke engines rev so easily without strain? 

 

   Part of the reason is no cam and valves to move, short stroke, lighter components, power on every stroke,

 

>>However, if these 2 stroke engines are comfortable being rev up

 

   They were designed for that and comfortable.

 

>>How are the torque curve for a 2 stroke at higher RPMs?

  

   Tough to get an engine curve but generally the two strokes fall off very rapidly on the high end but designs place the useable range up there.  A high rev’ing chainsaw, wacker or snowblower can do ok up there but the fall off is into the operating range.  For example it’s no problem do buzz through an 18 inch maple with a chainsaw.

 

  Theoretically 2 and 4 stokes have their advantages and weak points and there are many more considerations than what I mentioned above.  Just how good any machine is depends on the implementation for that specific machine.  On that point Toro has a proven record of spec’ing engines to bodies that can take the rev’s (both).

 

   By far the best second hand machines are Toro’s for age vs wear.  The chances are high the engine is fine (compression wise) other than some minor fix and the same for the bodies.

 

    Murray or MTD machines usually require more work and expense.  Murray machines were more difficult to get parts for and usually required more so I stopped buying those long ago.  Eventually the same for MTD although parts were no problem.  The MTD’s in the 4-5hp range were pretty good and I know a few professional clearers who prefer them.  Their smaller machines are not so great and no match for a Toro.

 

   All engines by Briggs of a cc size are not the same.  Just what a factory orders from Briggs in an 87 or 141 cc engine can vary.  What Toro spec’s are good components..

 

   For a “wall hanger” size SS an excellent choice would be a Powerlite.  They can take the rev’s and bumping their rev spec for short excursions not a big deal.  They’ll toss decent snow 25 feet but crap out quickly in high or wet conditions but they handle an inch or two of soaked slush.  They’re perfect for cleaning up and can be flipped around easily, unlike the more ponderous 2450 and 3650, big difference.  The Powerlite is a scrappy and fun machine to use.

Excellent info Trouts.

The key to two cycle engines being capable of high rpms is the fact that every upward movement is a compression stroke and every downward movement is a power stroke.   On a four stroke, the exhaust stroke is throwing the piston upward with very little resistance compared to a compression stroke.  The piston if flung upward with virtually no pressure on it then rapidly pulled down.  This absence of pressure in both directions isn't a good thing.  It's like a dog running full tilt to the end of it chain then being yanked back just as hard.  The faster a four stroke engine spins, the more stress on the components such as crank, wrist pins, connecting rods and even pistons. 

As far as torque is concerned, I've seldom seen situations that will stall the two cycles any more readily than an equivalent powered four cycle.   The main difference is how the engines respond to heavy loads.  A two cycle tends to work hard and strong to a point and when it's pushed to where it will stall, revs drop rather quickly whereas a four cycle will start to bark, drop some revs then if pushed further, stall out.

I find that if you have any kind of hearing, you can tell when a two cycle engine is happy.  When it's happy it will outperform a four stroke of equivalent displacement and if you spin it up, there's no comparison.  I had about an inch of snow on the driveway this morning so I shoveled it all to one side then went for the old Craftsman SS.   We don't have much snow here and temps have been below zero F. for a couple nights so I want to put as much snow on the front lawn as possible to keep frost penetration to a minimum.   The Craftsman handily threw the snow a good 25 feet or more when I put the revs to it.  The fun factor shouldn't be underestimated either.  It's light, powerful and effective.  Nice combination under all but the most demanding situations.

borat wrote:
That's interesting, I've never heard/considered that perspective, about the piston coming up and changing direction without resistance during the exhaust stroke. I'd offer a mild "counter-argument" that it changes direction just as quickly at it bottoms out during each stroke, also not fighting any pressure. And that aspect remains the same for a 4-stoke or a 2-stroke. One difference I suppose is that the connecting rod is under compression when it changes direction at the bottom of the stroke, whereas it is in tension when doing it at the top of the stroke, for whatever difference that might make (not a whole lot, I'd think). I'd expect that a bigger contributor to the fact that 2-strokes tend to rev higher is that there is no reciprocating valve train to deal with. No valves to float, valve spring tensions to deal with, and less reciprocating mass.

On the note of comparing 2-strokes to 4-strokes at the same displacement, I don't think that's quite a fair comparison. As the 2-stroke fires twice as often, they typically have a higher power/displacement ratio (maybe a 200cc 2-stroke is 6 hp, vs 4 hp for a 200cc 4-stroke, to make up numbers). Comparing engines of the same horsepower or torque would seem more fair. But I have little doubt that you can also rev up the 2-stroke substantially higher than the 4-stroke, when messing with the governor.

Don't take any of this the wrong way. I think 2-strokes are interesting, and just got one that I'll hopefully get to try out this winter. Just having a discussion.

Certainly valve train limits a four stroke engine ability to rev.  Even differences between valve configurations, (flat head, OHV, OHC and DOHC) will have an effect on how well an engine will handle high rpms. 

Without valve trains to consider,  the only things in common with four and two stroke engines is crankshafts, connecting rods, wrist pins, pistons and rings.  Therefore the application of those items need to be understood.  That's why I focused on those components in my explanation.  Two cycle engines can be revved without load to very high rpms and not be subject to the potential damage that is more likely to occur in a four cycle engine.  Spinning a four stroke to extreme rpms without a load can possibly cause connecting rod big ends to go a bit out of round.  At least that used to be the theory.  Two strokes on the other hand have their pistons always on either a power stroke or a compression stroke thus keeping everything under a constant load. 

You ever wonder why two cycle engine cranks are pressed together while four cycle cranks are usually machined from one piece?    

         My Harley 1200 cc (4 cycle)  has a pressed together crankshaft

royster wrote:
Do you know why?

I agree with jrtrebor - the Cr20 is one of the best old 2 stroke toros.  The video posted there is mine.

The powerlite is OK but I like the CR20 much better :-)

borat wrote:

A Harley engine is quite unique , in that the crankshaft consists of basically 2 flywheels with one main bearing sandwiched betweem them., onto which both connecting rods are attached , The  distance  of the main bearing  from the center of the flywheel  determines the length of the stroke, Therefore the crank is made in 3 pieces and pressed together ..  The Harley V-Rod   has the same arrangement but the crank is a one piece forged unit.

royster wrote:
Does it have a single piece roller bearing for the big ends?  Can the connecting rods be removed without taking the crank apart?