Part One: The Exhaust Port

[lauren]

Has anybody ever tried this?

 

[Moparmyway]

I’d get some sort of snubber on that

 

[Fairways_and_Greens]

Using what Andre was doing on the 346XP that beat all of our asses at Wigg's GTG several years ago........and the heights of some of my stronger running 90cc saws, I arrived at a EX height to CC scale sorta thing.

Now......there are exceptions, so remember this ain't "the gospel". lol

50cc - 105°
60cc - 103°
70cc - 101°
90cc - 100°
120cc - 98°

The biggest exceptions to this "rule" for me are the stroker or over square type engines. They get "different".

Would that put an MS241 at about 106° or 107° Randy?

 

[Mastermind]

Would that put an MS241 at about 106° or 107° Randy?

Pretty much dead on. Of course there are exceptions.

 

[Fairways_and_Greens]

Pretty much dead on. Of course there are exceptions.

Danke, head ape.

 

[Fairways_and_Greens]

So in taking @Mastermind 's video in setting up a homemade wheel attached to flywheel, I came up with something like this:


Going up to 106° get's me to .735 to the squish.


So according to the rule of thumb of 65% to 70% of the 1.67 inch piston, I can cut up to that cardboard and 1.085" - 1.169" wide?


Last question: does just blending to to the exhaust gasket size look good or do I need to go wider?

 

[Deets066]

So in taking @Mastermind 's video in setting up a homemade wheel attached to flywheel, I came up with something like this:
View attachment 158127

Going up to 106° get's me to .735 to the squish.
View attachment 158129

So according to the rule of thumb of 65% to 70% of the 1.67 inch piston, I can cut up to that cardboard and 1.085" - 1.169" wide?


Last question: does just blending to to the exhaust gasket size look good or do I need to go wider?
View attachment 158128

You sure you measured right?
If you raise your port up to that cardboard, I find it hard to believe your gunna be at 106

 

[Deets066]

Looks like a 1/4” at least, maybe it’s just the picture

 

[Fairways_and_Greens]

You sure you measured right?
If you raise your port up to that cardboard, I find it hard to believe your gunna be at 106

You’re totally right. I was at 96. Too many snow caps.

 

[Mastermind]

Be careful widening that much. Double check to be sure you have enough material in the flange.

 

[Fairways_and_Greens]

Be careful widening that much. Double check to be sure you have enough material in the flange.

Flange on the cylinder or piston? The piston flange is GIRTHY.

 

[Fairways_and_Greens]

Looks like a 1/4” at least, maybe it’s just the picture

Thanks for the heads up. This is the real 106.

 

[Fairways_and_Greens]

Be careful widening that much. Double check to be sure you have enough material in the flange.

When you say flange, are you referring to the piston? It seems like I have room for days there.

 

[mdavlee]

When you say flange, are you referring to the piston? It seems like I have room for days there.
View attachment 158204

Muffler

 

[XP_Slinger]

When you say flange, are you referring to the piston? It seems like I have room for days there.
View attachment 158204

He meant the muffler mounting flange. If you widen the exhaust to 70%, you will want to widen the entire port to the same width all the way out to the flange.

Piston skirt width is another consideration when widening the exhaust. But as you said, it looks like you’ve got plenty of room there.

 

[Mastermind]

I'm talking about thru the outlet in the jug. Widen it too much, and you cut a hole.....

 

[Fairways_and_Greens]

He meant the muffler mounting flange. If you widen the exhaust to 70%, you will want to widen the entire port to the same width all the way out to the flange.

Piston skirt width is another consideration when widening the exhaust. But as you said, it looks like you’ve got plenty of room there.

Interesting Slinger, you got me thinking, so I tried my best to trace out the current configuration. I didn't do a great job with scissors (bad sign).

Right now the cylinder side of the port is a touch wider than muffler side. Also, the area between the two appears to be at a ratio of 2:1. Is that a good rule of thumb to maintain?

Do you recommend keeping the widths the same throughout the port Slinger?

 

[Fairways_and_Greens]

I'm talking about thru the outlet in the jug. Widen it too much, and you cut a hole.....

I see what you're saying now Randy, looking at the port casting from underneath. Thanks for slowing me down and leaving me bread crumbs.

Regarding the flange. My thought was to just match the muffler gasket.

 

[XP_Slinger]

Interesting Slinger, you got me thinking, so I tried my best to trace out the current configuration. I didn't do a great job with scissors (bad sign).

Right now the cylinder side of the port is a touch wider than muffler side. Also, the area between the two appears to be at a ratio of 2:1. Is that a good rule of thumb to maintain?

Do you recommend keeping the widths the same throughout the port Slinger?
View attachment 158259

Yes that’s what I like to do. That’s why I don’t always go right to 70% of bore for width. I don’t see the point in widening the port window that far if there will be obstructions on the sides. But I’m still learning too bud, so please don’t take what I say as gospel.

 

[Fairways_and_Greens]

Yes that’s what I like to do. That’s why I don’t always go right to 70% of bore for width. I don’t see the point in widening the port window that far if there will be obstructions on the sides. But I’m still learning too bud, so please don’t take what I say as gospel.

Hey Slinger. I'm like a blind man in an orgy right now. I appreciate the help. You're getting me to think about stuff I wasn't previously.

I think I'm going to try what Randy said re: look at that the saw designer did and go from there, so I think I'm going to try to retain the shape/ratio while creeping up to the timing.

I think I have a plan and am just delaying at this point. Worst case is I screw up the saw and send it to a professional!