The ol' 4-108 smokes blue a little on startup and usually has to warm up a while before the cloud becomes a wisp. The compression is good, and she runs well. So I decided to see if I could change out the intake valve stem o-ring seals, but couldn't find a spring compressor that would fit into the space above the engine. I thought this rig up, and found it to work pretty well. The height of the plate needs to be enough to clear the valve springs when the are fully relaxed. The plate is 1/4" steel plate. I made the tubing that meets the upper spring retainer from 1" SS bimini tube, and cut a window through the side wall big enough to remove and install the keepers. Coupling nuts (5/16 - 24) and short studs attach to the valve rocker shaft mounting studs and elevate the plate and hold everything in position so that the spring doesn't cock or slide sideways.