Four Strokes Replacing Two Strokes

[TonyM]

This topic came up on another thread, and I thought it worthy of its own. Does anyone think that four strokes will ever replace two strokes, especially in chain saws? I would have never thought four stroke dirt bikes would be so prevelant, but Yamaha changed the equation by making a competitive four stroke motocross bike in '98. KTM further raised the bar, and now for 2002 Honda has an awesome machine. I hear that Yamaha has quite an impressive four stroke snowmobile in the works as well. As the owner of a '98 Yamaha WR400, here's my two cents. In motorcycle racing the rules are set up to encourage development of four strokes by allowing four strokes a 2:1 displacement advantage over their two stroke couterparts. The four strokes are competitive as such, but the penality seems to still be weight. The gap however, is narrowing. My WR400 is about 42Hp @10,000 Rpm and 400cc's. That is about .1Hp/cc using a water cooled five valve engine. I would say the engine alone (not transmission and radiators) weighs around 60lbs (about .15 lbs/cc). Let say detuned to be air cooled it could make .08Hp/cc. To have a 6Hp saw (Stihl 046), you would need 75cc's (6/.08) and 11.25lbs (75*.15). Add some plastic, an oiler, controls, AV mounts, clutch, bar mount, and tanks and you may stay around 14-15lbs. The other question is can it all be packaged ergonomically and sold economically (physically larger engine with lots of magnesium, titanium, aluminum, and engineering). I wouldn't be surprised to see someone like Honda making thier way into four stroke chain saws.

 

[tony marks]

im not an authority and sure i dont have to tell u that.
but seems to me oil required to keep the motor cool enough
would be a big factor against it. just mine .later now

 

[TonyM]

My bike uses about 1-1/2 quarts of oil, but it's carried in the frame using a dry sump system. Oil changes need to occur frequently with that little of oil (especially when it's being used in the tranny too). Cooling would be an issue, as these high compression four strokes do run hot (my header glows red after only a few minutes at idle). Also, how do you keep the oil flowing with something needing to be used in any position?

 

[chainsawworld]

we had a guy come into the shop a while back that must have thought saws were already four stroke. the brand new saw was seized, i asked he put gas and oil in the saw. he replied yes, oil in the oil tank and gas in the gas tank. sure enough, no mix. that poor craftsman saw. believe it or not, that was not the only funny story we repeat around here. gotta love it. protect yourselves; marty

 

[tree monkey]

stihl and shindaowa are both building a new 2 stroke-4 stroke engine. should see them in trimmers in about a year or less. it's a 4
stroke that runs on mixed gas. no oil in crankcase. i think we will see this in saws in a few years.

later scott

 

[TonyM]

How do these four stroke engines running on premix lubricate the bottom end? I remember seeing an interesting engine design on the Web. It was essentially a two stroke piston combined with a four stroke piston running opposed to each other in the same bore. Very strange. I think it had an impressive power to displacement ratio, but I don't think it was being designed for hand held outdoor power equipment.

 

[Cicero]

Will most likely never see four stroke chainsaws because of the rpms that they run and the cooling it requires. Trimmers, blowers, and edgers yes...aprox 8K rpms. Chainsaw at 12K+ will not have a feasible way to cool them. Stihls four stroke engine is actually available in Calif. this spring and Shindaiwa everywhere.

 

[TonyM]

http://www.ryobioutdoor.com/4cycle/pr_3.html

I thought I'd remembered this from an engineering magazine a few years ago, so I did a search. Check it out. Haven't heard much since, so maybe as wasn't as successful as they'd hoped. First four stroke chainsaw? Hmm, that's like saying Yamaha's YZ400 was the first four stroke motorcycle. Maybe first modern four stroke chainsaw.

 

[tony marks]

my son has that 4 cycle trimmer. he bragged a little at first
but i think, not as pleased now. i just dont like the bulky look of it,myself.also cant see this thing in say 50 cc size an turning 12000 . it would be bigger than the 088 and id be afraid if it blew ,it mite take your head with it. just mine. later now

 

[chainsawworld]

didn't kabota have a little diesel trimmer years ago? if i recall, you turned a crank handle that would wind a spring than when you tripped another lever the spring would spin the motor over. marty

 

[TonyM]

I don't think RPM's is the problem, if the engine is designed with it in mind. My motorcycle will hit 11,000 RPM (400cc single). The Japanese sport bikes have been hitting 12-14,000 RPM's for years, and that's at 600cc. Indy cars hit more than that. The trend seems to be heading towards short stroke high RPM engines. The rest of the consideration then needs to be in light weight valves and valve train so that valves don't float at those speeds. That's where the titanium comes into play. Besides, with the added torque from a four stroke, a saw may not need to hit 12,000 RPM's. Just add a couple of teeth to the drive sprocket to get the chain speed up. Size is definitely a concern. I would say that the current motorcycle engines are 25-30% larger than a two stroke with the same displacement.

