Exhaust Delayed Scavenging

[Chris-PA]

the non strato wildthingys have 1 small air inlet near the flywheel. If the crapsman is the same way then open it up a bit to compensate for the bigger draw from the carb and porting.

Well I think the original airbox entrance is large enough, but I enlarged it a little anyway. Here is the original:


And here enlarged - the setup actually filters quite well and I didn't want to jeopardize that:


The early saws were listed as "Turbo" filtration and had this inverse scoop:


But it was probably a PITA to mold, and you can't take the engine out without removing the flywheel (I remove them with the engine mounted anyway).

 

[bikemike]

Well I think the original airbox entrance is large enough, but I enlarged it a little anyway. Here is the original:
View attachment 492668

And here enlarged - the setup actually filters quite well and I didn't want to jeopardize that:
View attachment 492669

The early saws were listed as "Turbo" filtration and had this inverse scoop:
View attachment 492671

But it was probably a PITA to mold, and you can't take the engine out without removing the flywheel (I remove them with the engine mounted anyway).

J b weld the primer? All 3 bulbs I had went bad. Ran a line from carb to tank and put a ball bearing in the line to block the flow. Seems to work

 

[Chris-PA]

J b weld the primer? All 3 bulbs I had went bad. Ran a line from carb to tank and put a ball bearing in the line to block the flow. Seems to work

That is an older blank and I think that's a fill of Permatex Ultra, but I made one on the 3D printer too for the squish modded saw:


I've just been too lazy to print another.

The 34/64" carbs from the 46cc saws don't have any purge bulb connection, other than that they drop right in, linkage and all (for the A/V saws, not for the solid chassis saws).

 

[LegDeLimber]

Can ya incorporate one of those "circle/slash" designs, imposed over a punch bubble image, into the face of that plug??
Yes, I hate purge bubbles. Just solder shut the hole in the choke plate/shutter
and solder the purge line nipple closed too.
Afterwards, you can toss that punch bubble in the trash where it belongs.

 

[Chris-PA]

Can ya incorporate one of those "circle/slash" designs, imposed over a punch bubble image, into the face of that plug??
Yes, I hate purge bubbles. Just solder shut the hole in the choke plate/shutter
and solder the purge line nipple closed too.
Afterwards, you can toss that punch bubble in the trash where it belongs.

I actually like purge bulbs and wish the larger carb had a fitting for it - I even looked into modifying the carb to add one, but it wasn't worth the effort.

I also considered using that mount as a fitting for something. I will admit that my original intent for this saw was to add a supercharger blower from the cooling fan, and in that case the purge bulb mount was going to become a fitting for a vacuum gauge so I could tell how it was working. But after reading a bit I realized that it wasn't going to work, and that the flywheel fan was not going to be adequate anyway.

If it wasn't in the way of the starter I'd make it into a scrench holder.

 

[heyduke]

I actually like purge bulbs and wish the larger carb had a fitting for it - I even looked into modifying the carb to add one, but it wasn't worth the effort.

I also considered using that mount as a fitting for something. I will admit that my original intent for this saw was to add a supercharger blower from the cooling fan, and in that case the purge bulb mount was going to become a fitting for a vacuum gauge so I could tell how it was working. But after reading a bit I realized that it wasn't going to work, and that the flywheel fan was not going to be adequate anyway.

If it wasn't in the way of the starter I'd make it into a scrench holder.

interesting idea, i've seen some old aircraft engines, rotaries, that have a cooling fan on one side of the flywheel and a supercharger turbine on the other. then there's the detroit diesel, 2 stroke, that uses a supercharger to blow fuel/air into the combustion chamber thru poppet valves instead of crank case pressure and piston porting.

 

[Chris-PA]

interesting idea, i've seen some old aircraft engines, rotaries, that have a cooling fan on one side of the flywheel and a supercharger turbine on the other. then there's the detroit diesel, 2 stroke, that uses a supercharger to blow fuel/air into the combustion chamber thru poppet valves instead of crank case pressure and piston porting.

Just looking at what would be required in terms of a blower it didn't look like the flywheel fan was going to be adequate, or at least as much of it as I could steal given it had to keep functioning as a cooling fan.

Then there is the question of adequate for what? From everything I have read you just cannot force more air into the cylinder on a piston ported 2-stroke without any valves, as the extra charge will just blow out the open exhaust port. You must add some sort of exhaust restriction or exhaust valve to prevent this. And when you compare it to a resonant pipe it just doesn't make sense - the pipe is the exhaust so it achieves the same effect but you don't have to add extra stuff on the exhaust beyond the pipe.

Anyway, my thought here was not really to produce positive pressure, but to improve volumetric efficiency a bit - I had planned to use a combination of 3D printed parts and some tubing. It would have been a fun project but in the end I decided it was not likely to be effective at all.

