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broommaster2000 · Moderator

Hear hear! Count Slav strikes again. Exclamation

Roy · Veteran Member

Glad to see that you are using the proper colored blinder.

Slavia · Moderator

Slavia · Moderator

What a piece of junk!

I got the gun in the box a few years ago in the "Bargain Cave" at Cabela's (meaning returns). I messed with the sights a little, but never went inside. I estimate that I put about 200 rounds through it, and then put it away as a future project gun.

Either the previous owner tried to get inside, or Mendoza has some real gorillas - these are the two screws that fasten the trigger assembly:

Here's what I found - the spring broken at both ends, with the pieces neatly coiled together:

I don't recall any sudden change in performance, so my best guess is that someone broke it, attempted to fix it, and then returned it.

Another interesting surprise - the hook that engages the sear is visibly turned with respect to vertical:

I'm not sure how that will sort out, since it looks like it's pinned together at the front:

The felt oil wick is broken, but I'm not too worried about that - it probably isn't necessary. If it serves the purpose of retaining that pin, then I can make something. The seal looks to be in good shape.

I also noticed that there is no barrel pivot screw - just a pin drifted in place. They probably adjust pivot tension by squeezing the yoke together. This I can fix.

So a few questions for you guys:

1. How do I contact Crosman to see if there is a replacement?

2. I am under the impression that the RM series (RM177/RM277/RM377, etc.) are all the same gun with different strength springs - is that correct? I found a non-Crosman supplier that lists a RM377 spring.

3. I measure this spring at: O.D.=0.792"/I.D.=0.545"/L=12.25"/41T. Anybody know of something similar?

cw · Banned

I serviced a BAM last year that had one end of the spring
broken. The weird thing was, that despite being 200 fps
slow, it was actually quite accurate.

Slavia · Moderator

I think in this case the short stubs that broke off screwed themselves into the main part of the spring and made "reinforced" ends of a sort.

I was wrong about the broken felt wick. PyramidAir has replacements that are split like that new.

Roy · Veteran Member

I'm amazed that the broken spring was not evident during shooting ; you'd think it would make an alarming "crunching" sound or something.

Slavia, how much did you pay for this rifle ? Not much I hope. But the good thing is that a new spring is really the only part you need to buy. The other parts can be fabricated.

I like that rear sight. Reminds me of the Beeman(Williams) sport aperture sight. Where did you get that rubber eyeshade ?

Slavia · Moderator

jonathan · Member

Where can I get that butpad? I used the same stock on my QB78......and I would love to add one of those.

Slavia · Moderator

Slavia · Moderator

The barrel pivot is a simple pin - no adjustment possible (yet). It's not even in there tight; I pushed it out by hand. The other hole is for the latch, also a pin. Instead of having two opposing chisel points, this has one chisel point riding on the pin. Actually not a bad idea, since the pin spins when it latches giving it a smooth feel:

The only wear marks on the piston are at the top rear. This is just where you would expect to find wear, given how the cocking arm pushes on the piston. The seal must be doing a good job of centering the piston in the front - no wear visible. The compression tube I.D. measures 1.004" and the piston O.D. measures 0.982" which leaves a gap (when centered) of 0.011"

I'm thinking of going to the local welding shop and having three puddles of brazing rod put on the rear of the piston to fill in that 0.011" gap (after smoothing).

cw · Banned

I never have cared too much for buttoning pistons
because of durability issues. So I, like you add
material (I prefer the wear characteristics of steel) onto
the piston skirt and then turn it down so that the piston
has a nice, tight fit in the compression tube. Buttoning a
piston provides only a few, very small, plastic (as opposed
to steel) bearing points for the piston to ride on. Plus, Over
the years, I have seen several guns where buttoning has
ruined the compression tube, by wearing grooves where
the contact points slide along it. The piston seal then has
a hard time following and sealing the piston against the
compression tube wall contours.

Slavia · Moderator

If I take your meaning, you're advocating adding material in a ring all around the piston skirt, rather than dots - correct?

What do you think of (softer) brazing rod vs. (harder) welding?

Macarri sells "old school buttons" (glue-on), and I suppose I could go to the trouble of drilling and fitting delrin, but neither solution seems that durable to me.

cw · Banned

Weld a .75"-1" band around the head of the skirt and
one around the base of the skirt. Don't temper it though
as you want the piston to be equal or softer in hardness
than the compression tube. It is more desirable to have
it be the consumable part for obvious reasons.

Slavia · Moderator

See this discussion regarding buttoning pistons:
http://www.airgunhome.com/agforum/viewtopic.php?t=2210&postdays=0&postorder=asc&start=0

While I'm resolving the spring issue, I decided to attack the piston. A 0.011" gap all around the piston seems pretty sloppy to me, so I thought I'd try buttoning. From that previous conversation, here's what I gathered:
1. I wanted to stay completely away from synthetics. I just don't trust the durability of either the material or the adhesive.
2. I would only "button" the skirt of the piston, as the seal holds the piston centered in the compression tube. This is borne out by the absence of wear marks at the piston's head. I don't really care about increasing power, but consistent piston positioning (and therefore consistent sear engagement) appeals to me.
3. The buttoning material should be softer than the compression tube, so that it wears faster (and can be renewed) than the compression tube (which can't be renewed). The buttoning material should go all around the circumference of the piston, so as to not wear "troughs" in the compression tube.
4. I knew I'd have to do this by hand, since I don't have access to a lathe. (The piston isn't round anyway.) For that reason I chose brass brazing material.

I had the local welding shop goober on the brazing rod:

And then filed it down:

Using measuring calipers, I worked the band down to an even wall thickness, and then filed around and around until it would just enter the rear of the compression tube. (The compression tube is flared slightly at the end.) Then I switched to single strokes with a diamond file, using a permanent marker to identify the high spots (rub marks through the ink).

Just before I install it I'll hit it with a buffing wheel, both to polish as well as to relieve the square edges on the brass band.