 

[McC]

Snowmobiles are under emissions attack as well. Yamaha just released the RX-1. They took a 4 cyl. 4 stroke superbike engine producing 150 hp and put it in a sled. The extra torque is said to best 800cc 2-strokes by 65%. It weighs only 5% more than comparable 2-strokes. It is expensive though.

 

[tree monkey]

50 tears ago, if tou told a manufacture that there would be a production saw that would run 15,000 rpm and weigh 15 pounds thay would have put you in a rubber room.

i don't think anyone has a saw that passes the 2005 epa standards ( i could be wrong ). i also believe that the epa standards get even tighter in 2010.

i think there will be big changes in the chainsaw industry in the near future.


later scott

 

[Methoss084]

In 2005 your gonna see a lot of interesting new handheld products out there. While I feel the EPA and CARB ratings for the future are a bit stringent, it also forces the industry to excell and produce new and inovative ways to keep emissions down and performace up. I look foward to seeing whats gonna be next. But I still hate those freakin limiter caps!

 

[sawracr]

It is interesting the way they build the four stroke mix fuel engines, by using a combination of overhead valves and a reed they are able to run the mix thru the crankcase and then into the engine, Stihl on the other hand is keeping the internals of there system under raps. Question : will we see a four stroke chain saw ? Answer: no doubt. Don't worry about RPMs , thats why they make geers, but just think we will be able to mess with cams and reeds, for more power. TECHNOLOGY IS GOOD.

 

[Dagger]

4 strokes

Here are some thoughts:
Calif legeslators have alloted no enforcement authority for the CARB rules, as the board was/is basically just a group of politically correct appointees. These rules are also only for the sales of products in calif. The previous administration in the US is not as suseptable to influence from the left coast, and we have seen a marked drop in pressure as to the advancement of tighter rules to this effect within the EPA, which does have allotted enforcement athourity across the US. However there ability to effect any rules is pretty well limited to making the manufacturers comply, if you dont believe this, then call the local sherrif where ever you are and complain of Joes small engine and saw shop busting the limiters off your CARB approved machine! OR that Home-depot is selling a imported-non-approved piece of equipment and you want it stopped!
Id luv to know what the Sherrif will say! (unless your in calif)
AS far as the 4-stroke development is concerned, Ive read all of the above posts and I believe you all have it pretty well right concerning the discussions of the weight detriments for 4 strokes, and they always will be unless we suddenly see 2 stroke
technology ceasing to advance. Yes the 4 strokes are getting lighter, but the 2 strokes are also!
never-the-less, there is a VERY large cost advantage to the 2 cycle designs in that they require so much less manufacturing resources, and any 4 stroke that can be made competitive in design will cost 2 or 3 times as much.
Honda has the most advanced 4 cycle small engine designs THAT HAVE BEEN SUCCESSFUL on the market and one teardown of any of these engines will tell even the average wrench that the product is apparantly being subsidized price wise by other marketable products.
Still, considering HONDA's fear of litigation, and track record of abandoning markets on the slightest hint of high litigation rates, I doubt that we will ever see them in this biz. ( I use the abandonment of the Snowmobile market in the 70's after many shipments had reached our shores, and then scrapping the new and revolutionary product, a CB750K3 powered sled, and the aviation engine market after investing zillions in research and even a state of the art engine test cell/wind tunnel facilities in the USA, and subsequently just giving it to the university where it was located.)

In summary I believe it is the political climate that has drivin the air quality regulations to the point there are, and that changed dramatically last year. further development in this area will be markedly slower until it gets more politcal fuel!

But Im still awaiting new tec 4 strokes as impaitiently as any one with a wrench for a heart!

 

[Dagger]

OOPS

in the second sentence..read that CURRENT administration ..whew! sorry!

 

[manofstihl]

The stihl engine is based on technology developed for aircraft engines, rpms are not a problem in my opinion. It has 8 more moving parts and weighs only .6 lb more than 2 stroke. Also, the rpms on the fs100 are 11000 I believe. It is available evetywhere (us) next spring.