Why does my 2100 lose power?

[Rex]

Bought a 2100 about two years ago and really enjoyed it for nine months.  Then it was too easy to pump.  Got a Chrony and found the Muzzle velocity was below 500 fps.  Like the gun enough to reseal it with new gaskets, pump cup and piston.  Velocity came up to a disappointing 520 fps.  Bought a new one and darned if the same thing didn't happen, only sooner.  Any explanations, wild guesses or conspiracy theories would be appreciated.

[pelletpusher]

Did you replace all the seals an o-rings.I assume there's an air valve like a 1377 inside with
an o-ring on it. If the oring, pump cup, or both are not sealing, no pressure buildup.
Did you use any experimental lubrication that would damage the seals?

[Rex]

All those parts were replaced new (some twice) and I used Crosman Pelloil and non-detergent WD30.  A good dose of oil will get the muzzle velocity up for one shot.  The pump cup and valve assembly O-ring were obvious suspects, but changing them out didn't help.  I wrapped the valve check body threads with Teflon tape for a tighter fit with no positive results.  I'm just not sure where to go from here.

[pelletpusher]

Those threads on the valve aren't npt, I use blue thread Locker I don't trust the tape that's a
lot of pressure. Do you pump then cock the bolt or cock then pump try both to see if there's
Any difference in velocity. It sounds like low compression but leaks can play havoc. Easy
Pumping after 3 pumps usually means the seal & cup is failing bad.Also putting oil in & seeming to help
 Is a sign.
when you get to 8 to12Pumps with good seals you'll have felt the compression build & top out, now the seals have
reach their limit.
When I was a kid we would use motor, chainsaw bar oil,&grease. It's possible the oil
ruined the seals it self or by gaining more compression with thicker fluids over worked
Them thus making them short lived.
As of right now I'm using moly engine assembly lube it's slick semi-thick & stringy, seems
To do well, as for the seals time will tell.

[Rex]

Lots of things to think about and work on.  I'll give them all a try.

[K.O.]

All those parts were replaced new (some twice) and I used Crosman Pelloil and non-detergent WD30.  A good dose of oil will get the muzzle velocity up for one shot.  The pump cup and valve assembly O-ring were obvious suspects, but changing them out didn't help.  I wrapped the valve check body threads with Teflon tape for a tighter fit with no positive results.  I'm just not sure where to go from here.

Did you use wd 40 before rebuild...

If so it dries to a yellowish sticky and Hygroscopic mess.

Did you Inspect pump tube...

Do you store with a couple pumps to keep cup expanded...

will it hold air overnite...

Can not understand why no wiper for oil to me they seem to need a drop every 20 shots or so before you are dry pumping dry pumping.

the old 2100s had a better piston the new ones are one long floppy plastic piece I am going to stuff mine but as long as it is it may not help.

It does help the short 1322/77 piston.

Look at page 8 then look at yours I do not know when they changed but mine is a may 2011 and is plastic the whole way...

http://www.mp661k.com/sitedocs/13xx_HotRod.pdf

[Big Bore Bart]

  It sounds like there is a burr in the pump tube that is cutting an O-ring, or the pump cup. Check the pump pivot holes and the slot, a sharp edged slot will kill a cup in no time. The only thing needed on the valve threads is the O-ring.   Check to see if the valve has set back into the stop detent, aluminum valves give out at the bottom where they contact the stop.
 Thinking of the differences between a 2100 and a 766.    With the 2100 the barrel can be installed slightly off center (unlike my 2nd var. 766).   Check the wear on the bolt, the bump on it is the only form of seal at the breech.   You can cut a 7mm od X 1.4mm deep recess in the barrel and install a 7mm X 1.5mm O-ring, it will then seal like the M-Rod.

[K.O.]

I feel that maybe the lack of a wiper is going to wear out pump cups on a lot of  2100s and 1377/1322s.

Here  a  B.B. Pelletier review stated velocity went from 690s down to 620 rather quickly...

https://www.pyramydair.com/blog/2012/01/crosman-2100b-multi-pump-air-rifle-part-2/

I know I will try to add a form of wiper when trying to stiffen the piston with 1/8th rod.

[Rex]

I just verified that the tube slots had not been deburred.   A pocket microscope verified the damage to the O-ring.  I'll clean it up and try again.  I wonder if wipers are still available for old 2100/2200's  and would they work?

[Big Bore Bart]

Yes one would help.  Some places might still have the foam rings, the felt you will probably have to make.  You could possibly do a leader wrap, and use some wool yarn for an oil ring.   After deburring the tube slots, ensure the pin holes are also smooth.

[mav72]

I just verified that the tube slots had not been deburred.   A pocket microscope verified the damage to the O-ring.  I'll clean it up and try again.  I wonder if wipers are still available for old 2100/2200's  and would they work?

Got here too late... Was going to suggest that... I got all my parts from an old shattered 766... I don't know when they started putting plastic pump pistons in the 2100...

[Rex]

I'll definitely keep my eyes open for a junker 766 - maybe ask a collector/fanatic I've done business to look out for one.