Diana Giss advice needed

[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

[NeilnrLincoln]

Excellent, thanks for your help. In that case I'll turn the stepped spacer the correct way round so when the rear cap is tightened up the load is taken off the gears & put a blob of Loctite on the end cap to prevent it unscrewing.

[Garvin]

Excellent, thanks for your help. In that case I'll turn the stepped spacer the correct way round so when the rear cap is tightened up the load is taken off the gears & put a blob of Loctite on the end cap to prevent it unscrewing.

I'm sure you're planning to do this anyway, Neil, but as Baz says, make sure you unscrew one of the little gear caps and check the toothed wheel inside is free when the end cap is screwed on (before you Loctite it, obviously!).

[NeilnrLincoln]

Will do Garvin, thankyou all for your excellent advice. I'm reassured now that it's (hopefully) not going to destroy itself .

[dvd]

Will do Garvin, thankyou all for your excellent advice. I'm reassured now that it's (hopefully) not going to destroy itself .

Hi,
it looks like you have a firm grasp of what is happening in the action and you are nearly there.
Three other things I would like to include;

1) Before you do the very important gear cap cover test to see that the gears are not loaded, make sure that the caps turn freely on the threads without any binding, before you insert the gear wheels. Other wise you can get an incorrect feel and think it needs further adjustment at the rear shim.

2) There are about 5 or 6 stepped washers available in 0.2 mm incremental sizes going all the way up to 1.2mm if I remember correctly. The reason is that in the eventual replacement of the buffer and piston-seal these may be slightly thicker or thinner than what was in the gun when it left the factory. So it could be that the new seal and buffer might require a slightly thicker or thinner stepped washer to achieve the correct timing, or you could be lucky and be able to use the original stepped washer because its thickness coincides exactly with the dimensions of the replaced washer and buffer.

3)Last thing is to make absolutely sure that the cylinder's bottom is clean of any left-over pieces of old seal. Otherwise you get a false reading when it comes to getting the right thickness of stepped washer.

Regarding the rear lock screw on the threaded end-cap, the threads on the cylinder are 0.5mm pitch. So if yours is approximately 180 degrees out, that would be half a turn which equates to half of 0.5=0.25mm. So you can insert a 0.25mm shim between the cap's inner face and the stepped washer to align the lock screw's hole.
The lock screw is essential because if the end cap unscrew even by a small amount,, then the timing of the two pistons will be lost.

Good luck with your rebuild........Fantastic guns these Giss type Dianas

[thisisdonald]

All good info... I've got a 75 here that I've bought a service kit for. I bought one spacer just in case. I figured I could make up others from shim material easier than ordering from Germany.
Lots of good info on this video as well:
https://youtu.be/8rEIZas_v-M

[Benelli B76]

One of the 6 M I have done, gear just drops in loose and central. You are able to screw in the pinion caps quite a way with fingers, no mole grips !

Baz

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