If you're starting to experiment more in moped life with faster and higher revving motors then you must know that any modification to your engine components that will help performance or lengthen its life is of course a good thing. Fighting heat build up is one of the most important things to build around. Some might say that the gains might not be worth the effort But in my opinion they all add up and could save you from the embarrassing call for help or worse a seat in the chase truck at a rally.
This page will show you how to build ring land gas ports in your single ring piston that gives the cylinder walls a small amount of cooling quelch of pressurized air/fuel from the cooler case charge that is waiting behind the piston. So on the down stroke instead of all the colder fuel charge coming into the cylinder through the transfers, some of that charge is vented through the ringland ports and smeared directly on the cylinder walls.
I have done this to all of my performance motors and have had temp drops of 18-30 degrees. I have also noticed that after doing this mod I can now run WOT indefinitely when before I had to lift after about 45 seconds to allow the temps to creep back to a safer level.
I have just finished ring land ports in this Polini W port piston. At the same time I also build a "digwell" for the wrist pin that allows you to remove open ended wrist pin clips.
I will also show the "digwell" process. It is the same as the ringland building.
Things you will need are a drill press, a few 3/32 drill bits, and some stainless steel hose clamps. I recommend using a drill press as it is VERY important that the piston is mounted secure and that the cutting bit is not wavering. If you mess this up, and most certainly will with a hand drill, well then that's $75 gone for a new piston.
Here are some of my hose clamps I have used. You can only do about one piston per hose clamp as although very hard the stainless steel guide hole will start to elongate and then the port hole you are creating will be misshapen and you might accidentally graze the lower ring landing wall. I will show later why YOU DO NOT WANT THIS!!!
If your stainless guide hole is misshapen you simply drill a new hole in the hose clamp.
It is a good idea to insert your piston in its cylinder first then mark where you want your ports to be. You can put them any where but I feel it is best to have them so that they paint the walls of the cylinder most of all.
It will not hurt to have them crossing over a transfer window.
It is very important to have a nice cradle to secure your piston but I don't recommend clamping your piston down solid. You will want to be able to gently pull the piston while drilling so that the bit cuts the top ring land toward the crown of the piston.
It is natural for the bit to want to walk Into the center of the ring land groove in spite of the bit traveling through the stainless steel guide hole. That is why the clamp hole becomes elongated after a while and must be renewed.
You must first drill your guide hole in the hose clamp. The clamp pictured here has very elongated holes so I will drill a fresh hole.
When you install the drill bit in the chuck you want to leave about 1/4 inch hanging down. Because it is such a thin bit it will flex a lot and make it want to wander more. Leaving just 1/4 keeps it more ridged and cutting straight.
To first drill the guide hole in the stainless clamp I position the clamp further down on the piston from the ring groove and screw it tight. It will not hurt to use this portion of the piston as a back up for drilling the 3/32 guide hole in the clamp.
Drilling the stainless clamp is very hard and will take a while and will dull the bit for sure.
When the guide hole is done you can move the clamp over the top of the ring groove and clamp it tight. You want to position the clamp so that about 3/4 of the guide hole is filled with piston to be cut. You do this because you have to compensate for the drill bit wanting to wander to the center of the ring groove.
Here is a close up shot of the positioned clamp on the top of the ring land. This was near the end of all the port drilling so you can see how the clamp guide hole has become elongated. For best results don't use the same bit that you used to cut the guide hole through the stainless. Swap in a fresh bit
Now I am drilling the port holes. You want to be patient and travel down slow and to be sure to cut deep enough. A port that is not deep enough is the same as no port at all. You must go deep enough so that the full 3/32 of the bit diameter is cut into the bottom of the ring groove.
Any less and the cool gas/air mix from the case may have trouble getting around the inside of the ring to even get to the port.
This port is a good example and totally acceptable in depth. It is not too close to the bottom ring land but close enough for the cool gas/air to quelch around the back of the ring on the down stroke.
OOOooo this port is as dead solid perfect as you can get. Any further down and it would have nicked the bottom landing. The reason you want to avoid nicking the bottom land is it will cause a reverse "Hot gas" porting during the compression stroke.
Here is a Honda piston that I ported and had nicked the bottom landing. You can see the nick caused blowby.
Another keeper port Woo Hoo.
Another kit saving practice I use is the use of open end circlips on my wrist pins. I have lost two kits to circlip failure in the beginning of starting this hobby. The first was like "oops". The second was like "what!?! Anyway both failures were with the clips with the tail on them. Could be people say "you didn't position it correctly". Since I started using the open ended clips all the guess work has gone out of the installation because they just cant jump out.
Using these style of clips is a little more work in that you have to drill what I call a "digwell in the wrist pin opening of the piston. Thes "well' then allows you to remove the clip so you can remove your piston.
Remember that the tighter you twist up your little engine the more forces come into play and some of the forces will act on that little tail of the clip and could cause it to jump.
For drilling a digwell you use the same tools and principals as ring land ports. You will want to switch to a 1/8 or bigger drill bit. Position the clamp to the side of the wrist pin hole and clamp it tight. Then drill as before till you have gone just past the wrist pins circlip groove.
When all the drilling is done I like to finish up by lightly sanding the ported areas with 800–1000 grit paper under soap and water. Is all this work necessary? Maybe not but I feel better and more confident in my builds and I wont be scared to push my bike as hard as any of the others running next to me.
I am now done with this page. You can contact me with Questions as Cheetahchrome.