Canadian Airgun Forum

ChrisK's link for 'the book' no longer works, so I had to search for it. I'm hoping it's the same file.

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B51
QB78
Crosman Phantom
a pair of 1377s
2240
.357
Sigarms 1911
Condor

Thanks guys.......Walter sent me the link so I'm away to the races. Can't seem to get enough 'ooomph' out of these old bones to get past 450psi so it looks like it's tear-down time........no problem as that was going to be fairly early in the process anyways so it might as well be now and I can get a handle on how this thing works.......and a little internal TLC while it's apart.

I think the 'tuning guide' already solved a small problem as the cocking lever was quite difficult to pull back...and there seems to be an easy fix available. Now...if I can keep track of all the 'bitty parts' this should be fun and interesting.

Thanks all - Gus

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"Political Correctness is a doctrine fostered by a delusional,
illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

Glad you got the file Gus.

tips:

remove trigger bits.... dollup of grease for springs.....

polish hammer section of tube, polish the hammer surfaces to a high polish, polish track in tube for screw #26 make sure no binding as hammer slides back and forth.

Lathe up a delrin hammer spring guide, Dremel a slot in hammer adjuster screw, setup hammer stroke for about 0.500"

fill to 2500psi for starters,

Loosen valve end cap before removing screws/pin, When reinstalling valve remove oring, thread cap on until gap is just wider than oring, roll oring into place, lube with silicone oring grease, push it into place, fasten with screws, pin and stock bolt/nut, ..... DO NOT FORGET TO TIGHTEN THE VALVE CAP

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Walter

You anticipated my next move Walter.......which was to ask for tips from those what "been there - done that"

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"Political Correctness is a doctrine fostered by a delusional,
illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

Just got home from the post office with my B51. This is one awesome looking rifle!! I'm glad I got the thumbhole stock because it feels great!

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B51
QB78
Crosman Phantom
a pair of 1377s
2240
.357
Sigarms 1911
Condor

Started the dissassembly. I must admit that my first impression looking at the schematic was.......a bit of information overload....but after getting into this thing it's turning out that it's really no more difficult than working on a QB78...everything is in there in a logical order and if the easy directions for the 'The Book' are followed it's a pretty simple process.

The breech/barrel assembly comes off like a dream and I'm quite impressed with the valve port design...a simple button with two '0' rings....I can see how this could lead to some interesting experiments with port sizes.

My initial observations were that (at least this gun) the gun was quite dirty inside. I see evidence of random bits of swarf in the fill cap '0' rings and threads and general grunge down the tube. The hammer already has a number of scratch's on it and Walter's suggestion that it needs to be polished is dead on...as well as his suggestion that the inside of the tube where the hammer runs could use some polishing and cleaning up. I also couldn't detect the use of any form of lube when the fillcap was installed. The two '0' rings are still in good shape (under magnification) but a bit of air tool oil will be used to assist in the re-installation process.

First thing to go is the safety...I remove all safeties on all my guns anyways...but this one goes because of the simple power adjustment mod that can be made.

Haven't got the valve out yet...that's next on the list and a close exam of the valve seal should indicate why it was leaking.

And now.........a couple of questions looking for answers

1) What would be the optimum transfer port size if I want to get a fairly consistent 900 - 930fps assuming that I get everything else in correct ballance? Or...just leave it at factory spec and adjust from there?

2) What is the valve seal made out of? Delrin? Just in case I need to make another one.

More to follow as the story develops

And.........there's the little rascal right there. At some point the seal face was hit or an orphan chunk of debris got under it. In any event, this seal was never going to .......seal. 'The Book', fortunately, suggests a fix for this that involves some 600 paper and a gentle 'turning' of the seal face against that in order to correct the problem.
I do notice that the seal face is 'cupped' and I'm not too sure what the result of making a flat lip is going to do.

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"Political Correctness is a doctrine fostered by a delusional,
illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

OK - that's got that done The fix from 'the Book' wasn't going to work as the indent in the seal face was much too deep - but a little trip to the lathe with a honed bit solved that in short order and retained the correct 'cup' contour on the seal face. Still a bit of a leak at 1000psi but a 1/2 dozen shots got everything back to normal and it's holding fine and now seated....... and what a HUGE difference in cocking - now butter smooth and almost effortless after 'glassing' up the hammer and de-burring and giving the interior of the tube a little polish.

There was, certainly, a lot of gunk/chips/swarf inside but some cleaning and a liberal dose of brake cleaner got rid of that.

I would certainly recommend that anyone buying one of these take it down just as a matter of course. It 'looks' like a complicated job...but it isn't (but, you DO need the right tools). Mods as described by Walter and 'the Book' are simple and effective and don't take much time at all. I'm also convinced that re-assembly is actually easier on one of these than a QB....and no problem with shaving '0' rings on the B51 if you take proper care.

I am a very happy camper and now to get the glass back on, throw some PSI to it and go have some fun

Many thanks to all for your guidance and suggestions - much appreciated.......and Walter - if I manage to make it out to a shoot I will certainly provide you with a ...or two.

Cheers - Gus

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"Political Correctness is a doctrine fostered by a delusional,
illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

Mine had no apparent leaks (no hissing etc.) but only held air for about 24 hours so I followed the writings in the tuning guide and stripped her completely. She now has new seals front to back (each one coated with Molykote) and she has been sat on my gun bench now for 4 days with no loss of pressure at all. A few simple tools and take your time and voila! done.

Now, if only the scope would arrive.

Cheers

DaveD

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"THANK YOU AIRGUN SELLER.........................................................SORRY MR BANK MANAGER"
"The bitterness of poor quality lingers long after the sweetness of a low price is forgotten”

OK, so I'm late to the party, but someone said better late than never.... I've finally sold off enough old projects to get permission from the better half for a new one.... I just paid sniper for a B-51 in .22 cal....

so now where can I get a copy of the "book"?....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!

Life is too short to be wasted worrying about the opinions of others.

see link next post below....

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Duke ))))----//----------==

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WOW!.... thanks for the quick response from four different guys!!!

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!

Life is too short to be wasted worrying about the opinions of others.

I ended up replacing the two screws that hold the trigger chassis with a r/c hex countersunk screw, because one of mine was stripped.
Part no. 31450 from Team Associated, in case some else needs or wants to replace theirs too. They come in a package of 6 for 2 bucks. I bought 3 packages, if any B50/51 owners wants a pair, PM me your address, and I'll send it to you.

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B51
QB78
Crosman Phantom
a pair of 1377s
2240
.357
Sigarms 1911
Condor

size and tread please i"ll borow some at the shop tomorow

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slavia 618
qb78 .177
crosman phantom .177 , Rex 2-6x28 (thank to lauchlin)this scope has died 02-02-2012
dasy 953 , ncstar 3-9x42 compact
crosman mk1
crosman quest 500x

M3X5mm Flathead countersunk

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B51
QB78
Crosman Phantom
a pair of 1377s
2240
.357
Sigarms 1911
Condor