A simple tube spanner can be made to remove the rear inlet valve body. Recently I decided to make one out of some aluminum tubing of 19 mm OD and 16 mm ID. I had thought that this would be too thin and weak in cross-section for the job, but as I had a length of it from a gun project that never eventuated I decided to make one and see what happened. The two notches in the rear of the Mares inlet valve body are 10.5 mm wide and 3 mm deep, so I cut lugs using a hacksaw onto the end of the aluminium tube that had previously been cut off square to the longitudinal axis of the tube. Aluminium is easy to work, so I removed enough with the hacksaw cutting first downwards and then radially to create the two diametrically opposing lugs which are 3.2 mm high and 10 mm wide, doing the final cutting to size with a metal file. Note that the length of tubing was first held vertically and then horizontally in a bench vice for this work. You can always take more material off with a file, you cannot put it back on, although you can cut deeper into the tube if you need to start again. I made the tube spanner 12 cm long (the tube spanner length is not critical) and drilled a transverse hole through the rear end for a T-bar (using a drill press, but I could have done it in the bench vice after centre punching the tube to stop the drill bit drifting off where I wanted the holes to go). I use an old engine push rod, but you can use a spear shaft if you have a short one that will serve as a T-handle.
It took me 10 minutes to make it and some of that time was spent clearing the work bench, finding a suitable file and two blocks of wood to avoid squeezing the aluminum tube in the bench vice. The key to using the tool is to engage the lugs fully in the slots and give a strong twist with the gun grip held firmly between your knees, there will be an initial resistance and then it will turn, getting easier as it revolves out of the rear of the grip. Sometimes the screw threads will have some sealant on them, but usually they do not as the pressure seal takes place where the well in the rear of the plastic handle molding presses against the large radial step in the metal inlet valve body. I sometimes think this stuff is to discourage DIY efforts, but if so then it is not strong enough. Never use epoxy on your gun or you will ruin it for future dismantling.
This item is so easy to make it could almost be a throw-away tool. I have undone two never dismantled before guns with it and the tool seems undamaged so far despite the 1.5 mm thickness of the lugs. A piece of aluminum tubing with a smaller ID may be better, but as this works I don't think the lugs need to be any stronger unless you were working on a speargun production line.
It took me 10 minutes to make it and some of that time was spent clearing the work bench, finding a suitable file and two blocks of wood to avoid squeezing the aluminum tube in the bench vice. The key to using the tool is to engage the lugs fully in the slots and give a strong twist with the gun grip held firmly between your knees, there will be an initial resistance and then it will turn, getting easier as it revolves out of the rear of the grip. Sometimes the screw threads will have some sealant on them, but usually they do not as the pressure seal takes place where the well in the rear of the plastic handle molding presses against the large radial step in the metal inlet valve body. I sometimes think this stuff is to discourage DIY efforts, but if so then it is not strong enough. Never use epoxy on your gun or you will ruin it for future dismantling.
This item is so easy to make it could almost be a throw-away tool. I have undone two never dismantled before guns with it and the tool seems undamaged so far despite the 1.5 mm thickness of the lugs. A piece of aluminum tubing with a smaller ID may be better, but as this works I don't think the lugs need to be any stronger unless you were working on a speargun production line.