German-market (F-Type) Crosman 1377

[danco1987]

There will be a bleed hole on the end of the valve near where the valve stem exits if there is one at all. I know the Canadian versions have this, I had a 2289 backpacker from Canada which had one. It prevents the valve reaching high pressures. If youre getting a flat top piston and valve from gmac then I wouldn't worry about this.

Gmac does have the the hollow probes in 177 now. They definitely increase fps, exactly how I don't know, probably channel the air more efficiently behind the pellet. He has videos showing this. They also make loading easier and smoother I find.

[RJVB]

Yes, I also understood the Canadian versions have some kind of bleed valve (from the review on replicaairguns.com). And I was indeed hoping that by installing the flat top kit, I'd simply be getting rid of anything of the kind

I'm a bit peeved I didn't notice the hollow probe for .177 ... I can easily imagine how it makes loading easier (maybe even compensating for the increased difficulty with the gmac breeches?). From the image it would seem that it sits over the transfer port and thus maybe helps to concentrate a bigger amount of air directly into the pellet skirt? I haven't seen a lefthand version though, have you?

[danco1987]

If you get the left handed breech, I think the bolt is threaded through so you can screw the handle into the other side - is that what you mean?

[RJVB]

I think I'll have to ask confirmation. The bolt that came with the left-handed breech is not an ambidextrous design; the handle screws in on one side only.

[RJVB]

Coming back to this subject: I received the GMac FT valve & piston kit, and am looking for some advice on how best to install it - i.t. with minimal disassembly (surprisingly I haven't yet found any 'tutorial' online). Looks like the air chamber/valve is held in place with a single bolt or screw; is that the front screw that holds the trigger assembly to the main tube? Even if it is, I'm guessing I'll have to drop the assembly in order to unload the pressure exerted by the hammer spring? Does that mean the breech has to be taken off too (to avoid damage to the transfer port seals maybe?)
If one has to disassemble to that point, I guess it'd be best to do the extraction and insertion of the new chamber via the rear end of the tube?

[danco1987]

The whole gun has to come apart in order to get the valve out. Its quite simple to do really.
1. First remove rear breech screw and the small breech screw under the bolt in order to remove the whole breech and barrel from the barrel band. Also remove the transfer port and seal.
2. Remove trigger frame screws - front and back. The front one screws into the valve. Watch out for the tiny safety spring screw and ball bearing. Keep the pistol upright when you do this.
3. Next extend the pump arm and tap the pivot pin out using a punch and hammer. The barrel band can then be removed then with the piston.
4. Tap the piston pin out and replace with the flat top. You will need to adjust the piston when reassembling.
5. From the back of the pump tube - use a piece of dowel, I use a wooden chop stick to gently tap the valve out. The valve has to come out the front of the pump tube, so tap from the back.
With regards to adjusting the piston - you should feel the piston end meet the top of the valve when the pump arm is about 1/2inch from closed.
A heavier hammer spring will allow the valve to dump more air. Inside the valve, the valve return spring determines the amount of air taken in during each pump. The lighter the spring, the more air is taken. Also a lighter return spring means the hammer spring can dump more pumps.
I'd recommend a slighter lighter spring for your valve and a sdcustomdesign hammer spring and guide for smoother firing cycle.

[RJVB]

Thanks Danny! I'd already found "miketheknife's" disassembly video on youtube, but more instructions is better than less
Does the valve have to go back in the way it came out? (I suppose it could well become obvious once working on the gun ... but it'll be a few more days before I can get my hands on it again.)

René