Excellent! Keep us posted on your progress.I got a cylinder i can practice on thanks to super!!! :yourock::yourock:
There is some good info in this thread, at least there was for me.I will reread this this week and take pictures and get involved. What should i use a carbide burr? or start with a slower stone.
I also think it is prudent to look at the ring/s. If the ring has a sharp edge you may want to take the edge off with a bit of emery cloth or very fine carborundum sandpaper.
I don't bevel my ports. I use a bit of fine sandpaper on the end of my finger and pull/push it across the newly ported area. You can tell with your naked finger if the edge is still sharp.
If I am trying to get the transfers to direct the flow, then I don't want a bevel on the nozzle end of the transfer, I want the flow to be tight so there will be less mixing and shortcircuiting. I just use the sandpaper to take the edge off. On the exhaust a bevel is ok as it can help direct the flow into the port.
Originally Posted by Terry Syd
I also think it is prudent to look at the ring/s. If the ring has a sharp edge you may want to take the edge off with a bit of emery cloth or very fine carborundum sandpaper.
Best to leave the beveling for the cylinder and let the rings do their job.
Thanks Ed and Timberwolf, I didn't touch the ring at all, only put a slight bevel on the roof, and just a touch on the floor, but I only used a grinding stone, moving it by hand across the edge. So it is very slight in that regard.+100% sanding the edge of the rings is a bad idea, to work rings must have pressure on the back side to make a seal, if there is a bevel on the front side it will allow cylinder pressure to move down the front side of the ring and will work against the pressure on the backside to unseat the ring and increase blow-by causing loss of charge purity and power, also at higher RPM unseating rings can cause problems with ring flutter.
Bevel is importaint, esp the wider the ports get. However the plating is only a few thou thick so it is surprising how little bevel is really needed. A shallow angle bevel is a lot beter at coaxing the rings into place than rounding the edge off.
Also Having absolute square edges on the discharge edge of a outlet actually causes more resistance to flow and turbulence than having a slight radius on the edges of the discharge orifice.
+100% sanding the edge of the rings is a bad idea, to work rings must have pressure on the back side to make a seal, if there is a bevel on the front side it will allow cylinder pressure to move down the front side of the ring and will work against the pressure on the backside to unseat the ring and increase blow-by causing loss of charge purity and power, also at higher RPM unseating rings can cause problems with ring flutter.
Bevel is importaint, esp the wider the ports get. However the plating is only a few thou thick so it is surprising how little bevel is really needed. A shallow angle bevel is a lot beter at coaxing the rings into place than rounding the edge off.
Also Having absolute square edges on the discharge edge of a outlet actually causes more resistance to flow and turbulence than having a slight radius on the edges of the discharge orifice.
You cannot get that profile with a porting tool. You can get it, or close to it, by using a bit of fine sandpaper on your finger tip and touching up the edge of the port. The center of the port will have more profile than the area closer to the edges of the port. You can stick you naked finger in there and feel the difference as you smooth it out.
Here is the lower side of an exhaust port I was working on. It's not perfect, but I think a decent job with a round stone. The angle of the cut is fairly constant across the port, but tapers to near nothing at the port edges.
timberwolf,Here is the lower side of an exhaust port I was working on. It's not perfect, but I think a decent job with a round stone.
This is something I've been wondering about. How does one go about setting the timing on these saws. I have seen reference to marking the flywheel somehow and using a timing light, but not sure what to do...or even if that can be set.Another thing about the beveling on those ports - timing.
So, how does one calculate the port timing, that must be based on the openings and/or angles of the ports, but somehow the transfers seem to have an effect on all of it.The reference was to port timing...when the ports are open and closed, not ignition timing, which should be fixed unless you take the key out of the flywheel or use an offset key.
Port timing is altered whenever you use a different-sized gasket, or cut a port to change height.
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The old motorcycle books recommend a 10 degree angle, 0.5mm deep and 2 mm in height. Probably a little excessive for chainsaws? The only rounding, however is right where the bevel meets the port.
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so TW, is the the way all ports should be beveled or is this specific to racing saws with a different taper of the radius for work-ported saws? is the intake beveled differently?
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