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Gamo Compact Leak

Discussion in 'Technical' started by Clive Jones, Nov 12, 2020.

  1. Clive Jones

    Clive Jones Member

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    Hi guys, I have a Gamo Compact which has started leaking - I.e. I can break it to extend the piston rod but when I compress the action I can hear air leaking out sufficiently that when I immediately pull the trigger, there is no “pop” at all. I have dismantled it down and had the cylinder unit and valve out of the gun and on inspection the valve O-rings all look OK, not torn at all.
    I have ordered and received a valve unit, but it was a different size “nose” and could not be inserted into the valve housing - apparently there have been a few redesigns over the years (my pistol must be 20 years plus old).
    If I put some upward pressure on the base of the valve (the part that gets pulled down to fire the gun)the cylinder seems to hold its pressure when I compress the cylinder rod against the workshop table. Pulling the valve then let’s the air out the breech part of the valve with a satisfying pop.
    With this in mind, it looks like my problem is the nose O ring not seating in it’s housing, only making a good seal when it is pressed home.
    Has anyone else had this problem and what is the cure?
    Thanks in anticipation,
    Clive.
     
  2. Suffolk Sniper

    Suffolk Sniper I’d Rather Be Golfin’

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    Seems we are in the same boat @Clive Jones, I will be stripping mine down again soon to look at the size of the main piston o ring, I know @Blackmax has repaired one of these hopefully he will be along to put his comments up here, I changed all the o rings on the valve but I still had a leak, as you say when the piston was compressed the air could be heard escaping. I was told to pump it to improve the piston seal and to lubricate the piston also to improve the piston seal. Put oil in the little air hole in the cylinder casing. This did work but I will change the o ring as mine is also 20 years old,
     
  3. Clive Jones

    Clive Jones Member

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    Hi Suffolk Sniper, yes, we are in the same boat, a leaky one!
    Although my own Compact seems to be leaking from the breech outlet of the valve block - not the piston seal. I have done the one/two drops of oil down the intake hole on top of the cylinder and this has had no effect on the leak.
    I am now a dab hand at stripping the cylinder out and can do it in less than five minutes. :)
    Please let me know how you get on.
     
  4. Blackmax

    Blackmax Forum Rude Guy

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    Hi guys, I spent hours fixing the one I worked on. I could never get a replacement trigger valve as they were no longer available, I tried O rings of different sizes but could never get the right seal.

    I rebuilt the piston with parts I made on my lathe but there was nothing I could do with the trigger valve due to the unique moulding.

    I bought a second donor rifle but again it had the same fault and I was no further forward.

    Regarding lubricating the piston seals use motorcycle fork fluid, the most viscous.
     
    PhatMan likes this.
  5. Clive Jones

    Clive Jones Member

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    Hi Blackmax
    That is interesting. Did you use random o -rings that you bought/had in workshop or did you buy a Gamo replacement pack (about £8.00 for the four seals) from a supplier.
    The supplier that I bought the valve off suggested I return the valve and purchase a Gamo o-ring replacement kit that they also sell - I obviously do not want to again purchase something if that something does not work..
    Clive.
     
  6. PhatMan

    PhatMan Keyboard Hero

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    Clive,

    +1 on the motorcycle fork oil :)

    I use Fuchs Silkolene 30 weight synthetic.

    Put five (5) drops down the transfer port.

    Open pistol halfway (to cock trigger), close and pull trigger. Repeat ten (10) times.

    Leave pistol overnight, then try a full shot-cycle in the morning.

    You can get to the valve externals by removing the right-hand grip, and then (carefully) the plate that covers the trigger pivots - lube the valve rod from outside (you will see it it sitting vertically).

    Have fun & a good weekend :)

    Best regards

    Russ
     
  7. TrickyDicky

    TrickyDicky Life in the slow lane

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    I just replaced the main piston seal when mine did the same...they go hard with use.
     
  8. Suffolk Sniper

    Suffolk Sniper I’d Rather Be Golfin’

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    Was yours a piston seal attached to the front of the piston or an o ring set up behind the front of the piston, ours are both the older o ring type from 20+ years ago
     
  9. Clive Jones

    Clive Jones Member

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    All good advice, thank you guys.
    I have a small dropper bottle of "gun oil" (the paper that carried the type of oil has long since perished away from the bottle) that I bought from Keens in Aberkenfig many years ago that I used down the cyl intake port and this made no diffence. The leak seems to be from the valve nose o-ring (and 20201113_111520.jpg not the piston seal) as when I depress the cylinder rod of the removed from gun cylinder against the worktop to pressurise the cylinder, the leak is from the breech port of the valve housing.

    The photo shows new valve (the one that does not fit) below current valve.
    Clive.
     
