I needed to verify the installed height and seat pressure of some new valve springs for the Sunbeam. I don’t have a fancy valve spring tester (a Rimac would be nice), so I improvised one with my drill press. I’m not the first person to do this, but I was surprised at how easy it was to set up and how well it worked.
I used my existing Craftsman 8-in. Drill Press, but pretty much any drill press should work. I placed a digital postage scale (mine is an inexpensive Ultraship U-2) on the movable platform (it barely fits). A scrap piece of aluminum helps distribute the spring force across the scale and also prevents the spring from damaging the plastic bed of the scale.
To compress the spring, I made a simple adapter using a 1/4-20 bolt and a large fender washer that was left over from a FLAPS seatbelt kit. I put the exposed threads of the bolt in the chuck of the drill press. Easy.
To use this setup, I place the spring on the scale and push the tare button to zero the display. Then I raise the bed until the spring is just about to touch the fender washer. Finally, I pull down on the handle of the drill press to compress the spring.
A small ruler can be used to mark the desired compressed height of the spring. Continue lowering the chuck until the bottom edge of the fender washer lines up with the desired mark on the ruler, and then read the spring force on the scale. If you have the ruler resting on the scale, as shown here, don’t forget to include the ruler when you tare the scale (or just ignore the small error it introduces).
I wouldn’t expect better than +/- 1 lb. accuracy with this setup, but it works very well for my purposes and helped me confirm that the spring forces and installed heights are correct for these springs.
Side note, the installed spring heights in the Alpine Series V workshop manual are incorrect! Use the heights in the Hunter range manual (WSM 149) instead.
