Crosman Town & Country 107

[jirushi]

Some improvement:

545 ft/s with 8 pumps, 584 ft/s with 12 pumps (6,4 ft/lbs).
I'm not sure what 107's are capable of? And if they're meant to be used with more than 8 pumps.
I think .177 is going to be less efficient in a pump gun anyway?

Here are the adjustments I've made, following the advice I received from DT Fletcher and ped:

1. align blind hole in exhaust valve body perfectly with hole in tube

2. weaker check valve spring

3. pump rod is now "longer", the pump cup leaves a tiny gap for air to be sucked in through the breathing hole.

Not sure which adjustment made the biggest difference: it would have been best to try one at a time, but I feel that disassembling and reassembling the 107 causes a bit of wear, which I want to keep to a minimum of course.

By the way when there's no pressure in the gun, the forearm drops down. So I guess my pump arm adjustment isn't right yet.
Any ideas how to adjust in order to get it right?
Looking at my 108, the pump cup clears the breathing hole more than my current 107 setup. Hmmm.

[jirushi]

Ps. Whilst looking for info on 107 velocities, I cam across this Baker Airguns ad.
735 ft/s.
Nice. I shall continue tinkering

[45flint]

Some improvement:

545 ft/s with 8 pumps, 584 ft/s with 12 pumps (6,4 ft/lbs).
I'm not sure what 107's are capable of? And if they're meant to be used with more than 8 pumps.
I think .177 is going to be less efficient in a pump gun anyway?

Here are the adjustments I've made, following the advice I received from DT Fletcher and ped:

1. align blind hole in exhaust valve body perfectly with hole in tube

2. weaker check valve spring

3. pump rod is now "longer", the pump cup leaves a tiny gap for air to be sucked in through the breathing hole.

Not sure which adjustment made the biggest difference: it would have been best to try one at a time, but I feel that disassembling and reassembling the 107 causes a bit of wear, which I want to keep to a minimum of course.

By the way when there's no pressure in the gun, the forearm drops down. So I guess my pump arm adjustment isn't right yet.
Any ideas how to adjust in order to get it right?
Looking at my 108, the pump cup clears the breathing hole more than my current 107 setup. Hmmm.

Your pump arm should cam shut and stay closed. Mine came shooting very well and cams just a little, not with as much force as my Benjamin Sheridan C9A. Below I am attaching a UTube of my 108 at the 7:00 minute mark you’ll see me close the pump arm with a little click. When my pump arm is extended my air hole is completely clear of the pump cup. Makes me think that your replacement pump cup assembly may be a slightly different length than the original? To get max power I am sure you need to cam that cup against the intake to squeeze the most air in? But mine is a very gentle cam, slightest of all my pumpers.

https://youtu.be/lTL6xwyBLSw

[jirushi]

Your pump arm should cam shut and stay closed. Mine came shooting very well and cams just a little, not with as much force as my Benjamin Sheridan C9A. Below I am attaching a UTube of my 108 at the 7:00 minute mark you’ll see me close the pump arm with a little click. When my pump arm is extended my air hole is completely clear of the pump cup. Makes me think that your replacement pump cup assembly may be a slightly different length than the original? To get max power I am sure you need to cam that cup against the intake to squeeze the most air in? But mine is a very gentle cam, slightest of all my pumpers.

https://youtu.be/lTL6xwyBLSw

What a great youtube video. I've seen it before, but it's just really relaxing to watch, and you have one stunner of a 108.
In order to find the correct pump rod length setting (it is adjustable in my 107), I will disassemble the pump rod from my 108 and use that as a guide.
I think that will be the quickest way.
I could even test the 108 pump assy in my 107.
It's all good fun!

[--ped--]

when the piston is the correct length you'll find it contacts the valve with 1/2"-3/4" clearance between pump arm and tube and the lever should just nicely close

[DT Fletcher]

Note on setting the over-toggle ("over-toggle" is the official Crosman engineering term for this) of the pump arm. First; it isn't essential but I always check this with the internals out of the gun so that there is no back pressure. You want the pump head to hit the back of the compression chamber then add about 1/8th more rotation. Normally, I do this by feel; it can be clearly felt when the over toggle occurs and you want to set it just a tiny bit past that point. No other adjustment is needed. Like I said, don't worry about the air hole unless there is an obvious problem in operation. If that air hole ain't working right, there will be no missing it in operation.


Checking the check valve: One test of the check valve operation is to pump the gun up to full pressure and then pull back the pump arm and just let it rest there on the bubble of air and observe where it is. If the check valve is slowly leaking, the pump arm will move up.

Trying out the pump arm from the well performing 108 in the 107 might be helpful to determine if the rebuilt pump head is working at high pressure. When I had a low performing gun and everything else was okay, I always suspect that the pump head was leaking at high pressure. Thinking about your rebuild, if the brass ring is not pushed back completely and solid, air will leak past that point.

[45flint]

Woke up in the middle of the night thinking about the pumping arm issue. It makes no sense to me if your pump rod is adjustable that you could not adjust to cam correctly and clear your vent hole? The length of your cup assembly should not matter. The only thing that I can think of that would affect this is your not getting the full upsweep of your arm? Below are pics of my 108 fully up, hole clear and position of arm struts.

[jirushi]

Woke up in the middle of the night thinking about the pumping arm issue. It makes no sense to me if your pump rod is adjustable that you could not adjust to cam correctly and clear your vent hole? The length of your cup assembly should not matter. The only thing that I can think of that would affect this is your not getting the full upsweep of your arm? Below are pics of my 108 fully up, hole clear and position of arm struts.

Haha nice that the pump arm issue made you wake up in the middle of the night
You're right, as my pump arm length is adjustable, I will definately be able to find the right length.
Taking the pump rod out of my 108 to use as an example, will make things easier.
Then who knows I'll get to higher power!

[jirushi]

So this morning I took the pump arms out of my 107 and 108.
The 108 arm was about half a cm shorter.
I adjusted the 107 arm to be exactly the same length.
But the 107 forearm still drops down when there's no air in the valve
And the forearm opens up again when I pump the cocked rifle and then open the arm up a little. So there's still a bubble of air in front of the pump cup, which should have gone into the valve.
Perhaps the 107 has a different position of the valve wall in de tube?
As in, further towards the rear of the rifle, so that I actually need to make the pump arm quite a bit longer than the 108 one?
From the outside the actions look identical.
Hmmm.
Will have to do more testing - hopefully tomorrow