NEC­ES­SARY AD­JUST­MENTS Ger­many meets Amer­ica, as the Weihrauch HW98 gets its new in­sides

Airgun World - - Swapping To Synthetic Seals -

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.


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.


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.


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.


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.

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