Friday, January 22, 2010

A NOS Weihrauch 35 E Gets an Overhaul Part 2

Back at it today. Looking for a tighter spring fit inside the piston. There's about 0.106" of play between the stock spring and the piston ID. Way too much gap. The spring will rattle your teeth with this kind of room. Shimming the inside of the piston will be necessary if I use the original HW spring and I'd like to avoid that this time around.

I found a couple other springs in my parts box. The first is 0.946" OD with a wire diameter of 0.156". The second option is 0.943" OD with a 0.137" diameter wire. Both are 9" OAL--exactly the same length as the stock HW spring.

I'm not sure which spring to use. The first spring option might be more powerful, but the second option is lighter and may accelerate the piston faster. I'll try the second, lighter wire spring first. If it doesn't work out, I'll only have to reduce the diameter of the spring guide to fit a different spring.

First, I need that new spring guide.

Chucked a piece of delrin in the 3-jaw and the steady rest.

Faced the end off.

Rollers on the steady rest. Lot of overhang. The rest helps keep the work from deflecting.

Spotted with a center drill

The delrin machines well.

Drilled through with successively larger drill bits finally ending with a 25/64". The piston rod just fits through the hole.

Turned down the OD of the guide to 0.663"

Lathe power off. Test fit the spring on the guide. Snug, but not a struggle to install. Left a wide flange at one end of the guide. The base flange is 0.752" diameter and 0.139" thick.

Scrounged a big chunk-o-scrap steel to make a custom washer for the base of the spring guide. After facing it off, I cut a slice about 0.25" thick.

Reversed the jaws in the 3-jaw chuck and grabbed the outer edge of the washer. Faced, spotted, drilled.

Sorry, it's blurry. Used a small boring bar to bring the center hole to about 0.666". The spring guide just fits through the hole. I made some relief cuts to recess the flange at the bottom of the guide as well as recess the front of the washer inside the piston.

Piston, mainspring, and the 2 piece guide. The guide ended up at 4.175" long OAL. Pretty much the max that will fit into the 35 E piston. Full spring support = no more kinked springs.

The most current Weihrauch spring guides are made much the same way--delrin with a substantial steel washer.

I was concerned that the base washer was too thick and wouldn't allow enough of the piston rod to protrude. If that happens, the trigger can't reach the notch and the gun won't cock.

The beveled edge on the washer fits inside the piston body. It's now only a few hundredths thicker than the stock spring guide. Test fitting looks promising. The washer is 1.172" OD and 0.193" thick. The leading edge was turned down to 1.012" to fit into the rear of the piston to a depth of 0.053". The rear of the piston has a slightly beveled inside edge and I made a slight taper to the washer. The end of the piston and the top of the base washer should now self-align when the gun is cocked.

The bottom of the washer is countersunk for the end of the delrin guide. The mainspring will push against the steel base--which in turn is directly supported by the massive steel end cap. The delrin guide has good lubricity both to the spring and to the piston rod.

I still have no idea if this spring is a good choice. Every choice seems to compromise something else. I think that the gun would benefit from a lighter piston, but I'm afraid to just start milling slots to reduce the weight as there's concern that a lighter weight piston will tend to bounce at the end of the compression stroke... Don't let anybody tell you that tuning a spring gun is simple. I want this gun to go "thunk", have no vibration, and deliver an RWS hobby in the 730+ fps range. As always, I'm willing to compromise some speed for mechanical smoothness.

Need to reassemble it and set up the chrony next.

A NOS Weihrauch 35 E Gets an Overhaul Part 1

Nick has been posting like a fiend lately. I think he's making up for lost time in December. I've been on an acquisition spree of late--Walther LG 55, Crosman MK2, Sportsman QB77 and this--a new, in the box, .177 cal Beeman/Weihrauch 35 EB from 1985. The model 35 has been in production since 1951 and incredibly, it's still available today. Until the introduction of the Feinwerkbau 124 in the 1970's, the 35E was one of the most powerful airguns in the world.

Beeman used to sort the guns. For a small premium, you could get a nicer stock, less barrel droop and/or a gun with a better test target. This one indicates on the end of the box that it has a "select group" meaning that the test target was in the top 10% for accuracy. That "EB" suffix? I think that the "E" refers to a more expensive stock with a raised cheek piece, while the "B" certainly stands for "beats me?"--It may refer to the barrel length.  The box was postmarked in December of 1985, so I was a sophomore in high school. UPDATE: My Weihrauch expert, Volvo, tells me that the "E" simply stands for "export". Thank you, sir, for the correct info!

Typical Beeman packaging. Volvo also noted that Beeman sorted and re-boxed the HW guns like this then double boxed for shipping. Odd, since this box has a postmark on the outside. Gun is pretty well supported in the box and difficult to remove. While it's probably considered collectible in this condition, they're still available new. This one has a serial number of just over a million.

Extra front sight inserts are hidden under the hang tag.

The guns are packaged with a factory fired test target that is serialized to the gun.

