PS Magazine - TB 43-PS-721

PS, The Preventative Maintenance Monthly

ISSUE 721

DECEMBER 2012
PS Magazine - TB 43-PS-721 - Page 4 of 33
4
PS 721
DEC 12
Seems quite a few howitzers have been found with loose muzzle brakes lately. That
can result in damage to the muzzle brake key. While that’s not necessarily a safety
concern, a damaged muzzle brake key can eventually damage the thrust collar teeth
because of looseness or vibration.
To check for a loose muzzle brake,
grab hold of the lunette and towing
eye and try to move the muzzle brake
up and down. If you notice any free
play, look closely to see whether it’s
the towing eye or the muzzle brake
that is moving.
If there’s no movement at all,
you’re good to go. If the towing eye
is moving, make sure its long nut is
properly torqued to 350 lb-ft.
If it’s the muzzle brake that’s loose, you’ve got some work to do.
1.±
Use a set of side-cutting pliers to
remove the lock wire from the locking
key’s mounting bolts.
2.±
Remove the locking key’s bolts using
a
9
/
16
-in socket wrench.
3.±
Lift out the locking key and check it
for damage. Replace a bad locking key
4.±
Use a spanner wrench to loosen and
free the thrust collar from the muzzle
brake.
5.±
Make sure the muzzle end of the
cannon tube is visible to centered in
the witness hole of the muzzle brake
and the towing eye is at the 6 o’clock
position. Then insert a 4”x 4”x 8’
timber, NSN 5510-00-220-6178, into the
end of the muzzle brake to support it.
6.±
Insert the muzzle brake alignment
tool into the muzzle brake to keep it
from rotating.
7.±
Rotate the thrust collar
counterclockwise until it contacts the
muzzle brake.
8.±
Using the spanner wrench, tighten the
thrust collar while rocking the muzzle
brake up and down with the wooden
stave. Continue tightening the thrust
collar until all play is gone from the
muzzle brake.
9.±
With the muzzle brake alignment
tool still installed, slide the key down
to align with the teeth on the thrust
collar. You may need to tighten the
thrust collar a bit more to align it.
Never
loosen the collar to get it
aligned.
10.±
Remove the muzzle brake
alignment tool.
11.±
Apply CLP to the muzzle brake
locking key and insert it so that the
teeth on the key line up with the
teeth on the thrust collar. Don’t force
it or you’ll damage the locking key! If
the locking key won’t go in, reinstall
the muzzle brake alignment tool and
repeat step 9.
12.±
Remove the timber.
13.±
Install and torque the bolts to 30 lb-ft.
Undamaged bolts can be reused.
14.±
Lock wire the front mounting bolt to
the key. Then lock wire the two rear
mounting bolts together.
M777A2 Towed Howitzer…
Find the
Key
to Loose Muzzle Brake
make a note of
this
new procedure
until it’s added to
the Ietm.
operators, if you haven’t
checked for a loose muzzle
brake on your m
777
a2 howitzer
lately, now’s the time.
Cut away lock wire
and remove locking
key bolts
Locking key
damaged?
Replace it
Push up and down on towing eye
to check for movement
why so down,
mr. howitzer?
if
your
muzzle
brake was this
loose,
you’d
be down in the
dumps, too!
721 04-05.indd
1-2
11/6/12
11:20 AM
Click here for a copy of this article to save or email.
Back to Top
Back to Top