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There are two types of pumps for the M. One has a button top with a large cantilever that pushes it and the other has two "ears" that are pushed down by a fork mechanism. Both are activated by the exhaust cam. I just repaired one a few nights ago for an M I am restoring. Now on to your question: The plunger should be about 3" long and , I think, 3/8" in dia. I can get you the exact dims. if you really need them. There is one ball that sits at the bottom of the plunger bore and is held in place by the plunger shaft. This is the incoming check valve from the tank. There is another ball that sits at the bottom of the outlet chamber and this is the output check valve. This is accessible if you remove the brass compression to pipe fitting adaptor on the angled output chamber. Both balls must move freely for the pump to work. In fact, with the plunger removed, the plunger ball should fall out when the pump is inverted. Most of the time they are stuck in their seats after a period of setting. The ones in my 1930 M are steel and easy to get out with a magnet. My 1918 M has brass ones and a small wire was needed to poke them out from the bottom (inlet). Also, the plugger rod must fit the plunger bore without too much side to side play. The next thing that you will find, once the pump works, is that there is gas spewing out the top of the plunger bore. This is fixed by replacing the packing under the packing gland at the top of the plunger bore. Sometimes the packing gland has to be replaced since it must be destroyed to get it out, especially if there is a lot of corrosion around it. The only thing that should be holding it in is the return spring for the plunger. Be careful with the pump housing. I believe it is made out of pot metal and will break with too much force applied. hitnmiss.com has all the parts - including the entire pump if yours is beyond repair. Regards, Wade
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