4 stroke trimmer

[boraticus]

Originally Posted By: OilNerd
I imagine cost of emissions compliance.


Catalytic converter takes care of that.

As far as two cycles and fuel consumption goes, I'd venture to say that one would have to be using a huge number of machines to see a noticeable difference. These new two cycle engines are pretty easy on fuel.

I still say four strokes in OPE applications is more of a novelty than a necessity.

Two stroke technology is sorely under-rated and misunderstood. Bombardier's line of E-Tec two stroke outboard and snowmobile engines
with electronic fuel injection are marvels of power, reliability and efficiency in a simple and light weigh package. More effort should be made to re-vitalize two stroke technology rather than marginalize it in one of it's most useful applications. Pound for pound, two strokes cannot be beat.

 

[Mamala Bay]

Four strokes on small engines such as hand held are still new compared to two stroke. I'll admit for the number of hours I've had with the Shindaiwa two stroke equipment has been amazing. Shindaiwa parts are expensive but that goes with the turf when purchasing a quality equipment. Presently the 4 stroke engine being used has performed beyond it's expectation. I'm very pleased with it's performance but I do NOT have the amount of hours to conclusively say on long term usage it will live up to the billing of the two stroke I've experience. So far it has performed excellent with about 600 hours of usage. Only time will tell.

The last purchase in 1995 Shindaiwa trimmers averaging 500 hours yearly is still going. And make sure you grease those trimmers because I highly doubt you'll have the equipment to fix it and have a bill that will give you a headache.

 

[OilNerd]

Catalytic converters use platinum. Have you seen platinum prices lately? (near $1,400 / troy oz.)

I agree the BRP's ETEC and other new 2-stroke technologies are great, but I doubt you'll ever see them in a handheld versions due to cost and complexity. (fuel pump, injector, ECM)

I think we're going to have to get used to hybrid 4-strokes and full 4-strokes.

The EPA and CARB SORE (small off-road engine) rules have been hard on the OPE industry and it will only get worse for them. The 2011/2012 rules cut HC and NOx by 80% for non-handheld equipment.

 

[boraticus]

I agree that the technology isn't there for "micro" applications. However, I'd love to see a high performance 750cc two stroke street bike.

Take a look at the beautiful work being done down under:

http://www.twostrokeshop.com/TSS.htm

 

[OilNerd]

Sweet! I'd love the same.

I did enjoy BRP's E-TEC, just for its "in your face" value.

 

[tdi-rick]

The new strato design 2 strokes are increasing in weight quite substantially over their 'dirty' parents, (larger castings to incorporate the stato transfers and often extra throttle bodies) and they often need a cat in the muffler too, so the weight benefit is narrowing.
The four strokes are quieter, with a better spread of torque.
The big problem with OPE two strokes is that they are severely limited on the power/efficiency front by having to make do with using a box muffler, although the new strato designs are much more fuel efficient.
The blast of fresh air before the charge hits the chamber reduces mixture losses out the exhaust by a huge %.

BTW, have a look at the small 25 and 35cc Honda's, beautiful design and typically Honda reliable.
Makita/Dolmar are also producing a nice OPE four stroke.
I was shocked when I saw my first Honda brushcutter, and they are now the brushcutter of choice for the commercial operators around here now. I'm guessing a big plus is no chances of seizing with straight fuelling.

Having said that, I'll stick with my dirty two strokes on my saws, thanks.

 

[mjoekingz28]

Originally Posted By: doitmyself
Are you guys talking about a true 4 stroke engine, or something like what Stihl has, called a "4 Mix" engine? It is a 4 stroke with valves, but it still uses a gas/oil fuel mixture for lubrication.

"The revolutionary STIHL 4-MIX® engine is the first mixture-lubricated 4-stroke engine from STIHL and combines the advantages of 2-stroke and 4-stroke engines in a single unit. Unlike conventional 4-stroke engines, which require separate systems for the fuel supply and engine lubrication, the new STIHL 4-MIX® engine is fuelled with the new 4-MIX® fuel mixture."

http://www.stihl.com/isapi/default.asp?c...mix/default.htm


These trimmers are awesome. I used to use them for hours a day and whoever got the 4mix was the lucky guy for the day. Much more torque, barely weigh any more and if you get it you almost have to have the neckstrap for it, otherwise it is practically unusable. The high power motor combined with the handlebars make it a cakewalk to use. If my yard was small enough, I'd just use it exclusively since you can 'mow' pretty accurately with it in a side to side motion. Get the strap just right and you can lean back a little with it and relax a little. Whereas the 2 stroke model didn't have the bars and you have to hunch over somewhat to use it.

When we first started using them, it was easily noticed that they sounded like a 4 stroke but use premix. Never understood that part though.

 

[boraticus]

"but use premix. Never understood that part though."

Premix is required because they don't carry oil in a crank case sump or a dry sump. They use the lubricant mix the fuel the same way two strokes do by pulling the incoming charge of fuel/air mixture through a port(s) into the crank case then drawn up to the intake valve through a transfer port to be pulled into the combustion chamber.

The main difference is that the fuel charge is fully contained in the cylinder once the valves close. On a two cycle, the fuel charge is pulled into the cylinder by negative pressure caused by the downward motion of the piston as well as positive pressure created in the crank case by same piston movement. As the charge fills the cylinder, a portion of the fresh charge goes out through the exhaust port. If the engine has a well designed expansion chamber attached to the exhaust port, virtually all of the fresh charge that had escaped through the exhaust port will meet sufficient back pressure to force the fresh charge overflow back into the cylinder to be burnt with the rest of the fuel. A well designed expansion chamber will go a long way to increase power as well as minimize loss of unburnt fuel being cycled through the system. I've got performance pipes on a couple old two stroke Yamahas. The difference is amazing.