NECESSARY ADJUSTMENTS Germany meets America, as the Weihrauch HW98 gets its new insides
Last month left us with an introduction to the Vortek custom-made powerplant, and an HW98 in many pieces. This time round we get to put it all together, with a few more nips and tucks before getting it out on some targets for a proper workout. Due to the nature of the kit we are fitting, there is one particular job that needs to be done in preparation.
LOSE THE LINER
Because the Vortek kit has its own integral liner, it is necessary to remove the factory-fitted steel piston liner, which with nothing to grip at first can seem daunting. Get yourself a nice block of wood, and tap the piston down on the block. The sudden deceleration should ensure that the momentum for the sleeve continues, which will result in the liner starting to emerge from the piston skirt. When there is sufficient material protruding, grip the edge and gently tease it out. Try not to damage it because it could be useful for another gun. It might be useful to ensure that the new liner enters the piston without hindrance as this one did – a nice sliding fit.
Keen to go the whole hog, I decided I would fit the Vortek piston seal, knowing that it would require a degree of re-sizing. The old seal prises off easily with a thin, wide-bladed screwdriver, before pushing the new seal into position. Offering the seal up to the cylinder confirmed it would be a tight fit, which would risk damage to the seal if forced, and even if it could be installed, would make the gun hard to cock, and rob the gun of power. To overcome the power issue it would then be necessary to apply extra pre-load to the spring, which will lead to problems later down the line. As the seal naturally wears and conforms to the cylinder, there will be a resultant increase in power, with a real risk of traversing the legal limit – several good reasons to size the piston head accurately.
To start the process, the piston latch rod was mounted in the chuck of a pillar drill. The seal needed to be stopped from turning on the piston, so a length of tape was applied around its circumference at its base, thus leaving the sealing edge free to work on. With the piston spinning, a loop of emery cloth was held against the seal, which slowly and uniformly reduced the diameter. We are not taking off much material here, so be sure to stop frequently and try for size. I aimed to be in a position where the piston could be inserted, with some friction between the seal and cylinder, but easily overcome with fairly light hand pressure. Although not absolutely necessary, the piston body was lightly polished in the same manner, I know that it shouldn’t be touching the cylinder, but it gave me a degree of satisfaction nonetheless.
It was always my plan to fit a quick-release cocking link pin because having fitted one to my HW80, I could appreciate the practicalities of doing so. This decision also made sense on a couple of levels, which materialised during the project. The first involved me being able to get hold of a .177 barrel, which was very lightly used, for a good price, and the addition of the pin meant that I could swop calibres at the drop of a hat, adding a lot of flexibility to the gun.
It is always my preference to fit the barrel, cocking link, and shoe ahead of refitting the main spring because it is easier to fit the barrel and attendant shims without having to deal with mainspring pressure. Because of the new
“it needs to be just tight enought to inhibit any lateral movement, without any binding”
sliding liner design, I thought it would be easier to refit the cocking shoe after the spring was reinstalled because it would then have support from the new liner.
Using a quick-fit pin means you can fit the spring, then the barrel and cocking shoe, and finish off with the cocking link, and quick-fit pin. To my mind these were two good reasons to fit a quick-release pin, but first the old riveted pin needs to be removed.
To remove that old rivet, make sure the breech block is well supported over a piece of wood. I have a block of soft wood with a shallow hole drilled in it, which has enough clearance to allow a pin to be driven through. By using a heavy centre punch, the pin started moving after a few smart taps with the hammer, and the job was finished with a parallel punch of the correct diameter.
PIECE BY PIECE
Now comes the time to fix it all back together. Start with the piston, although the new seal is lubrication impregnated, a little bit of molybdenum grease just on the edge helps to smooth its path inwards, as does a smear on the piston skirt. At this point I decided to use one of the supplied washers on the piston, to give a little extra pre-load, and act as a bearing surface for the front guide (top hat).
Insert the spring/guide set unit, compress and refit the back block in the same manner as it was removed, follow this with the reintroduction of the four square keeper blocks. Taking a look through the cocking slot will reveal that the piston liner will have entered the piston, and will be in far enough to provide a supported track for the cocking shoe.
ROLL IN THE BARREL
Next, the barrel was refitted. Start by applying molybdenum grease to both sides of the breech block, and sticking one shim to the left side. This should slip easily between the breech jaws. You will need to centre the shim before inserting the breech bolt. I use a plastic chopstick, which is ideal because it is tapered, and being plastic there is no risk of damaging the thin shims. Replace the bolt just enough to hold the barrel in place, turn it over and slide in the second shim. With everything lined up, the bolt will thread in, before screwing the lock nut on. Be careful not to over-tighten the bolt; it needs to be just tight enough to inhibit any lateral movement, without any binding through the cocking stroke.
THE RIGHT CONNECTIONS
Now is the time to link the barrel to piston. Position the cocking shoe in the cocking slot, making sure it is the correct way round, reinsert the end of the cocking link into the shoe, before offering it up to the closed barrel. At this point, I want to consider the V-Mach removable cocking link pin, which we are about to use.
As has already been established, the fitting of a removable pin means that the cocking link can be extracted without removing the barrel, which has particular benefits for reassembly and also future barrel changes. The pin that
Steve Pope at V-Mach makes consists of a machined pin, with a flat rivet-style head on one side, internally threaded to accept a small countersunk hex-head screw on the other. All that is required is to insert the pin, and lock into position with the screw – very simple, yet very effective.
The pin itself is made from a harder material than the original rivet, so will resist wear for longer, and is made to a higher degree of size tolerance, so will fit perfectly, and minimise the degree of rattle, sometimes heard at the breech block. The pin needs to sit very close to
With everything back together, it’s time to get on with proper testing.
Out with the old and in with the new. That new liner moves in and out of the piston.
Loosening the old liner, but taping down on a hard, yet yielding surface.