I have a tire hammer from the build in 2007 when we had Clay Spencer come up. For those of you who have seen this style of hammer you know they have a tup-in-a-tube style guide with shims to take up the slop in dimension. Most the shims are metal but the shim closest to the tup being made of Ultra High Molecular Weight Polyethylene (UHMWPE) to also function as a bushing. In the ones we built in the workshop we used little pieces of angle iron welded on the top of the tube as a hook to keep the shims from riding the hammer up and escaping. Except on mine this never worked well. On the up stroke of the hammer there was enough side to side play of the tup to just nudge the angle iron hook just a bit each time. After a short while there was enough of a gap that the shims would ride up forcing me to stop working, push the shims back into place, and tap the angle iron hook back into place with a hammer. This would just buy me a little time before having to do it again. I mulled different fixes but it never pissed me off enough that is jumped to the head of the to do list.
At the Madness last year I looked at the tire hammer Clay Spencer brought with. It had a different method to hold the shims in place. A inverted "L" of maybe 1/8" x 1" flat stock. The short leg was the hook while the long end was welded on to the guide tube. I think the idea it the L gives it a little spring to cope with the side to side motion of the tup when cycling. Not being one to reinvent the wheel when someone else has done the work I went home and tried this... and it still didn't work. I don't know if there was some subtlety to the "L" or it's attachment to the guide tube I missed but it too got bent out of the way and soon let my shims become free range. Now it had moved to the top of the list.
I took the L concept to the next level. I made it a spring loaded see-saw. The business end has a thick piece of UHMWPE that stays in contact with the tup. It is held in place by a poly bolt and a slight lip of steel to keep the poly bolt from having to take sheer force.
- close up of shim stopper.JPG (369.95 KiB) Viewed 3901 times
The other end of the see-saw has a piece of spring under it to keep the business end pressed up against the tup. I set this see-saw in the housing made of a piece of thin walled rectangular tube with one narrow side cut off making a deep U channel. With another scrap of sheet metal tacked on the bottom of the channel it helped to keep the spring in place and keep anything from getting caught up in it the see-saw.
- side view shim stopper.JPG (498.3 KiB) Viewed 3901 times
I am sure it is more of a complex fix than is truly needed but it is a fix. I haven't had a shim escape since welding this on. I don't think everyone with a tire hammer had this problem, maybe my hammer has more slop or the shims were just the wrong thickness or something but it is no longer a worry. If you do have a tire hammer and the same problem I would love to see what you came up with to solve it.
Martin