Cylinder Porting for Dummies....

teacherman

teacherman

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I have followed with interest the various threads on porting saws to improve performance. I am still scared to tackle it, because I don't really know what to do. I know that widening ports is a start, but raising and lowering teh intake and exhaust timing, and the transfers, well, I don't git it. I used to be a professional sculptor, and I have used mini die grinders and the like on stone for years. Would anybody feel like posting a basic how-to that breaks it down in terms that are easy to understand, a tutorial, if you will? I think it would make a great sticky thread, butt that is JMO

Yes, I have searched, and I guess I am in the Special Ed class when it comes to porting. Many thanks.

I have an extra 026 I can practice on, and a 10 lb. orange and white screamer would be cool to have out in the woods on firewood day.
 
7oaks

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I have followed with interest the various threads on porting saws to improve performance. I am still scared to tackle it, because I don't really know what to do. I know that widening ports is a start, but raising and lowering teh intake and exhaust timing, and the transfers, well, I don't git it. I used to be a professional sculptor, and I have used mini die grinders and the like on stone for years. Would anybody feel like posting a basic how-to that breaks it down in terms that are easy to understand, a tutorial, if you will? I think it would make a great sticky thread, butt that is JMO

Yes, I have searched, and I guess I am in the Special Ed class when it comes to porting. Many thanks.

I have an extra 026 I can practice on, and a 10 lb. orange and white screamer would be cool to have out in the woods on firewood day.

+1 from me...Carl
 
teacherman

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I guess I am just slow. I see the pics, I see the ovals drawn on pistons, but I don't see how to configure the ports, where to grind. When you talk about timing, I dont know if you grind on the top or the bottom of the port, and I stihl have no idea whatsoever to do on the transfers. Maybe I am just challenged on the written descriptions, thus the thread title. Step by step how-tos are a pain in the bu††ox to put together, if they really explain it to dummies.

A big concern for me is the nikasil coating and the bevel.. I imagine the bevel was there before the coating was applied, and any port expansion inside the cylinder means the coating is ground off the bevel, and there seems to be a risk of the piston ring peeling the coating, because the bevel you cut when porting will have no nikasil on it.
 
blsnelling

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I guess I am just slow. I see the pics, I see the ovals drawn on pistons, but I don't see how to configure the ports, where to grind. When you talk about timing, I dont know if you grind on the top or the bottom of the port, and I stihl have no idea whatsoever to do on the transfers. Maybe I am just challenged on the written descriptions, thus the thread title. Step by step how-tos are a pain in the bu††ox to put together, if they really explain it to dummies.

A big concern for me is the nikasil coating and the bevel.. I imagine the bevel was there before the coating was applied, and any port expansion inside the cylinder means the coating is ground off the bevel, and there seems to be a risk of the piston ring peeling the coating, because the bevel you cut when porting will have no nikasil on it.

I actually talk about most of that stuff in that thread. The only way to learn is to get in there and start doing it. It'll start to make sense once you have the cylinder in your hand and reread the thread.

Here's what I recommend for starters.

Don't do anything to the transfers, period. You can make tremendous gains without modding them.

Do not raise or lower the intake or exhaust ports. Widen them only. Mark the ports on the piston skirt and then widen them so that there's only about 1/16" left to seal the port. DON'T go any farther though. Keep in mind you have to rebevel the port too. You also have to watch out for where the ring ends are. They are often right at the edges of the port. In that case you may not be able to go as close to the edge of the skirt. You MUST leave cylinder wall for the rign to ride on as it goes past the port window! I wouldn't leave less than 1/8".

Remove the casting lines from the windows in the piston. Also angle them on the inside as I have shown in the 361BB porting thread.

Don't make the roof or floor of the ports too flat. The flatter they are, the more area you open the fastest. But go too flat and you're likely to catch a ring even after beveling.

Make the walls of the ports straight up and down. If you leave them curved, you're not opening the port area as qickly as possible at a given point in the rotation of the crank. You want maximum area as soon as possible. A totally square port would be the max but won't work as described above. It's a balancing act.

Use a round stone to rebevel the ports. You don't need a huge angle. It only needs to be a few thousanths deep. The ring doesn't go into the port window that far. Just lightly round off the edges of the port so that the ring won't catch on it.

Reassemble the engine using a gasket made of any paper or soft metal that will give you a squish of about .020". I've used get well card, pop can cases, etc.. Make sure to use a fuel resistant sealer like Threebond 1104/1194.

A little about port timing. Port timing on the exhaust port is measured off of the roof, closest to the combustion chamber. The critical point is where the port window first opens as it travels from TDC. Do not lower the floor. You may have the port open with the piston at TDC. That's not desireable and lowering it will give you no performance gains.

