av8tor1977

My Feedback: (6)

Frank Bowman, at the e-mail address and/or phone number listed above, sells the special ring with a notch in it for a pinned ring setup in the Homelite 25cc that allows us to grind out that exhaust port bridge for more flow and power. He can also modify the piston and install the necessary pin for you, which is what I highly recommend as it is a rather tricky operation to install the pin. It would be easy to botch the job and ruin the piston, or worse, have the pin come out later and destroy the piston and cylinder too.

However, I have been asked to include the procedure to install a pin in the piston. So here goes:

The pin should be about the diameter of the ring groove. I use a little piece of gas welding rod. You use a drill press to drill a perfectly straight hole about .003" smaller than the size of the pin in the ring groove. You want to locate it where there are no ports in the cylinder, like in between the transfer and the exhaust port. This is critical. Then I use a bit of JB Weld on the pin, and with the piston held in a padded "V" block, very carefully drive the pin into the hole with a hammer and a small pin punch. (It's a three handed deal.) Start it straight and don't miss, or you'll ruin the ring land. Usually you size the pin to be the full depth of the ring land plus the distance of the hole you drilled, so as to be able to handle the pin and drive it in properly. But the pin has to end up being only 1/2 the depth of the ring groove. So you have to very, very carefully grind or file down the pin until it is only sticking up halfway into the ring groove. Once again, this is critical as if you don't get it right, you will either break Frank's special ring when you assemble the engine, or have a tight spot there because the pin is holding the ring up. Not good! The other thing is most people don't realize that the piston ring must seal on the bottom of the ring groove in the piston as well as against the cylinder wall. If you damage the ring land, or groove, the ring won't seal well and the engine will be down on power.

Note that the Homelite 30cc engine, which is identical to the 25cc except for the bore size, has a pinned piston and an exhaust port without a bridge from the factory. It weighs exactly the same as the 25cc, and is a better candidate for your airplane engine. As of the date of this posting, I have been seeing Homelite 30cc engines in the Ryobi brand of string trimmer, and in some of the Homelite brand handheld leaf blowers.

AV8TOR