trials flywheel weight

[cuzncletus]

I tried to find a weighted flywheel for my Wombat trials motor but was unable to locate one. A friend showed me his weight and I copied his on my 1936 vintage small lathe. I drilled out the four rivets on the points cam at 90, 180, 270, and 360d's for attachment with hardened screws. But when I tried to thread these holes, I found the metal in the cam plate and flywheel exceedingly hard. I ruined six 1/4" taps and had to up the recommended drill size for threading up from what all guides recommended me to use. I'm not a machinist and a backyard mechanic at best, but I have tapped my share of bolt holes. My cobalt bits were screaming when I enlarged the holes in the flywheel. I've never encountered anything like this. Has anyone else had similar experiences?

[TheBevman]

Cuzncletus, while I haven't done the mod you're mentioning I have had the unfortunate luck of trying to drill hardened plate. I was making motor mounts for my ol' 1955 Dodge Truck from some scrap 1/4" plate that I got from a local metal recycler. I didn't have any problems cutting (w/ oxy/ace) or arc welding it... but when I tried to drill a few bolt holes in it . In short after killing a set of Harbor Freight bits I decided to go big or go home with a 7/16" bit and in short order the bit caught and my Milwaukee drill almost separated my wrist, took me about 3 weeks to recover from that one. I know it won't work in your application... but I used my torch and burned the holes. Lesson learned.

[Bullfrog]

The magneto side flywheel weight on my Bullfrog engine has a giant "bolt" which uses the flywheel puller threads to hold the added flywheel weight on. There are also roll pins used to register in the "windows" of the magneto flywheel to "lock" the two items in register.

steel flywheel wt with "puller" thread "bolt"

Another (more popular) method of adding magneto side flywheel weight is to machine a weight which is a press fit over the OD of the flywheel.

press fit brass flywheel wt

Ed

[cuzncletus]

Bevman,,I get the wrenched wrist story. I'm typing this in a brace right now from pressing down so hard to get the taps started.

Bullfrog, the first picture is interesting in that it looks simple, short of finding the proper bolt for the flywheel puller thread. The weight is about twice that of the one I built. The brass one is out of my league both in diameter and precision. My three jawed doesn't run true enough for that much of press fit in my nearly century old small lathe.

[Bullfrog]

The puller thread bolt in the photo was made from scratch. However, if you weld (or have a welder friend), it seems like a flywheel puller body could be modified to do the job. Note the "jam bolt" near the edge of the "bolt" head - to lock the bolt in place.
Ed

[junker2k]

I used a steel (125cc) flywheel to start with. Then I took some round stock and cut it down to the same dia as the flywheel, then I welded it on. From there I cut it down so the case would go on with some room to spare. then I would trying it out and kept cutting the center out till I got the response that worked best for me. Just because you can add a lot weight, it may not work the best for you. By adding weight to the flywheel, it would be a good idea to weld the crank pin.
Jack K