634 piston works in a Hirth 300!!!!
As a kid, I was completely HOOKED on old sleds. I had the intertec manual memorized by the time I was 12. Anyway, I looked through the bore & strokes of all those engines and found that the 300 and 600 had the same pistons. They also show a 317 that shared pistons with the 634 twin. These engines have the same stroke as the 300& 600. I hoped that you could bore out the 300 cylinder and put in a 317 piston. Then My buddy Mike told me he did that 5 years ago to the 300 in his 67 Panther and has been running it ever since. So I did it. Even the ring pins line up in the cylinder. Another advantage is the 634 piston only uses 2 rings, so you get a little more revs, and you can run a leaner oil/gas ratio. There is plenty of meat in the cast iron cylinder on the 300 and the ports wont get distorted from the large bore. I haven't run my 300 yet, but Mike's Cat has been run for 5 years, so I take that as confermation that it works.
Re: 634 piston works in a Hirth 300!!!!
Well its official! My 300 runs perfect. Started for the first time today and let it idle for an hour. THE 634 PISTON GAVE NO TROUBLE.