 

[Chris-PA]

I ran my other squish modded Poulan today, which has the older, smaller combustion chamber and a small pop-up, as well as case inserts - and there really was not much comparison. This saw runs nicely but can't hold a candle to that one. Compression wins.

 

[bikemike]

interesting idea, i've seen some old aircraft engines, rotaries, that have a cooling fan on one side of the flywheel and a supercharger turbine on the other. then there's the detroit diesel, 2 stroke, that uses a supercharger to blow fuel/air into the combustion chamber thru poppet valves instead of crank case pressure and piston porting.

They sounded mean too. Very pissed off

 

[heyduke]

They sounded mean too. Very pissed off

don't be so quick to use the past tense. there are still plenty of detroit diesels working for a living. they're one of the most popular and durable marine engines. and they're used for stationary power. i wish i could toss my ford powerstroke and bolt in a detroit, no more on-board computer, no rube goldberg fuel injection, direct injection controlled by the same cam as the valves. on my powerstroke it takes most of a day's work to change a glow plug. detroit diesels are one of the few things that gm got right.

 

[bikemike]

don't be so quick to use the past tense. there are still plenty of detroit diesels working for a living. they're one of the most popular and durable marine engines. and they're used for stationary power. i wish i could toss my ford powerstroke and bolt in a detroit, no more on-board computer, no rube goldberg fuel injection, direct injection controlled by the same cam as the valves. on my powerstroke it takes most of a day's work to change a glow plug. detroit diesels are one of the few things that gm got right.

I like the 2 stroke Detroit. They have that good old pissed off growl many old jd farm tractors had them too

 

[OldJack]

I like the 2 stroke Detroit. They have that good old pissed off growl many old jd farm tractors had them too

Right colour, wrong make. Oliver 990, 995 and 1900 used a Jimmy 3-71, and the 1950 used a 4-53. I don't recall any John Deere that used a Jimmy beside the rare 8010 and 8020.
http://www.tractordata.com/farm-tractors/000/7/1/711-oliver-1950-engine.html

 

[bikemike]

Right colour, wrong make. Oliver 990, 995 and 1900 used a Jimmy 3-71, and the 1950 used a 4-53. I don't recall any John Deere that used a Jimmy beside the rare 8010 and 8020.
http://www.tractordata.com/farm-tractors/000/7/1/711-oliver-1950-engine.html

I know my old employer had a John deer with the Detroit oil dripper in it. As long as it was dripping oil it was doing just fine lol

 

[bikemike]

Scavenging solved soon. Answer.
If you don't like it. PIPE It

 

[Chris-PA]

Strangely enough, this saw made from parts of various saws I had around, including the lowest performance non-plated version of the engine, has been getting quite a lot of use. I dunno why exactly, it's just a real pleasant saw to run. My other one has more power, but it's a little more finicky too in terms of starting and I keep a longer bar on it. This one is just easy, and it really runs surprisingly well. So far there's not a hint of cylinder wear issues. I've been keeping a 60DL bar on it because I had it around, and I even like that as it is a useful bit longer than the 56DL 16" bars.

Funny how sometimes it's the saws you leave laying around because they're not worth much that you end up grabbing and using and liking.

 

[astnmacgto]

Strangely enough, this saw made from parts of various saws I had around, including the lowest performance non-plated version of the engine, has been getting quite a lot of use. I dunno why exactly, it's just a real pleasant saw to run. My other one has more power, but it's a little more finicky too in terms of starting and I keep a longer bar on it. This one is just easy, and it really runs surprisingly well. So far there's not a hint of cylinder wear issues. I've been keeping a 60DL bar on it because I had it around, and I even like that as it is a useful bit longer than the 56DL 16" bars.

Funny how sometimes it's the saws you leave laying around because they're not worth much that you end up grabbing and using and liking.

Been lurking on this post for a little while, what program do you use to do your cylinder mapping?
ADLM

 

[Chris-PA]

Been lurking on this post for a little while, what program do you use to do your cylinder mapping?
ADLM

Hey sorry I missed this - I did those using AutoSketch because I have a copy, but it's just a generic mech drawing program. Anything that can draw circles and line and rotate by angle will work.

 

[astnmacgto]

Thanks a bunch

 

[Rx7man]

You should be able to do something in Excel that draws the port timing.

Allis Chalmers dozers also had Jimmy diesels, but I like the sound of the Buda engines better

 

[GypsyCliff]

Dang I sure wish I understood more of what y'all are talking about! It's incredibly interesting anyway, but would be even more so if I could understand the terminology.

I Really Want to Learn, just don't know enough to get everything you are saying. Is there a book, or video that explains more in detail making a saw "Hot"?

Great thread anyway!

Cliff