461

[Magnus]

Is it it a fresh air engine or conventional?

 

[Jed]

Kevin: I can't thank you enough for all of those shots. Say... if you get a chance, wld you ever consider showing a shot of your cylinder after you've ported it? Trade secrets, I know, but just curious. Btw. I've got absolutely no idea what the deuce "fresh air engine" means. It was always my impression that those weird extra ports were to channel the exhaust gasses back into the cylinder yet again to "burn it twice" before emitting it out the exhaust port. Am I waaayyy off here????

 

[Cut4fun]

Kevin: I can't thank you enough for all of those shots. Say... if you get a chance, wld you ever consider showing a shot of your cylinder after you've ported it? Trade secrets, I know, but just curious. Btw. I've got absolutely no idea what the deuce "fresh air engine" means. It was always my impression that those weird extra ports were to channel the exhaust gasses back into the cylinder yet again to "burn it twice" before emitting it out the exhaust port. Am I waaayyy off here????

It's not me. It is Randy aka mastermind and he is a member here too (his still pics before porting). One of the videos is Scott treemonkey 461 he is porting for another guy.

 

[Jed]

O.k. thanks Kev. Got it. But was I right about the "extra transfer-port" theory? As far as re-burning the emission gasses goes?

 

[HolmenTree]

I haven't talked to my "buddies " at Stihl yet. My Husqvarna switch is a little awkward
But from lookin at the teardown pics the frontal intake transfer port under the exhaust port branching off into quad tranfers has me thinking of an old dirt bike design.
The "flange" is definately a crankcase stuffer and a some sort of deflecter, ......I can see it offering a much more rigidity for the crankcase. Is it hollow???

It's obvious this almost conventional 2 stroke design didn't cost alot to produce and its keeping EPA happy......
Never under estimate the Stihl force.

 

[SouthSoundTree]

I see now. I thought that it was the magnified 'before' to be followed up by and 'after' port-polishing. Little did I suspect is was an odd colored log and branches. Had it had a 'play' triangle on it, I would have clearly seen what was what.

 

[Magnus]

Btw. I've got absolutely no idea what the deuce "fresh air engine" means. It was always my impression that those weird extra ports were to channel the exhaust gasses back into the cylinder yet again to "burn it twice" before emitting it out the exhaust port. Am I waaayyy off here????

What I call fresh air engines is the type of engine that has a port for air (without fuel) to flush out after combustion and reduce amount of unburnt fuel going out and back in.
These transfers are for letting the gas/air mix up above piston. Not much special. The design has been avoided on saws since the early 50´s. Distance it travels when they are in front like this is longer and to get same speed up over piston, higher speed and pressure is needed from case and up. It also give longer tubes, this add weigh in more metal. The weight talk in designs is unbelievable. The talk about 1/10 of grams for example so the guy who designed this missed that memo...

 

[Al Smith]

In a conventional two cycle engine the "blow down " portion of the transfer is actualy short circuiting a fuel/air mix to purge the cylinder .With this new design it just uses air basically through the front transfer port I believe .

What I think is happening is because with basically no time inside the crankcase to absorb some heat it's colder and thus cools down the combustion chamber a tad bit .As such it seems this design of saw needs a little longer run time at full throttle to gain some momentume as it warms up .

It would make sense though if you stop and think about it that this design would be less polluting .The only reasons really the manufacturers went to this design is because it's mandated by the EPA in the US and what ever governing body it might be other places .

Who knows this design might stay a while or be replaced by something else as time goes on. Just look at how much different the designs on automobile engines have changed in the last 20 years .I mean they certainly are not your fathers Oldsmobile any more .

 

[Magnus]

As I see these pic's, there is only one port in, that is thru carb. No fresh air going in.
This old transfer design is better in many way's, but it is not piston ported, so I don't see why piston is ported....
If there was a meaning to that it would need a lower transfer port were it go thru piston in to transfer and above piston.
That would make it a mix of old conventional transfers and this older type we see, but I can't see it in the pic's.

 

[Magnus]

This makes no sense to me..
http://en.stihl.ca/STIHL-Products/C...chain-saws-for-forestry/22101-130/MS-461.aspx

"2-stroke engine with stratified charge. A fuel-free layer of air is created between the burned charge in the combustion chamber and the fresh charge in the crankcase, reducing the amount of fuel lost during the charge cycle. This results in more power with a lower weight, up to 20% lower fuel consumption than regular 2-stroke engines and significantly reduced exhaust emissions."

Were is the air coming in?
Why is case cut for low ports as well as piston, but there is no in cylinder??

