Quote Originally Posted by DT Fletcher View Post
Most anything is rebuildable, given enough time, effort, and the right parts. Back in the day, these pump assemblies were never rebuilt for the simple reason that Crosman didn't sell the individual pump cups. That was the basis of my statement. Today, with replacement pump cups, they can. Which, clearly, is (good) news to me. Same with the old 150/160/180 etc model exhaust valves, until Rick started sourcing the proper seals, these valves were considered non-rebuildable, but, today they are. Fortunately, I tended to keep these valves and had a coffee can of 'em which I proceeded to rebuild with parts from Rick.

Like I said on the other forum, I would never rebuild one of these guns with that small check valve seat: it's unreliable and was replaced in production by Crosman with the large version.

Pump adjustment: Per Crosman factory engineering, the pump is properly adjusted when the pump head presses firm against the air chamber and then just enough more so that the pump rod "over-toggles" which forces the pump head against the air chamber and hold the pump arm firmly in place. No other adjustment is (factory) acceptable.

I never worried too much about the air hole. The pump head is not very effective when run in reverse and unless the pump arm is hard to open up, you probably don't have a air supply problem. In other words, don't use the air hole to determine pump arm adjustment.

Didn't see what oil you're using. Most oils and all oils intended for spring guns, are not acceptable. I presume you're using Crosman oil, or MAC-1 Secret Sauce (I know the secret, if you're looking for a local source) or .....?
Hi DT, thank you kindly for all the interesting info and thoughts.
Especially the pump adjustment info is very interesting - I bet the power issue of my 107 is partly due to wrong adjustment. I think I've over adjusted, meaning that the rod is screwed into the piston pivot block too much. This explains why the forearm drops down easily now.

Then the small check valve base. Will have a look on the JG airguns website if they sell the larger version.

The gun has held air overnight.

I used silicone grease on the seals. And a tiny bit of moly grease on the metal parts of the pump rod that make contact with the tube wall.
Do you think that this would cause issues? I have Pellgun oil, no "secret sauce".

@ Ped, I think the exhaust body is aligned properly; the blind hole on the exhaust body (see drawing) is aligned with the hole in the tube.
Good idea to use an o-ring in lieu of the flat exhaust valve body seal.
The seal seems to be working now though.
What kind of paste do you use for lapping?