Ms461 saw design

[Chris-PA]

That's great and all......but most guys don't have a lathe, the proper tooling, nor right angle handpieces in the ol' toolbox. Unless you consider porting a saw just widening the ports a little.

Without that equipment (and more importantly knowledge & experience) there are things you can do, and things you cannot. And some things you can do, but not as well, not as easily and with more risk of damage. I've had fun modifying some saws, and with some success too, but the ones I work on are not really worth anything financially. And I've wrecked a few cylinders too. Also, some designs are easier to work on (removable transfer covers, etc.). So if you are going to play you should pick your target according to what you plan to do to it, and what you can afford to ruin.

 

[Hedgerow]

Give it a couple turns on the Low side.

Wiff that orange screwdriver....

I'm thinking it's magic. Some Harry Potter stuff going on inside that motor.

I told you it was "The Force" that kept the fresh stuff in there... Stihl bought the rights to it...
But nobody listens...

 

[blsnelling]

Bigger hunk of metal n front on muffler inlet plusa do hicky for cooling in crankcase= Stihl Delayed Stratified Technology!! Crap probably cost me 400$ more

The muffler is the same.

 

[KG441c]

The muffler is the same.

So basically Stihl just made up a big technical lie.

 

[blsnelling]

So basically Stihl just made up a big technical lie.

That's my take on it.

 

[KG441c]

That's my take on it.

thats great for the customer ? why did they add diffuser / stuffer and what advantages does a stuffer in crankcase offer?

 

[blsnelling]

You know as much as I do, reading what's in this thread. I don't design these things, I just mod them until I like the way they run. I don't touch the diffuser.

 

[treeslayer2003]

i agree with Bob in that the 461 will run right with a stock 660.......maybe a tad better. reminds me of an 064.
i know next to nuthing about the tech side of this but flow velocity does make sense to me.........think high rise intake?

 

[Marshy]

thats great for the customer ? why did they add diffuser / stuffer and what advantages does a stuffer in crankcase offer?

Theres a lot to learn about 2 stroke combustion theory, I dont claim to know much of it but it does make for some interesing reading. Stuffers are used to change the primary compression ratio of the crank case which alters how the fuel charge is passed into the cylinder. Just search "primary compression ratio of crank case" and start reading. Just make sure what you read is credible.

"The Crankcase Compression Ratio in a two stroke engine is the ratio of the volume below the piston at TDC (including all of the transfer passages, piston underside volume and intake tract back to what would be the closing item such as reeds, rotary disc or piston skirt plus the crankcase volume with crankshaft installed) divided by the remaining volume in the crankcase with the piston crown edge located at the exact height of the highest transfer port's roof (just before the "break open" point). It is very time consuming to measure and changes with any crankcase modifications, transfer porting, base gasket machining or spacing, reed spacing or rotary valve "tunnel porting"."

Moral of the story and big picture idea with reducing crank case volume is that the maximum volumetric efficiency occurs at higher RPM.

 

[MustangMike]

I was starting to think I would not reach the end of this thread, seemed to be growing as fast as I could read it, and still unresolved issues ... I'm not sure that I can buy that Stihl designed something that does not work, and that the EPA bought it w/o testing, but I am not knowledgeable enough to enter this fray.

On the other hand I know the builders know what works, there is too much feedback out there to deny it, Hmmm....

 

[tree monkey]

so just how mutch pressure do you all think is in the case?

 

[RedFir Down]

All ears Scott.


Just a wild guess from the little bit of sense in my head.... @ working rpm maybe 5-7 psi?

 

[wigglesworth]

so just how mutch pressure do you all think is in the case?

All of it.

 

[windthrown]

Stihl's FI is not direct, they just squirt fuel into the case.

Assuming this system works as described, let's compare it to a piston ported strato. The Stihl delayed scavenging:

1. Uses exhaust backpressure and long transfer timing (although the porters say the timing is not unusual) to delay the fresh fuel charge.
2. The arrival of the entire fresh fuel charge, air and fuel, to the cylinder is delayed so that it does not have time to get across the combustion chamber and out the port before it closes.
3. Using exhaust gases to create the delay means the cylinder and transfers spend a lot of time filled with hot exhaust gas, and a deflector is added to help cool the piston.

Alternatively, for the piston ported strato:

1. No excessive backpressure is needed.
2. The only portion of the fresh charge that is delayed is the small volume of air that carries the fuel - most of the air for the fresh charge has lots of time to get to the combustion chamber and is already there when the fuel arrives.
   
3. The delay of the fuel is caused by cool fresh air drawn through the strato intake and across the piston.

Interesting that Stihl has used this on two designs, one of which has been recalled, apparently for piston problems.......

Yes, not direct fuel injection on the cut-off saw. My bad...

Agreed on your strato saw descriptions, and the way I see this thing working. I also agree that the 661 is likely failing from the added heat. Word that I have from the Midwest is the 661 cylinder is what is failing and being redesigned. My guess would guess a heat sink is being added, or some other method of cooling. It may be the piston as well though. Hard to tell, as Stihl is being very tight lipped about it.

 

[windthrown]

Have you put any time on a 461 yet ? I do not know how they run stock ,but my modded one drinks fuel ,i think the epa stuff is broked or something

I ran one at a local Stihl shop, but I did not put any serious time on it. Only 5 or 6 cookies. It was impressive; the power of the 460 with the vibration of a 440. I sold my 460 b/c of the high vibe, and the 044 with a CDN DP cover was more nimble and had about the same power. I was not so thrilled with the rubber mounts though. I prefer spring mount saws, as I have tendonitis.

As for your modded 461 drinking fuel, it may be that the exhaust scavenging was modified out. Without the exhaust buffer more raw fuel would get dumped into the muffler before the exhaust port closes, which is the same as on pre EPA saws. Then the gas mileage would drop significantly. I would think that if (as seems to be the case) the Mod Gods are just treating these saws the same as pre-EPA saws, they are seriously changing the dynamics of the scavenging flow.

 

[blsnelling]

Windthrown, have you ever ported a saw? Ever degreed one? Have you even read what we've been trying to tell you. The port timing in the 461 is no different than any other traditional 2-stroke saw. Additionally, the muffler is the same as in the 460. Are you now declaring the 460 as a strato saw? You've offered no logic what so ever to support your claim. All you can do is regurgitate the marketing propaganda from Stihl. I've always trusted what you say be fact. I'm not sure what think now.

 

[MustangMike]

Brad, I have a lot of respect for you and Randy, and that you guys can make saws run like they have never run before is not in question. However, I also have a lot of respect for Windthrown and his knowledge base. May I suggest that that we continue the discussion in a mature manner w/o trying to stifle anyone else's point of view?

I enjoy hearing, and seeing the debate, of various perspectives.

Thanks

 

[blsnelling]

Again, show me the real world evidence. Don't just regurgitate Stihl media. No one has done that. If someone can do that...fine.

 

[Mastermind]

Brad, I have a lot of respect for you and Randy, and that you guys can make saws run like they have never run before is not in question. However, I also have a lot of respect for Windthrown and his knowledge base. May I suggest that that we continue the discussion in a mature manner w/o trying to stifle anyone else's point of view?

I enjoy hearing, and seeing the debate, of various perspectives.

Thanks

He just said he's never seen inside of a 461.......what knowledge base are you referring too?

 

[KG441c]

Stratified Technical Bull****!!!!! lol!!