B51 stuck end cap removal

[wham bam51]

My b51 has been sitting for many years. I started to tear it down and discovered the cylinder end cap is very badly stuck. I dont have a vise at the moment so that creates a def problem lol. I was thinking of filing two small flats on the cap to allow for a wrench. Would this create a potential hazard when the cylinder is pressurized. also I wondered about the air hole in the cap. Is the size critical? The only real reason i need it removed is to get the valve out. I thought maybe i could drill the hole slightly to allow for a small rod to push the valve out.

[bubba zanetti]

Just to make sure, you mean the black end cap that covers the fill nozzle? That is what is stuck?

BZ

[wham bam51]

Sorry my bad. its  the cap that holds the fitting for filling.

[bubba zanetti]

Believe it or not the fill cap on mine is so tight it has served as the method of the whole cap assemblies removal (silver part). A wrench fits on that so easy. Also, it helps if there is no air in the tube.

Since you are doing a total rebuild. I would ensure no air in tube. drip some Kroil (its a really good penetrating oil) on the seam between the silver end cap and air tube, let that sit for one or two days, then try and remove it.

If that doesn't work, I have another idea that can be done. Lets try that first.

Patience Grasshopper.

BZ

[Ribbonstone]

Be sure it's really really empty.   

I won't even try the front end cap until I've gotten the rear end cap off/striker system out, and can work the valve in and out with a dowel.

If you got the fill nipple off separate from the end cap, then can be pretty sure it's empty, but the cap itself doesn't have wrench flats


After time,they can really get stuck...either they were screwed down by angry Pandas or the or0ngs have swollen and hardened.


Take a bit to put together some pictures...be back.

[wham bam51]

Yes it is def empty. The rear cap, hammer springs etc have been removed.Sadly i discovered another issue. It seems when the gun was assembled the tip of an allen wrench broke off in the head of one of the screws that holds the trigger block on. The only way to remove it is by drilling the head of the screw off. I thought i might luck out and remove the good screw and spin the block to remove the bad screw but it only loosened it. So i can neither re tighten it or remove it. My only option is drilling. Off to a frustrating start for sure.

[bubba zanetti]

The screws on the BAM are pretty soft. So drilling should be pretty easy. The good news is the screw sizes are in "The Book of the BAM 50" right at the beginning in the parts diagram. All metric and nothing really odd.

Try the Kroil, a little goes really far! Then put a wrench or socket on the fill nozzle and see if that will remove it. Again, if the fill nozzle starts to loosen I have another idea.

BZ

[bubba zanetti]

Here it is:

https://www.lebedev.com/airgun/technical_details_for_adjusting_the_bam_b50_51.pdf

BZ

[Ribbonstone]

flickr problem...try again.

[Ribbonstone]

Not a BAM expert....lot of people have studied them in much more detail when doing mods. I just kept this one running and learned how it screws up.

Yep...they should have put flats on the fill cap.  Sooner or later are going to want to seperate the nipple and the end cap...and likey don't have a little strap wrench.

Probably didn't put flats as they were using it for the set screws of the barrel band and wanted it round.  Nipple cover would work with flats on the fill cap, but the band set screws  might not (would have had to make sure the treads were indexed just right to have the band set screws end up where there were no flats).

Any way,with luck (or when you put it back together and back on) will come on and off by turning the tighted fill nipple.   

DSCN2752 by Robert Dean, on Flickr

NO good reason for this long threaded end cap to have to be crazy tight.  Been using it for years just firmly screwed down.


BUT if you absolutly had to...and were willing to do a little hidden ugliness....could file two flats on the end cap.  Can see the set screw marks, so don't make a wrench-flat there.  The nipple cover will still work and hide the flats.

DSCN2753 by Robert Dean, on Flickr


Nippe is usually sealed with a Dowty seal. They are tough seals,but they will wear out/harden up eventually.

While the fill end cap is off,look down the bussiness end.   

DSCN2757 by Robert Dean, on Flickr

There is a little filter.   On the otherside of that filter is the fill nipple check.  Sudden pressure (like tank filling an empty air tube) can push that nipple check back hard enough to push that filter out/crack it.

Slow filling generally just bows it a little (like the one shown, it's kind of  "dome"shape).

OLD PCP PROBLEMS:...not just a BAM problem. ALL PCP'S set up like this used in wet enviroments will show this after some years of not being taken apart.

Looking at the above pictures, everything from the two sealing o-rings to the left  lives in the pressurized area of the tube.  Whatever happens there is from the fill air.

Eveything from those two sealing o-rings to the right is in a non-pressurized area.

A rifle used in the rain/mist/serious humidity will often show rust in the end cap threads.

It's not from the air filling the rifle, it's from the outside air wicking  moisture down the threads to the o-rings...where it kind of sits, unable to evaporate quickly.

Expect rust there....which makes the threads a bit crusty...making unscrewing the end cap more of a PIA.

Sorry for the crappy picture....can make out that the threads and tube are a little crusty.  Looking at the end cap enlargment above,can see some of that cursty still in the bottom cap threads.

DSCN2755 by Robert Dean, on Flickr


(Clean it...silicone grease it heavy....problem won't repeat....just use "real"siliconew gease, not something with petroleumas part of the mix.)

Can find the same type of rust problem  on rifles that use a gauge block/through the air tube gauge.  Everything between the o-rings on the gauge block is ouside air.

[wham bam51]

Thanks guys for all the great info. I figured filing flats would be fine. Just wanted to double check. As for the messed up screw on the trigger block its more of a pain. I normally would sign out a drill press and vise from my local tool library but it is still closed due to this dam pandemic. It will take a bit more head scratching to due with the tools I have on hand.