Intake timing is measured from the floor of the port. That's why some "port" the intake by removing material from the bottom of the skirt of the piston. It's best to lower the port when needed. Again, you don't need to do this on your first saw. Do not raise the roof or the rings may drop below the top of the port and catch. Some actually drop below by design, but there's no gain to be had by raising the roof of the intake.

Correct me where I may be wrong guys. I've only been doing this a couple years.
 
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teacherman

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Thanks, Brad. I do appreciate it. I still don't quite get teh numbers you post for the degrees of rotation on that thread. Is 0˚ TDC, and all the numbers are after or before TDC, or is there another reference point?
 
Lakeside53

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Good write up Brad...

I differ on one small point - don't just use "anything" for a gasket. A gasket must not compress over time or (particularly on bigger saws) you'll end up with loose cylinder bolts and maybe cracked cylinders. Sure, almost anything will work for some period of time, but will it last?

If you have to use paper (verses a coated metal gasket), use real gasket material.
 
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blsnelling

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I hear you Andy. I know that was a problem with the old paper gaskets Stihl used to use and is likely why they now use coated metal. Blown out paper gaskets probably led to the demise of more than one saw. I actually used a paper grocery bag on my 084. I need about .008 and that fit the bill. I'm sure I would be well advised to check to make sure they're still tight after a while. Probably right now after the first few heat cycles would be a good time.
 
7sleeper

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.....Correct me where I may be wrong guys. I've only been doing this a couple years.

your all wrong! ;)




just kiddin

I wish I only knew what you wright about!

greetings from Austria (& from work another 24hr shift :( )

7sleeper
 
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blsnelling

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You can learn it too. It's just picked up from reading here and elsewhere, doing some work, posting lots of pictures and getting feedback, making changes, etc.. It's an evolutionary thing. I'm just now starting to play around a little more with port timing numbers and working on the transfers a litte more. There's a whole science to this madness that's way over my head. I don't understand all the 2-stoke theory, but have a steady even hand and improve on what's already there.
 
Tree Sling'r

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I would not even worry about squish and gaskets at this point, just get a concept of porting.
Leave your squish and gasket the way it is, that way you are not stressing over port timing, which is way over blown at this point.
Get your gains like Brad stated, from widening your ports. Even if you knock the coating off of the ports and smooth it up it will run better.

A basic mod:

Widen the exhaust, raise it by knocking off the coating, smooth it out.

Widen, and lower the intake by knocking off the lip, then leave it rough, but even of course.

Take and remove the lip from the lower transfers so that by feeling it and looking at it, it will obviously flow better.

Just by comparing the before and after - you want better flow and smoothness of the ports.

Don't get crazy, a little goes a long ways.

A porting tool with a abrassive bit will knock off the coating. Once the cotaing is knocked off you can use a round rasp and a chainsaw file on the aluminum with amazing results.

Bevel the ports with a lapradory needle file or a grit stone ball, smoth out with sandpaper, what ever. I use a ball, needle file, then a hone.
 
blsnelling

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I would not even worry about squish and gaskets at this point, just get a concept of porting.
Leave your squish and gasket the way it is, that way you are not stressing over port timing, which is way over blown at this point.

Excellent advise for a beginner. Most of the gains are found in flow improvments rather than compression increases. I think Tree Sling'r ports with an emphasis on torque as well. All those RPMs won't help you if you can't maintain them in the cut.
 
blsnelling

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In all seriousness, you won't learn until you do it yourself. At least that's the way I am. I have to lear hands on. Start with a saw that isn't so expensive. A 260 isn't cheap but it's a lot cheaper than a 660 or 084. I use my 260 as my test bed. I'll try things on it before I will my other saws. Post up your work and let us look at it. We'll try to steer you in the right direction. It's a lot easier if you post the pics in the forum here. That way you get more input and a more balanced approach. We all do things a little differently and can learn from each other.
 
teacherman

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I'll get started at some point and definitely post pics. This weekend I have to start a huge hollow tree removal in my yard, it will be a lot of roping down over houses and such. I know my AC bill will be higher,:cry: and I guess my dream of a 40 foot high treehouse will have to wait a while....

Brad and Treeslinger, thanks for the info and simplification! Even ol Edward (special Edward, that is) can port a saw now! ¡Muchas gracías!

Edward
 
teacherman

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So you ready to tear into that 084 or what?:greenchainsaw:

At least the size would make it easier to get in there and grind on it.
Do you still have the link to the thread about that saw? I am trying to remember, doesn't it have the rev limited coil? If so, it would have to be a torque-heavy port job, which wood make it more like an 090......
 

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