crmyers
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Porting 101
- Thread starter pepsifreak28
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Terry Syd
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Symetry of flow
I don't recall anyone mentioning it in this thread, but one of the most important aspects of porting a two-stroke is symetry of the flow.
I use tracings of the port windows to keep the ports the same and to align the exhaust port with the centerline of the cylinder. If you place a piece of paper inside the cylinder and use a soft pencil (I use a broad carpenters pencil) you can trace the outline of the ports and their relationship to each other.
From the tracings you can measure from the side of the exhaust port to the side of the nearest transfer port. You want to get that distance the same on both sides of the cylinder. Use a set of calipers to measure the distance as you want it as exact as possible.
Likewise, after you do a bit of work you can trace the exhaust port to see if the window is symetrical.
After you get the engine back together again and have run it for a while, you can check the symetry of the flow by looking at the carbon deposits on the top of the piston. If you notice some difference between the two sides, you can go back into the jug and take a look to see what may be causing the difference.
If you never get an exactly perfect pattern, you won't be alone, I've never been able to get it perfect either.
I don't recall anyone mentioning it in this thread, but one of the most important aspects of porting a two-stroke is symetry of the flow.
I use tracings of the port windows to keep the ports the same and to align the exhaust port with the centerline of the cylinder. If you place a piece of paper inside the cylinder and use a soft pencil (I use a broad carpenters pencil) you can trace the outline of the ports and their relationship to each other.
From the tracings you can measure from the side of the exhaust port to the side of the nearest transfer port. You want to get that distance the same on both sides of the cylinder. Use a set of calipers to measure the distance as you want it as exact as possible.
Likewise, after you do a bit of work you can trace the exhaust port to see if the window is symetrical.
After you get the engine back together again and have run it for a while, you can check the symetry of the flow by looking at the carbon deposits on the top of the piston. If you notice some difference between the two sides, you can go back into the jug and take a look to see what may be causing the difference.
If you never get an exactly perfect pattern, you won't be alone, I've never been able to get it perfect either.
TraditionalTool
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All I can say is, WOW, cutting off those tab limiters on the carb helped me to get it running pretty well by just ensuring the screws were out 1 1/4 turns.
Idles much better and seems to run pretty good, but still need to get it dialed in.
Wow, what a great little saw for my $55 investment. It has some roar to it, most certainly...
SWE#Kipp
Addicted to ArboristSite
Here are two pics of my first attempt of porting, have only played with the intake and exhaust.
No bevel made on those pics ,,,
So does it look ok, it's just going to be a work saw and it's still waiting for a pop up and lowering of the cyl !
help and advise will be taken gladly
No bevel made on those pics ,,,
So does it look ok, it's just going to be a work saw and it's still waiting for a pop up and lowering of the cyl !
help and advise will be taken gladly
AUSSIE1
Al.
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Nice and neat.
I keep the walls straight with no radius (from the inside out).
Sides a bit squarer (without people thinking I mean a square port!).
Are you going by the 65-70% of cyl rule?
I've noticed the base gasket is a good fit on the crankcase so I match to cyl/transfers to the gasket.
I keep the walls straight with no radius (from the inside out).
Sides a bit squarer (without people thinking I mean a square port!).
Are you going by the 65-70% of cyl rule?
I've noticed the base gasket is a good fit on the crankcase so I match to cyl/transfers to the gasket.
Looking real good, especially for your first one. +1 on making the walls straight, from flange to cylinder wall.
I finally have some time to start porting the cylinder super sent me. Thanks again and sorry it took so long for me to do anything with it.
Its a 46mm, and i took some pictures...
So i do 46 x 60-70% on the exhaust and put tape inside to know where to grind to.
46x65%=29.9
46x70%=32.2
is this rite?
I don't know what saw it was on and don't know how big to make the intake.
Their is small bevels on it now but after i widen they should be bigger rite?
I'm in the proses of rereading the thread for the 3rd time so i will probably find my answers.
