Finding that damn leak! FX Bobcat

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Pauly5

Pauly5

Member
Aug 6, 2015
169
30
Wellington, New Zealand
I feel like i'm asking about a dinosaur in this age of many models since, and I have watched the videos on how to change the valve and seat on the Boss/Bobcat. It's just that I can't seem to find the leak. It's a Mark 2.

I have a new valve and seat, but suspect that maybe the valve and piston seat don't marry up perfectly to get a seal, and so suspect the leak is through the valve. I have pushed the seat into place with a wooden dowl, I have polished the seat by turning it in a drill chuck and polish. The tank doesn't leak, and I have replaced O rings on the reg and pressure gauge also.

Tonight I will remove the shroud and put a balloon on the barrel to see if it is leaking through the valve, and will tape a bit of balloon over the valve spring adjustment screw to check there too. I guess i'm after anyones experiences with fixing or finding leaks on this gun please? It's such an accurate and enjoyable gun to shoot.

Thanks in advance.
 
I would say perform a leak test on spots where the high pressure air has to be contained like pressure gauges, venting holes, air cylinder connections etc . You can use quite some different methods for this like saliva, soap and water, leak tester fluid and probably a lot more to do this. If this isn't the case than probably you have an internal leak like the valve and valveseat combination, don't expect an inflated balloon when you come back if this is the case. The air will leak out next to the valvestem and shroud if that is still on, what you might see is that the balloon bubbled up if you made it flat after attaching it air tight. With bubbled up I mean like the first puff of air into a balloon before the material start to stretch while being inflated
 
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Well we have progress, thanks to the soapy water. Can't believe I didn't remember it. Another thing that was made clear was trying to create a hairless and dustless environment,

So first test with soapy water had air coming out of every hole, Reg breather hole, barrel and valve spring adjuster. found the smallest of hairs in the reg o ring and valve spring adjtr, so fixed that. Then I came accross something very interesting. I found a very fine, hair like filament of metal in the valve seat area. Now it has either come off the old seat, or the body where it seats.



1560337505_17122617735d00dc61bdf6d7.42575941_20190612_212143.jpg


After examining the old valve seat, I noticed it had a quite sharp lip on the face that goes into the body, so it is possible It has either cut it from the body, or broken off the seat. One other thing I noticed was that I might have made a small score mark while trying to hook out the old valve seat, as it was in pretty tight, and I wonder if these small marks are possibly stopping the seat from sitting correctly and therefore causing the valve to leak. I can hold my wet finger over the barrel end and see it bubble. So any tips on how I rectify that? Really hard to photo, but you can see the brighter spots in there, and I don't know if they are proud, or just visual.



1560337630_12894525385d00dcde961135.53096490_20190612_215557.jpg

 
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Cool! A great way to upgrade the stock. Does it wear well? By that I mean if you're using it for pest control work, you end up with scratches and bumps, so does the print stay stuck, or can it peel?



Back to my issue sorry. If I have damaged the main block where the valve seat inserts, especially if it is down the wall where the O ring needs to seal, what could I do? I don't have stunning tools or a lathe. My first thought would be to use a fine wet and dry paper and try and lightly buff/polish out any scratches. Failing that if I had proper tools maybe drill/reem it smooth and make a new valve seat.

Can the main block be bought? It seems you can buy everything, but the main block?

Thanks.
 
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I feel your pain. I did the same thing on one I was working on. Ordered new valve seat and stem and it still leaked. After taking it apart several times I found the small scratch from when I took the original seat out. No more sharp metal tools for that anymore! I ended up polishing it out with very fine wet sandpaper and it has held fine. Just have to be careful and not remove much metal, just polish that scratched area.
 
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I feel your pain. I did the same thing on one I was working on. Ordered new valve seat and stem and it still leaked. After taking it apart several times I found the small scratch from when I took the original seat out. No more sharp metal tools for that anymore! I ended up polishing it out with very fine wet sandpaper and it has held fine. Just have to be careful and not remove much metal, just polish that scratched area.
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Hi Randy, thanks for that. Yea I was getting to feel I had stuffed it up totally, and it sounds very similar to my experience so far. I will try that next, Thanks



Great avatar too! I hope 68 ain't your birth year, or that would start to become too many coincidences?
 
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Cool! A great way to upgrade the stock. Does it wear well? By that I mean if you're using it for pest control work, you end up with scratches and bumps, so does the print stay stuck, or can it peel?



Back to my issue sorry. If I have damaged the main block where the valve seat inserts, especially if it is down the wall where the O ring needs to seal, what could I do? I don't have stunning tools or a lathe. My first thought would be to use a fine wet and dry paper and try and lightly buff/polish out any scratches. Failing that if I had proper tools maybe drill/reem it smooth and make a new valve seat.

Can the main block be bought? It seems you can buy everything, but the main block?

Thanks.
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You can probably buy the block, I bought two blocks for a Boss (very similar) in the last year and iirc was 208$. VERY reasonable. If you need to go that route, is there a reason to think there's a scratch there? Sometimes in taking everything apart inspecting and reassembling will fix the issue. (Something not seated properly, gunk on a sealing surface etc)
 
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You can probably buy the block, I bought two blocks for a Boss (very similar) in the last year and iirc was 208$. VERY reasonable. If you need to go that route, is there a reason to think there's a scratch there? Sometimes in taking everything apart inspecting and reassembling will fix the issue. (Something not seated properly, gunk on a sealing surface etc)
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What currency was that? I have been quoted $320 GBP yesterday. A link would be great. Hopefully I fix the problem before having to buy a new block.
 
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After being faced with the possibilty of doom for my Bobcat, I left it alone and went for a quick hunt with my trusty R3. I bagged a couple of rabbits, and enjoyed a full moon and a calm night.

1560582617_19308862745d0499d9cac6c6.84471784_20190614_175557.jpg


So the next morning I had a real good think. There were only two possibilities for the leak. 1. Around the O ring on the valve seat, or 2. Valve seat and valve stem not aligning properly.

I had now way of knowing. I spent some time gently smoothing the sealing face that the seat, sits on, so that I knew that was flat, and the leak persisted. Next I managed to photo the seat, and I could see what looked like lines in the wall of the seat area. I could also feel these with my dental pick when I ran it along it, si I figured it must be that the O ring can't seal properly. You should be able to pick them up if you zoom in.

1560582944_8351323245d049b20dcc9e6.16432962_20190615_144804.jpg


The next move was to find a small 8 mm washer, and using my drill press I put it in the chuck fastened between two nuts, on a bolt, and used a file to reduce the overall diameter, fortunately the ID was adequate. I was going to use this to pack out the valve seat so hopefully the o rings had smooth wall to seal onto.

1560583139_2105488985d049be3839a68.04480811_20190615_155602.jpg


1560583158_576731375d049bf68b6b30.18685359_20190615_155655.jpg


After cleaning and polishing it, I put it under the valve seat and reinstalled everything. I did not expect it to work, but I can't feel any air pressure from the barrel now, yessss.

Time will tell, and I am hoping the morning will present me with stationary pressure gauge.
 
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