Diana Giss advice needed

[NeilnrLincoln]

Hi.
I've recently bought a Diana model 60, it shoots very smoothly but the cylinder end cap has no locking screw & the hole for the locking screw is nearly 180 degrees out (at top instead of the bottom).
I've just taken the cylinder end cap off to have a look & the rear piston is practically flush with the end of the cylinder where I believe it should be set back around 0.3mm?
There is the stepped spacer inside the end cap but no shims behind it and the step was facing the inside of the cap and not (as I would imagine it should be) facing into the cylinder.
I'm guessing the step in the spacer should fit into the end of the cylinder but on mine it tightens up against the end of the rear piston before the cap is screwed all the way home.
Any advice where to go from here?
Thanks.
Neil.

[Garvin]

Hi.
I've recently bought a Diana model 60, it shoots very smoothly but the cylinder end cap has no locking screw & the hole for the locking screw is nearly 180 degrees out (at top instead of the bottom).
I've just taken the cylinder end cap off to have a look & the rear piston is practically flush with the end of the cylinder where I believe it should be set back around 0.3mm?
There is the stepped spacer inside the end cap but no shims behind it and the step was facing the inside of the cap and not (as I would imagine it should be) facing into the cylinder.
I'm guessing the step in the spacer should fit into the end of the cylinder but on mine it tightens up against the end of the rear piston before the cap is screwed all the way home.
Any advice where to go from here?
Thanks.
Neil.

Neil it may be that whoever serviced this rifle found that turning the step towards the seal pushed it in too far when the cap was screwed on and it interfered with the gear timing, because the seal was already nearly flush with the end of the cylinder?

I'm guessing that on some rifles moving the piston rack forward by one whole tooth before putting the ratchet wheel in moved the rear seal quite some way back into the cylinder, making several spacer shims necessary? If you didn't have them handy it must have been tempting to get away without them?

I'm not sure the cap locking screw was really necessary, because the threads are so fine and the cap is very well screwed on anyway. I suppose over time the cap could unscrew itself by enough to affect the smooth running of the piston assembly though. A dab of Loctite necessary perhaps?

[NeilnrLincoln]

Thanks Garvin.
It's clearly been apart & fitted with new seals, the rear seal looks an almost new blue type.
If I'm understanding the Giss system correctly the important thing is that it's timed so the front & rear pistons reach the end of the cylinder at the same time, so based on the fact the front piston must be against the front, if the rear piston is just touching the rear spacer when the end cap is screwed on I guess it shouldn't damage itself?
So it should be safe for the Giss system to reassemble as it was with the stepped spacer turned around so the seal just touches it & as you said, a dab of Loctite on the end cap just to prevent it unscrewing?
Thanks.
Neil.

[JLB]

The spacer should be stepped so the rear bumper of the rear piston just about touches it after firing to prevent over travel of the rear piston and trashing of the gears, the shims if any in the end cap are used to adjust it. I believe the screw is drilled at the factory once set up, so may not always line up on reassembly after a service.

John

[Benelli B76]

When the Giss system is completely assembled you can check if everything is spaced correctly by unscrewing one of the side pinions. They should not be under
stress and unscrew easily. I often see these chewed up because they have been forced to centralise in the thread. Also the little gear wheels should look absolutely central while sitting in the two racks and be easy to lift out.

Baz

[NeilnrLincoln]

Oh ok. If I turn the stepped spacer round so it's facing the right way & screw the cap fully home until it stops the caps over the gears on the sides are free to undo & the gears look central, so is this the correct timing/clearance?
Does this not mean that the rear piston is under a small amount of load when the rifle is unlocked, will it not reach the end of its travel fractionally before the front piston?
Sorry if I'm overcomplicating things.
Thanks.
Neil.

[Benelli B76]

Oh ok. If I turn the stepped spacer round so it's facing the right way & screw the cap fully home until it stops the caps over the gears on the sides are free to undo & the gears look central, so is this the correct timing/clearance?
Does this not mean that the rear piston is under a small amount of load when the rifle is unlocked, will it not reach the end of its travel fractionally before the front piston?
Sorry if I'm overcomplicating things.
Thanks.
Neil.

You are a bit. The goal is that the gear teeth are not under load when the pistons stop. If they are assembled incorrectly the gear teeth received a shock loading and one or two can break off. The proof is as I already said above, the caps will be hard to remove because of the side pressure, and the little gear wheels will be slightly off centre when the caps are removed.The large back cap must always be in place when you do this kind of check.

Baz