 

[Al Smith]

" Cut for fun " AKA Kevin had a vid clip cad cam deal showing how it works .Evidently it sucks air into the bottom intake ports which do not go through the carb .This air is blocked from going through the crankcase by the piston skirt .When it comes time the piston is going down and transfer would occur it expels this air first before following up with the fuel and air charge that did go through the carb and is now in the crankcase .

I'm not certain if this air takes up the degrees of rotation for normal blowdown or not .I'd guess probabley not before the fuel and air get there .

Now I'm about as much in the dark as you are because that's about all I know about it .I'm sure if a person could really see inside one of those designs it would be pretty clear how they work .Pictures are helpfull but they don't tell the whole story .

Another great mystery would be does the crankcase volume of this design have more or less capacity of a normal chainsaw .I would almost guess less but again that's only speculation .

 

[Magnus]

"Evidently it sucks air into the bottom intake ports"...

From were does it suck the air??

Is this what you mean: http://chainsawrepair.createaforum.com/stihl/stihl-ms461/15/
http://translate.google.com/transla...tsweisender-umweltfreundlichkeit.aspx&act=url

If so, this is not same engine as this clearly have two intakes. One with gas mixed and one fresh...
Not same as this engine posted in this thread...

 

[Magnus]

Nah, this looks to me like a normal engine with front transfers.
I can't see anything special or new other than bracket that is mounted opposite transfers...

 

[Al Smith]

Well since you mentioned it the longer I look at it the more I get confused .From the picture I can only see one set of transfer tunnels coming from the crankcase .Yet at the same time unless it's a reflection it appears to have a tunnel on both sides that would transfer through the windows in the piston just like normal Stihl design would do .

Now could it be that the air blow down is this side tunnel which splits off to each side ?If so what keeps the fuel mixture out of the fresh air blow ? From the pics I can't really see the intake port or ports which ever they are .

Also that's one weird shaped cylinder with it's fins and stepped design in the head deck area .What a great mystery this is turning out to be .

 

[Magnus]

Well since you mentioned it the longer I look at it the more I get confused .From the picture I can only see one set of transfer tunnels coming from the crankcase .Yet at the same time unless it's a reflection it appears to have a tunnel on both sides that would transfer through the windows in the piston just like normal Stihl design would do .

If you look at cylinder base it will not allow any flow as cylinder cover the cut outs that are there in case as for a saw with open ports.
Piston is ported as if it were used for closed ports, so gas air mix go thru it. Here the fumes have no place to go from piston and out as there are no ports there in wall of cylinder.

I would like to know more...

 

[Marc-Antoine]

Is it it a fresh air engine or conventional?

the french one is a fresh air engine, said on the Stihl's site.
http://www.stihl.fr/Produits-STIHL/...pour-travaux-forestiers/22152-131/MS-461.aspx
The cad-pic showed is extracted from the vid.
I agree, it's theoretical and doesn't match with the actual engine. I can't get how it works too.

There must be something we don't see or (and) don't know. (Very deep though, isn't it).

For the piston shape and the cut out in the crank case, couldn't it be parts ready for 2 different versions, one with the separate fresh air intake and one with better flow control like the saw in the pics?
2 possibilities, only 2 molds for the cylinder, and same ref. for the other parts.

 

[Magnus]

It could very well be this saw is meant to have another cylinder in another version or something, but I would still like to know what is what.

I find it really strange that no one can explain...

 

[Marc-Antoine]

Headache coming...

 

[Marc-Antoine]

Couldn't it be a copy-past marketing ( homogeneous series), not followed by the technical staf (EPA compliant enough, with moderate and less costly modifications)?

It isn't a satisfactory explanation, but that's all I have found for the moment.

 

[Cut4fun]

Joe and crew from India running the 461 on the job cutting rubber trees.

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[HolmenTree]

Thanks for posting that Kevin. Very intriguing, man the rubber sap was sure flowing when the one guy whacked the measurement mark on the tree with his machete.

I watched the whole thing waiting for the elephant to come and haul off the logs

 

[woodworkingboy]

Baggy trousers look close, but those fellows need some real chaps. Around here that sort of measuring stick is called a "baka bow", which literally means stupid stick.

 

[Al Smith]

I'd imagine many of us could figure that engine design out if we just had a chance to see inside of one .

In my case it most likely will be years before that happens .

 

[Cut4fun]

here is the before and after porting video's of scott treemonkeys work. Oh CLICK the dang pics to watch video.

 

[HolmenTree]

For it to be a fresh air engine with "good emissions" as they say it needs another intake for fresh air, without fuel.
But I can't figure out were the fresh air come in???

Magnus I can see where the fresh air comes in . Look at the cutout on the base of the exhaust side of the piston. When the piston is TDC the cutout allows intake air through the exhaust port.