[Buldawg76]

Another option would be to drill holes where the barrel band set screws leave an imprint in the end cap about 1/16" deep much like the hammer spring end cap has done on it. Then get longer set screws for the barrel band so that they will snug down into the drilled holes to secure the band to the end cap and allow the band to be used as a wrench of sorts to loosen the cap threads.

The only issue with this method is in the future you will need to secure barrel band to end cap and rotate the band cap assy to center band on barrel before filling cylinder because the drilled holes will limit movement of barrel band for centering on barrel and once filled with air you will not be able to rotate the end cap/barrel band to center on barrel.

BD

[wham bam51]

Success. I used some blocks of wood and c clamps for a makeshift vise. I was able to remove both the end cap and the trigger block. There is some very minor damage to the threaded hole that the trigger block screw was stuck in but im confident that a gentle run through with a tap will clean it up fine. There was no rust on the end of the cap or inside the cylinder. Over all nothing to terrible. The valve has been modified and  will need some tlc. I will need to order a replacement belt for my little lathe then I will be able to get on with some work. The thumb hole stock is not my cup of tea so there is some work to be done there as well.

[bubba zanetti]

Success. I used some blocks of wood and c clamps for a makeshift vise. I was able to remove both the end cap and the trigger block. There is some very minor damage to the threaded hole that the trigger block screw was stuck in but im confident that a gentle run through with a tap will clean it up fine. There was no rust on the end of the cap or inside the cylinder. Over all nothing to terrible. The valve has been modified and  will need some tlc. I will need to order a replacement belt for my little lathe then I will be able to get on with some work. The thumb hole stock is not my cup of tea so there is some work to be done there as well.

Excellent

[Buldawg76]

Success. I used some blocks of wood and c clamps for a makeshift vise. I was able to remove both the end cap and the trigger block. There is some very minor damage to the threaded hole that the trigger block screw was stuck in but im confident that a gentle run through with a tap will clean it up fine. There was no rust on the end of the cap or inside the cylinder. Over all nothing to terrible. The valve has been modified and  will need some tlc. I will need to order a replacement belt for my little lathe then I will be able to get on with some work. The thumb hole stock is not my cup of tea so there is some work to be done there as well.

 

BD

[mackeral5]

Congratulations on getting it apart and no collateral damage. 

Thank you all for sharing BAM tips and tricks.  I'm soaking up all I can while I impatiently await the shipment from Canada.

[wham bam51]

I have found another potential issue with this gun. When the barrel band is removed. The barrel springs down until it is touching the end of the cylinder.If the band is forcing the barrel up then would it not be bending the barrel?

[bubba zanetti]

I have found another potential issue with this gun. When the barrel band is removed. The barrel springs down until it is touching the end of the cylinder.If the band is forcing the barrel up then would it not be bending the barrel?

Mine bends up a little when the band is off, sort of banana 🍌 ish  .

I don’t shoot it with the band off so I’ve never had an issue with pellet FPS issues or accuracy, when it’s shooting right.

Welcome to BAM ownership.

BZ

[wham bam51]

Ya when i take the barrel off and check it with a straight edge it appears straight, my straight edge is too big to fit when the band is on so i will try to find something that I can check it with. I am toying with swapping to a .25 barrel but haven't decided yet.

[Ribbonstone]

BAM barrel band:

BENT BARREL is certainly possible....everyones first suspect.

Check the barrel. Don't want to take the barrel out of the reciver (it's glued into the reciver),so a straight edge test rather than a roll test.

Check the air tube to be sure it's straight (although I'd bet 99.9% of them are).

If the barrel does prove bent...well...it's already bent....un-bend it.

IF IT BARREL AND TUBE CHECK OUT STRIGHT:

IF the barrel is pointing "up" (not allowing the band to go on unless you press down on the barrel), then my first sustpect is the transfer port being high/cocking the reciver upawards.


If the barrel is pointing down,then I suspect something is cocking up the back of the reciever.

OK...expaination...basically the "long lever" idea.

Receiver (breech) is sharp edged where it joints the air tube.Not like knife sharp, but I could peel an apple with it.

A burr on one of those edges could cock/rotate the breech a little to one side.

A little burr at the rear end of the breech could cock the tip of the barrel down.....a little burr at the front end could cock the barrel "up".

This is the "parts gun" (actually has gotten a lot of post as a parts gun in the last few days,becasue I never fixed it/tightend everything down).

1. Barrel checked out stright.
2. Tube checked out striaght.
3. Barrel still pointed "down" at the barrel band. Could get it in place by lifting (bending) the barrelup just a bit.


So I check the tube and the breech for burrs high spots.

Check the "knife"edges of the breech ... one burr/dent/ding there could cock-eye it, two burs at the front could cock it UP ..two at the back could cock it DOWN

ON this example...found 2  things....an odd little high spot between the two rear reciver screws and burrs at the screw holes.

Can barely see it...can barely feel it...but it'sa long lever wehre a tiny bit of difference  makes a big bit of difference at the muzzle.

Looks like "nothing"...hardly noticable....but it's a LONG azz leaver with a real short folcurm.

DSCN2760 by Robert Dean, on Flickr

Can see the screw hole burrs and the "mystery lump" better once polished down.

DSCN2762 by Robert Dean, on Flickr

Started like this (with those little burrs/bumps):

DSCN2763 by Robert Dean, on Flickr

And ended like this (without the burrs/bumps):

DSCN2764 by Robert Dean, on Flickr


LIKELY take down/assembly over the years made the screw hole burrs....or any receiver edge dings....the "mystery hump" seemed to be factory.