There's no chisel detent for lock-up--it's an old-school barrel latch. Press the lever forward to unlock. It's smooth and positive. The notch in the stock is necessary to allow clearance for the latch while cocking. I can't think of another current production rifle with a latch. A seriously cool feature.

Ah, the Rekord trigger.

Not a bad chunk of lumber considering this isn't a "select stock".  Doesn't look like the beech stock I expected. This is a piece of European walnut.

I fired the rifle a grand total of 3 times before setting it aside for a few days until it could be overhauled. The vibration, rattling, twang, noise, smoke--did I mention vibration?--was likely the result of 25 years sitting on a shelf. Sorry, nope, no chrony data. I found some time this morning to begin the rebuild.

Removed the trigger guard and the forend screw. Note the lack of a cocking lever slot in the forend. The rifle uses an articulated cocking linkage. The HW 50 was another classic with that feature. In theory, there is less stock vibration.

Mainspring looks really dry.

The articulated cocking link has a small housing that keeps the lever parallel to the compression tube while cocking.

Anyway, once the stock was off, I removed the sights and knocked the 2 pins out that hold the Rekord trigger unit to the tube. Used a small brass drift. Trigger comes right out. There's no trick to it at all. The safety and spring pop right out once the trigger is removed.

No grease on the mainspring, but plenty in the trigger. At least HW greased the trigger where it mattered. The sear contact is loaded with it--but it's old and waxy. Used some spray degreaser and Q-tips to remove all the old waxy goo.

Ended up here. Cleaned and lubed with a bit of moly grease on the sear.

Dropped the gun into the mainspring compressor and started to unscrew the end cap.

That's it. No pressure left from the spring. About 2"+ of spring preload.

Spring, spring guide and the giant end cap. The spring is 9" OAL and has 27 coils of 0.144" wire diameter. It's approximately 0.909" in OD. The spring guide is noticeably undersized at 0.552" diameter. That's just, uh, fantastic. The guide rattles inside the spring and the spring rattles inside the piston bore. Guess that's why they used to use an entire jar of moly on airgun tune-ups. Took up the slop and acted as a damping medium.

The end cap is absolutely massive compared to that on most spring piston guns. The end cap weighs 13.7 oz. Over 3/4 of a pound of steel. Remember Beeman's "Tap the Cap"advertising?

Polished the front end of the cap just enough to take off any high spots.

The spring guide seats against this end. A smooth finish may allow some guide rotation to help cancel spring torque. It's sure not gonna hurt for 2 minutes on the buffing wheel.

Removed pivot locking nut on the right side and the lock washer.

Then unscrewed the pivot bolt from the left side. It helps to break the action to take the pressure off the latch (or detent if it's a typical break barrel) then remove the pivot bolt. Otherwise, the bolt has some pressure on it from the latch spring.

Pulled the bolt free and fished out the razor thin pivot washers. One on each side between the breech block and the tangs on the compression tube.

Another pic of one of the pivot washers. There's the barrel latch.

The breech block came free and the barrel latch fell right out. Note the spring in the block that presses the latch rearward for lock up.

The barrel cocking lever assembly came right off. Fished the round end of the cocking lever through the hole in the compression tube.

Only the piston remains inside the tube.

Hooked end of the piston rod with a flat blade screwdriver and pulled it from the tube. Wiped off the grease and here it is. Older HW 35's use a leather piston seal. HW 35's with serial #843636 and higher use the synthetic seal.

The small circle on the face of the piston seal is from the transfer port hole. 25 years of pressure will do that to you.

Pried the seal off the piston head. Still feels pliable and has good elasticity. It also appears to match a spare Beeman R1/HW 80 seal found in the parts pile. I'll use it in the reassembly and see how it shoots.

More coming soon.

Thursday, January 21, 2010

Crosman MK2 Small Mystery--Solved!

Tracked down a very nice Crosman MK2 from Wayne last week. It just arrived a few hours ago. A quick examination reveals that this gun isn't stock. Somebody's paid some attention to this one.

This MK2 (.177 cal) was made sometime after 1975 based on the 9-digit serial number.

Loading bolt and knob are absolutely not stock and appear to be made from stainless steel.

An extended and thinned bolt nose. What's the story here?

This gun should have had a magnetic tip to work w/BB's or pellets. Obviously, this is set up just for pellets.

The knurling is extremely well formed on the knob.

The 30 or so shots I fired tonight (and I still haven't replaced the CO2 cartridge in the gun) were pretty darn impressive if this is a BB/pellet compromised barrel. The 9 and 10 ring are completely torn out of the target. Need to get some chrony numbers--no time for that until later this week. My wife came downstairs and wanted to know what rifle I was shooting it's so loud on full power.

Trigger was set to the lightest adjustment. Even a fraction of a turn lower and the high power won't hold on the sear. Obviously, it's been set up for target work. Wonder if anything else has been done to it internally?

So who made the loading bolt? I wish I knew who Wayne got it from. Anyone recognize their work? Ya done good!

Update: I did some internet sleuthing and found that the machinist was Mark from Iowa. Mark, absolutely first rate work here. If you want your last name used, just say so. He turned the part on a Mazak CNC lathe.