Its a 46mm, and i took some pictures...
So i do 46 x 60-70% on the exhaust and put tape inside to know where to grind to.
46x65%=29.9
46x70%=32.2
is this rite?
I don't know what saw it was on and don't know how big to make the intake.
Their is small bevels on it now but after i widen they should be bigger rite?
I'm in the proses of rereading the thread for the 3rd time so i will probably find my answers.
You'll need the piston to know how wide the skirts are and where the ring ends are.
hmm, i figured but i don't have one....maybe ill just practice grinding on it and port my 028...
You might be able to see where the skirts are from the wear marks in the cylinder.
Very insightful information!
pepsifreak28 and blsnelling Brad - Great information! I thought I knew but now I actually do know! :yourock:
I will be receiving a second cylinder for my 029 super by the end of this week and I am going to attempt on these what you consider "smaller things" and are still pretty big for a newbie like myself.
I will take all the things I have read into consideration and will have to post pics of course, if I hadn't read this I would have probably butchered it haha
Just one question though lets say I polished everything similar to porting and polishing a car or truck heads. Is it actually beneficial to polish these little two strokes or since it's such a small scale polishing doesn't matter? I would thing it would be beneficial but I figured I'd ask anyhow cause smooth surfaces allow more efficient are transfer.
:deadhorse:
-Mike
pepsifreak28 and blsnelling Brad - Great information! I thought I knew but now I actually do know! :yourock:
I will be receiving a second cylinder for my 029 super by the end of this week and I am going to attempt on these what you consider "smaller things" and are still pretty big for a newbie like myself.
I will take all the things I have read into consideration and will have to post pics of course, if I hadn't read this I would have probably butchered it haha
Just one question though lets say I polished everything similar to porting and polishing a car or truck heads. Is it actually beneficial to polish these little two strokes or since it's such a small scale polishing doesn't matter? I would thing it would be beneficial but I figured I'd ask anyhow cause smooth surfaces allow more efficient are transfer.
:deadhorse:
-Mike
Last edited:
Polished on the exhaust side is fine. On the intake, leave it semi rough. I leave the finish my carbide burr makes.
Ok just to clarify I shouldn't mess with what I have marked as #1 since I am new because this changing the timing on this particular cylinder right?
On #2 That's what you were talkin about making 70% of the bore width as long as the clip edges aren't there to catch on the edges
On #3 After I make the width change I then bevel the top and bottom lip a little to insure the rings don't catch
and I can do this to both the exhaust and intake ports or only the inside on the intake and the outside on the exhaust and muffler?
If this is incorrect pls correct me XD
JeremyFXDWG
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First off I stole this picture from Timberwolf's post earlier in the thread. If that is a problem please let me know and I will take it down ASAP.
The question is in reference to the shoddy "bevel" on the newer factory stihl jugs. When we talk about not changing the port timing I am assuming we are talking about the blue line in the photo. When one ports a jug like this can you remove material from the roof / floor of the port to move the red line toward the blue line till a "normal" bevel is archived basically increasing the interior size of the port past that huge bevel?
The question is in reference to the shoddy "bevel" on the newer factory stihl jugs. When we talk about not changing the port timing I am assuming we are talking about the blue line in the photo. When one ports a jug like this can you remove material from the roof / floor of the port to move the red line toward the blue line till a "normal" bevel is archived basically increasing the interior size of the port past that huge bevel?
AUSSIE1
Al.
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Only do the roof of the exhaust and floor of the inlet.
Leave just a very slight bevel. You don't need much.
A large bevel acts a bit like increased timing anyway.
Leave just a very slight bevel. You don't need much.
A large bevel acts a bit like increased timing anyway.
didn't want to start a new thread to ask one question so here goes. When you widen the exhaust you remove the nikasil on the edge, does this expose the aluminum to more wear than an unported jug or risk the chance of the nikasil flaking off the bore?
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