I think the cylinder is bypassing for a couple of reasons. With the rod extended more than about halfway, you can grab the clevis and wiggle it side to side or up and down a fair amount. Also, from the day I got it running, there is a steady stream of fluid that leaks out around the end seal on the return stroke. I'm talking about a serious leak. I have it run down a little peice of 1" angle and collect in a measuring cup and I think it hits the 3-cup line in 20 minutes. I put this thing together for about 65 dollars including the fluid, just having fun. Yesterday, it couldnt split this easy peice of oak, and instead of straining, the engine rpm was probably dropping by 500 or so. I estimated where the seals were, based on how far the rod had extended, and the cylinder was noticably hotter in that small section than any other part of the system. My valve and pump were normal temperature. I verified this with an infrared thermometer. I should also say that this situation didnt happen suddenly, but it wasnt really gradual either. No, I dont have a gauge in the system anywhere and I dont have any hydraulic experience. That little test with a hydraulic jack is a great idea that I plan to try out tommorow. If the seal is as weak as I think it is, I may be able to push the rod in without a jack. Thanks for all the info/advice, and I will gladly read any other responses!