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Just finished up a reseal on this Diana 100 match rifle, and in the process, managed to find some off-the-shelf substitutes for three of the four main seals. First point of note - this is not a gun for the neophyte to tackle, so I will not go into a great deal of detail in regard to the teardown and re-assembly. Those with the knowledge and experience to tackle one of these guns is already aware of some of the intricasies involved.
On this particular gun, the piston seal was in remarkably good condition, and did not require replacement. Had it required replacement, an appropriate seal would have to be fabricated, which I would normally machine from 90 DU urethane. Note how the sealing lip extends past the face of the seal. The end of the compression chamber is suitably grooved to allow the face of the piston seal to seat solidly against the end of the chamber on lock-up.
A previous, unsuccessful attempt to re-seal this gun before it was sent to me, left three of the five socket head capscrews with their 2mm hex sockets stripped completely round. I used a tiny carbide dental burr to cut slots into the heads of the tiny flat head capscrews, allowing the use of a straight slot screwdriver to remove the damaged screws. All five screws were replaced with brand new fasteners on re-assembly.
The OEM Diana valve seal looked very familiar to me, and a few quick measurements confirmed that the valve seal from an FWB 60x series gun was similar enough to be a drop-in replacement. The FWB part number for this seal is 1750.214.1.
When re-assembling the powerplant, there is one small item that deserves mention - the small coil spring that acts on the ratchet pawl of the cocking arm. It is supposed to sit in a pocket in the arm, and over a stub protruding from the pawl, but as one tries to maintain all the needed parts in alignment, while tapping in the pin that holds everything in place, this spring tends to jump off the stub on the pawl. If care is not taken, the mis-located spring will be badly bent when the lever is set to the closed position. I had to locate a replacemnt for this spring, as whoever worked on the gun previously, did not take the due care to ensure that the spring was properly seated, resulting in it becoming malformed.
The transfer port seal, which is located in the bottom of the bolt, is another seal that looked familiar, and once again, the dimensions are similar enough to allow the use of the transfer port seal from the FWB 60x series guns. The FWB part number for this seal is 1750.359.1. The arrow points to the seal, which is blue in colour.
There wasn't much left of the original breech seal to give me any idea what it was supposed to look like. It was obviously tapered on the ID, but surely must have been very thin walled. After trying a couple options, which I was not satisfied with, I decided to try using an o-ring, and after checking a few dimensions, installed a 6mm x 2.5 mm o-ring, which fit perfectly, and worked great. Inexpensive, and off-the-shelf replacements would be readily available if needed.
One detail that struck me as rather odd with the Diana 100, is the lack of any locating feature to maintain the barrel alignment in correct relationship to the gun. Typically, most guns have a locating key, a pin, or a flat to ensure that the barrel cannot be installed with the dovetail for the front sight canted. The Diana 100 has a simple saddle to lock the barrel down at the breech end, and the barrel band at the forward position. The barrel is free to rotate 360* until these two clamps are snugged up. The fore and aft position of the barrel is also not solidly positioned, and on this partticular gun, an o-ring was used to fill in the gap between the front of the barrel clamp, and the rear of the shroud, as noted by the arrow. If the barrel is moved back far enough to eliminate this gap, the bolt cannot be closed.
Presumably, the fore and aft adjustment provided for the bolt lock-up was intended to allow some latitude in the barrel placement, but as can be seen in the pic below, the bolt adjustment is all the way back (green arrows), and the barrel had to be set forward as noted in the paragraph above. Note as well when looking at the size of the gap noted by the red arrows, the adjustment slot is far longer than the amount of movement available.
The Diana 100 is a rather unusual departure from the designs used by the other major match rifle manufacturers, and in some respects, at least in my opinon, could best be described as "design by committee". Just seems that the gun is far more complicated than it needs to be - but - for the collector, that would tend to make it both interesting and desireable.
The procedure to cock and load seems a bit tedious at first, but as with any gun, after one develops a technique, it becomes a non issue. As for accuracy, that certainly cannot be faulted in any way. After the initial sight in, I shot a few targets from a seated position, elbows rested on knees, with the front of the rifle on a tripod rest, and every target shot was one ragged hole, of less than 0.200" dia. Definitely a keeper.