  10. Suffolk Sniper

    Suffolk Sniper I’d Rather Be Golfin’

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    I use Fuchs Silkolene 30 weight synthetic.

    Is this the one @PhatMan ?

    7548DFE3-72A9-498C-A602-D91B6469DA33.jpeg
     
    Blackmax likes this.
  11. PhatMan

    PhatMan Keyboard Hero

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    Suffolk Sniper,

    Yup - thats the stuff :)

    Have fun & a good weekend :)

    Best regards

    Russ
     
    Blackmax likes this.
  12. Suffolk Sniper

    Suffolk Sniper I’d Rather Be Golfin’

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    Ok so I’ve just stripped my Compact down again and these pics show exactly what I am working with

    Firstly the valve which has to my surprise three o rings fitted, I must admit it was only when I saw @Clive Jones valve I noticed the third o ring its green colour between two brass bits on mine, and with the new o ring fitted :facepalm: the full valve unit. I notice that Clive's valve has an o ring above the brass collar where the spring sits mine doesn’t have one here and never has ?

    71A5367A-610F-4B06-B9BB-B85510247DB5.jpeg Original C4D30028-69FA-471B-96F9-48843ED359A9.jpeg Full Valve 3541A1D0-E217-41B7-BC94-BC58785F3479.jpeg New 3rd O Ring Fitted

    Here we have the piston with O Ring seal and a white plastic guide of some kind, this has a cut in it probably to make installation easier

    40C46FA9-81D1-4316-BF68-7E32F9E79E70.jpeg Full Piston. 402A3D90-BF1E-43E5-B623-C2566AA26A3E.jpeg Close up. 849828CD-B8C5-43CD-A873-9C06B89EA15D.jpeg O ring and guide washer


    356F054E-4126-4FB1-B33E-20847DE2B266.jpeg Stripped down piston. CEC493F0-8030-4EB6-9972-2DEB9E4FB074.jpeg O ring and piston details


    I have also replaced the breech seal rubber as well (No pics of that as its so straight forward) And the larger o ring where the piston cylinder meets the valve body.

    There’s not much more to these pistols than this really apart from correct lubrication which hopefully @Blackmax and @PhatMan have sorted out for us.

    I will now try to find a replacement piston seal o ring @Blackmax you mentionEd an NB70 nitrile material is that better / more hard wearing than a general rubber one.
     
  13. TrickyDicky

    TrickyDicky Life in the slow lane

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    Yes seal attached to the front of the piston...thought that was the older type.
     
  14. Clive Jones

    Clive Jones Member

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    Yes, there are two seals either side of the brass spacer. I cannot say that these are original parts as I bought the gun secondhand 15-20 years ago or so but it fired well until a few years ago, so they did work.
    There is also the nose seal and the bottom valve seal.

    On the new non-fitting valve there are the nose, base and one seal between the plastic(?) spacer and the brass valve threaded body. This seals the gap between the valve pushrod and the brass body in my estimation.
     
  15. Suffolk Sniper

    Suffolk Sniper I’d Rather Be Golfin’

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    I bought mine sometime in the mid 90’s cant pinpoint when exactly but as you can see from the pics above an o ring seal
     
  16. Blackmax

    Blackmax Forum Rude Guy

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  17. Blackmax

    Blackmax Forum Rude Guy

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    Sorry Clive, I got a bit confused in my old age. Yes I’ve fixed a number of Gamo compacts successfully, I got my own supply of O rings.

    Initally I thought you were referring to the Gamo MC Super which I never managed to fix due to the unavailability of the trigger valve.

    I used Silkolene on the piston O ring no failures! :thumb:
     
    PhatMan likes this.
  18. Clive Jones

    Clive Jones Member

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    Hi Blackmax,
    That is great news.
    Have you any input on to why I can seal the valve by pressing it home against the seat but if I then release (fire) it and compress the cylinder again without pressing on the valve the air escapes through the breech seal. This is with the cylinder off the gun.
     
  19. Clive Jones

    Clive Jones Member

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    Blackmax, as an addendum to the above, is there any difference in the seals that you have put in the older Gamo Compacts, to the newer ones? We know the actual valve bodies (the metal parts) are different.
    Clive.
     
  20. PhatMan

    PhatMan Keyboard Hero

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    Clive,

    With the cylinder off the pistol, does the valve stem move freely up and down ?

    The valve spring is supposed to hold the valve closed during the cocking cycle, and the hammer then knocks this open when you pull the trigger - so the default position is valve closed.

    If you remove the valve, can you shine a torch in to have a peek at the valve seat ?

    Have fun & a good weekend :)

    Best regards

    Russ
     

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