Eisenwerke Gaggenau MF in trouble

The patent drawing already shows this, always without a piston seal.

Probably the earliest examples had no leather washer and relied on a metal-metal contact for the seal. However, in my experience most examples seen had pistons fitted with a leather washer, and almost always the leather will have disintegrated with only traces left, or none at all. Here are four different examples of piston heads from MF pistols, three of which have studs.  Traces of the leather washer can be seen on two of the pistons.  The central rod should certainly screw out in most cases. 

The Dare Devil Dinkum, bottom right, is a late example and not typical in that the leather washer is retained by a central screw rather than peened over studs.      

Thank you folks - that is extremely helpful. My pistol seems to be similar to John's top right picture and is serial number 15757, with a separate cocking key, curly 'patent' on the LHS and crossed pistols on the RHS. I'm still unsure about the piston rod - from the pics it seems that the piston head would unscrew off the end of the rod, but would be secured by peening over the threaded end. In that case mine would appear to have been further screwed down, leaving  enough thread exposed to grip and damage. If so then the piston rod would hit the cylinder end and the piston would stop prematurely. I guess I need to do some measurements. I'm reluctant to force the piston to move either way unless I know it is meant to.

I've attached photos showing the piston and face, the broken 'bobble' end and my proposed solution - file flat, drill & tap for a spherical-headed screw. Comments or suggestions welcome!

I think the big problem with the MF piston was the method of fixing the leather washer to the piston head. The two peened over studs would have been OK until you needed to replace the washer.  By that time the studs would have been squashed and too short to be used again with a new washer. Being recessed makes things worse.  It seems that the owner of your pistol tried to get round the problem  by screwing the cocking rod out and peening it over the replacement leather washer, and the washer has now long since disappeared.  I think your suggestion is OK if you want to avoid using a leather washer, but you might find air loss too much. You could use the same technique to accommodate a leather washer, which should improve power a lot. You could glue two leather discs together, one sized to fit in the piston head recess and the other a good fit in the cylinder, then countersink sink your screw below the leather washer so that it doesn't hit the end of the chamber.

I like the way you have solved the problem of the broken off bobble bit. 👍    

P.S. I have never seen one of these pistols with a serial number before. Could you post a pic?  Thanks.          

Thank you, John. Great suggestion about the stepped leather washer. I think I may grind down the damaged threaded end and see if the piston can be unscrewed, then fix it with Loctite flush with the threaded end. Alternatively, drill and tap the new clean end for a countersunk screw to secure both the washer and the piston. I need to be sure that there is enough rod on the outboard end to reach the butt opening, so I'll do some measurements.

The serial number is under the breech bolt (pic attached). I have another MF with no visible number, which appears to have been a T-handle model but the handle has been replaced by a brass knob of sorts. I didn't want to pull this one apart in case it was different and pointless.

The 'bobble screw' is a spare part for the suspension on radio-controlled model racers and is available in different sizes; it remains to be seen whether it is strong enough in tension.

Thanks for the pic. Intriguing - there is always something new to learn.

Cheers,

John

I've never seen a serial number on an MF air pistol before. Also, the "7" looks very strange.

I agree, it's a bit odd. Suggestions in the hat...

Look what I found....I was examining the piston more closely and found what appears to be the last two digits of the number (57) stamped on the underside (see pic). This would correspond with the common practice of identifying gun parts with a portion of the full serial number.