As I mentioned in the first sentence of the posting about pinning the piston, the pin should be whatever you can find that is about the same diameter as the width of the ring groove. It is a bit tough to drill a hole in a ring groove that is larger than the diameter of the groove, and often times when you try to do so, you will break a bit and/or damage the ring groove. That's why I suggest measuring the width of the groove, and then planning to use a pin that is close to the same diameter. Do not quote me on this, but it seems as though the last time I did one, which was some time ago, I used a gas welding rod with a diameter of .063" to make the pin.

Then, since you want a press fit in the aluminum for the pin, I suggest precision measuring the pin with a micrometer, and then using a drill bit that is .003" less than the diameter of the pin for your hole in the piston. You will really need a drill press and a "V" block for the piston for doing this procedure, as the hole has to be perfect. If done by hand, it will surely not be perfectly straight nor round, and you will not be able to trust the press fit of the pin. That could be disastrous for the engine.

The depth will vary with the different pistons encountered with the various Homelite 25cc engines. In some cases, you will break right through the ring land while drilling, and of course, that is as deep as you can go. In other cases, the drill will go partly into the piston crown, and partly into the interior of the piston. Once again, that will determine your depth, as once the hole breaks through to the interior of the piston, don't bother drilling any farther. And lastly, the drill might go entirely into the piston crown, and never break through to the interior area of the piston. In that case, I would drill the hole, let's say, approximately the same depth as the depth of the ring land.

Sorry but I do not have any pics of me doing the procedure. I had figured on referring people to Frank Bowman for doing it, as it is a fairly critical operation. However, I have recently been informed that Frank is so busy making rings for customers worldwide, that he does not have the time anymore to do the pinning operation. So, proceed very carefully, and be patient while doing the procedure. As mentioned, I use a tiny bit of JB Weld on the pin when punching/pressing it in place. Just be sure to clean any excess JB Weld away before it dries. And when you grind that pin down to be only half way protruding into the ring groove, be super careful that you do not damage the ring groove while doing so.

AV8TOR