I have a new set of venolia 392 pistons( got in a trade) - i want to use them with my micky thompson rods. The problem is that i dont have the buttons -and want to convert to a standard wrist pin circle clip/ spiral lock . Has anyone ever cut this groove in the wrist pin area - I have a mill, I don't figure it to be that hard - anyone ever done this or know how ???? thanks mitch
I would think mounting the piston on a Mandrel in the pin bore, in a lathe then making a small tool to hook into the bore and cut the groove would work well, there would be a way to achieve the same thing on a mill, but cant visualise it as easy
some buttons where a teflon looking plastic other buttons made out of aluminuim make your own .....use assembly lube to hold them in place
Make you own buttons...much better than clips that CAN come unseated and ruin your cyl walls....With a mill you can make some from teflon...
It can be done in mill using a boring head that cuts outward, the old timers called them "curly heads" and they weren't that accurate. I would do them on a lathe using an expanding collet, but can only pick up so much of the hole that you are boring. With a little shop math and a standard groove tool in a holder, it can be done. Bob
You can cut them on a mill by mounting them on a rotary table and using a woodruff cutter. Make a fixture with a flat plate to bolt to the rotary table that has a spud sticking up the size of the pin hole (a wrist pin works) that is just short of the spiralock location that you want to cut. Hold the piston down with a clamp on the inside of the pin boss or piston skirt. This is basically the same as on the lathe with the rotary table as the lathe chuck and the woodruff cutter as the lathe tool. CNC mills do it quicker and easier as do CNC lathes. Buttons are better and can be easily made with the right equipment. My son Richard at Hartman Machine Works/Horton Race Cars can make a custom set for you very reasonably. Virgil
Bingo, you are right! Just find center, dial off in the Y axis to your magic number. Snap ring grooves always have a + dimension on their sizing. Bob
Yes it is easy on a lathe, I made an expanding mandrel not hard to do if I can explain with out a picture. I do this for a lot of other things that one needs to hold onto with a hole in it. chuck up a piece of brass, steel or alum and turn it to a slip fit in the pin hole cut it long enough to catch the second side or out side pin hole but leave short enough to cut your snap ring. Now drill and tap the end for a pipe plug I use a hex plug then take and band saw a slot through your tapped hole and go about 1 inch past the tapped hole or so that it will expand when the plug is tighten in place. there you have it clear as mud A! There maybe some one out there with a better Idea I don't know I have been machining for 40 years and seems theres guys with some very clever ideas out there. good luck
If the pistons have offset wrist pins, then buttons can not be used simply because they will have a tendency to turn or rotate when contacting the cylinder wall unevenly.
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