Tuning FWB 124 needing some love

[Crank]

Bought a 124 from an auction, it was clearly advertised as not working and wouldn't fire a pellet. So I had no expectations of what I would receive, but I did order up a piston seal and a new breech seal, knowing those would be definite needs.

Well, it showed up yesterday and externally in fairly good order for a 40 year old rifle. I pulled the action and that's where things were not looking so chipper. There was sludgy moly lube, rock hard oil varnish and it looked like parmesan cheese crumbs everywhere.

I noticed the pivot pin end where the lock screw goes, had a small section of the edge cracked off. The bolt/lug that holds the trigger didn't look seated. That would turn out to be from cross threading and being partially stripped out. 

When I pulled out the piston, everything was sticky and crunchy. Some of the varnish was so hard to remove that I used acetone and a stainless steel brush and resorted to scraping some areas. The piston cup was unrecognizable. The mainspring had a kink in it, but it straightened with minimal flexing. I scraped and scrubbed the piston tube, but I was lazy and didn't run a ball hone in it. I would regret that later....

Got things lubed up, ran a tap into the damaged threads to clean them up and put it back together. Fired a couple of shots and it seemed to have a normal amount of resistance cocking, but velocity seemed moderate. After about 10 shots, I pulled the trigger and the piston released and slowly went home. I monkeyed with it, kept testing and it seems that there is still crap in the tube, so I'll be taking it apart again. I'll get another spring ordered and I'm going to weld up the damaged threads and re-tap it. 

Oh well, I was hoping for a minimal refresh, but it looks like I'll have to give it some extra loving to put it right. The downside is I'm going on travel and this will have to wait until I get back. Such is life.

Mark

 

[Motorhead]

Getting all that waxy dead seal that gets pounded into the roof of compression chamber can be a chore !!! get it ALL OUT even in the corners !  Then 3 stone hone the chamber all the way up against the chambers roof. The ARH seals require a perfectly flat and debris free chamber wall all the way to the roof ..... heed this advise please.





Scott

 

[Crank]

Scott,

I hear you loud and clear. When I scrubbed, it appeared that the forward face of the chamber was clean with the exception of some staining, but I must have missed some on the cylinder walls and probably right at the forward junction. When I was done cleaning, it looked like the factory used a mirror finish which seemed odd. The other thing that I thought had happened at first, was that the pellet wasn't seated deeply enough and was acting as a plug. I used a pellet seater and the pellet would come out at about 50fps. You can feel the piston move slowly and it just feels funky. Whatever it is, it makes that spring give it all to go forward. You mention a tri-stone hone, is that a personal preference, or does it meet a specific need? I use the ball style hones, since that's what I always used for shotgun chokes because of the surface finish I can get with various grits. I could make a scraping tool to verify the corners are completely chase out. 

Overall, it seems to be a nice rifle and ought to be fun once sorted. I can say though, I understand why more people opted for the Deluxe model, the standard stock has the ergonomics of a 2x4. I may commit heresy and do some reshaping after I sort out the mechanicals, unless I can source a reasonably priced replacement. 

Thanks again for the input.

Mark

 

[KWK]

Mark, give Paul Watts' video a look while it's apart. He delves into some other concerns that you are more than capable of addressing. Mark is quite the capable gun crank himself. 

I'm thinking about replacing the belleville washer in mine with a fitted delrin washer as Paul mentions. But first I want to make sure the forks are aligned. Wish I had seen his video before I worked on mine. I suspect the forks because I am getting some horizontal stringing. And I didn't check when I had it apart. I assumed it only needed a replacement piston seal. Mine didn't shoot when I got it either. The trigger was way out when I got it too. Now it's proper 2 stage and about as good as this trigger can be. And that's not too bad. I didn't like the color of the stock so I cheated and just rubbed it down with steel wool. Raised some minor dents. Then wiped some walnut oil stain over it. Two coats of rubbed out Tru oil and it came out waay better than I expected. And it was easy.. If you see the stock you can hardly believe it.. 

I didn't like the Beeman brake on it so I made my own sleeker brake. Too thin for set screws so I glued it on. No room for a sleeve in there. And no set screw marks on the barrel. Does not add to the barrel length either.

https://www.youtube.com/watch?v=93EhNKQqrKo

 

[thumper]

Did you size the seal? 

Two of mine had very undersized tubes, and one of them has a bad taper to the tube with the front being really tight. Neither make the power that others claim to get due to this. 

I had to size the ARH seals way down to fit right. If not they squeegee the lube out and get very tight and squeaky after shooting a bit and power goes down a lot. It's compounded with a shiny smooth seal and a shiny smooth compression tube. 

Also, good luck with the pivot bolt. They don't stay tight even when they are right. So if you have the ability, converting it over to something like Weihrauch or basically everyone else uses would be well worth your time. 

Have fun. 

 

[Crank]

thumper,

The seal didn't seem particularly tight and was no fuss going in, but that very well could be. Funny that you mention about squeaky, it did start off that way when I first cocked it. I wasn't planning on tackling it again before I leave, but I may tear it down just to get another look inside. Otherwise it will nag at me while I'm killing time in Japan.

The pivot bolt isn't trashed, but it got damaged at the end. My larger concern is the trigger housing with the knackered threads. That means TIG time to put metal back in if I want to do it right.

No matter what type of hone I use, it probably needs that shine cut back.

Mark

 

[thumper]

I thought the receiver threads for the pivot bolt were messed up, sorry I got my wires crossed up lol. 

While you have the TIG out, it may not be a bad idea to put a small tack on the bottom side of the detent lug in the receiver. They have a pretty small purchase area and it's just a press fit. May save it coming loose down the road, if you plan to keep it. No other real good way to fix it when it does. 

 

[Motorhead]

Mark,

Ball hones SADLY DON'T GO INTO CORNERS and the why for mentioning a 3 stone brake cylinder hone. These stones generally are right up against the hones carrier shoes. If not simply belt sand there ends so the stones are on the edge. That is the only way you can hone into the corner and make sure no poop from that old seal in stuck against the wall surface ( Which it generally is )



You can ball hone the cocking slot area of tube quite well tho.

 

[Crank]

Scott,

I understand what you mean and it makes sense. This thing was a mess and I'm not surprised.

Thanks

Mark

 

[Crank]

Well, I did two things. I thoroughly cleaned the compression chamber and for laughs, I reduced the piston down to dang near free fall tension. Running much better, a bit of vibration and driving a Crosman 7.9gr pellet at 670fps. The spring, I think, has seen better days. It came out kinked again, so my best guess is it probably could use replacement.

I feel much better now and can worry about this one later.

Mark

 

[Michigander]

Good discussion and thanks for the video link. I had an HW55 with remnants of the leather seal jammed at the forward corners of the cylinder and was able to remove the debris with an angled hardwood scraper. That might work here.

So far the M4 pivot locking screw on my Sport is holding after torquing to 30 lb-in and placing some mild Loctite on the threads. I had to loosen it after torquing to readjust the pivot and it squeeked pretty good so I think at 30 lb-in there is enough friction to keep it from vibrating loose. I have a contact at FWB and may ask him what the factory spec is for torque on that particular screw. At the factory torque the locking screw was holding and didn't loosen until the gun had been worked on.