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Old 02-07-2015, 11:24 PM   #1 (permalink)
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My Misc Metadyne Thumper Meanderings....

Edit* Changed the title of the thread, going to keep all my Thumper stuff here, not just the original question.

Howdy!

So I'm wondering how difficult it should be to move the piston forward and back? I have a thumper with what I believe is the latest piston and it is incredibly difficult to move it. The spring can barely move the piston forward when it is pushed back.

Does this not matter when the marker is aired up or should I be trying to smooth that movement?

Last edited by RuleOfSines; 02-13-2015 at 10:30 PM.
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Old 02-09-2015, 11:16 AM   #2 (permalink)
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Got it! It moves now.
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Old 02-09-2015, 02:04 PM   #3 (permalink)
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You sir, are a glutton for punishment.

You might post up your findings for the other lonely Thumper owners.
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Old 02-09-2015, 02:17 PM   #4 (permalink)
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Quote:
Originally Posted by Spider! View Post
You sir, are a glutton for punishment.

You might post up your findings for the other lonely Thumper owners.
I love strange and finicky mechanical devices

This just turned out to be what I think is an oversized o-ring locking the main valve into place. I have to order a bunch of O-rings to continue experimenting with, since nothing else I have shares the oring sizes in this guy.
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Old 02-13-2015, 10:27 PM   #5 (permalink)
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Sooooooo...

Does anyone know if the front of the bolt/main valve/piston is supposed to actually seal inside the breech, or just up against it?

When the piston extends all the way and into the breech, the forward small o-ring enters the front air chamber, and is promptly torn to ribbons when the piston retracts. This does not strike me as the intended functionality.

Also, I believe it causes me a huge delay on firing, the firing sequence is 3-4 seconds behind the trigger pull. I think its because the piston is bound up on all the o-rings.
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Old 02-15-2015, 04:13 PM   #6 (permalink)
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If anyone can tell me if their working Thumper looks more like #1 or #2, it would be greatly helpful. This will determine some of my o-ring choices.

#1 - Piston extends full into the front cap:


#2 - Piston seals up against the cap, barely entering:
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Old 02-15-2015, 04:27 PM   #7 (permalink)
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#1 looks more like it...
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Old 02-15-2015, 04:31 PM   #8 (permalink)
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It should site flush out to the end more like #1. It appears that #2 has concentric issues where piston is binding. You could try thinner wall orings.
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Old 02-15-2015, 04:33 PM   #9 (permalink)
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Big thanks to you both
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Old 02-16-2015, 11:37 AM   #10 (permalink)
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So I plan on experimenting with PTFE O-rings, curious if anyone has input on that. The movement of the parts in this marker seems to be very poor, combined with the inability to oil it due to the valve.

I'm planning on following the existing o-ring sizes, they seem to be a bit overly snug, but I don't have much better to go on. The o-ring grooves vary in depth by about .02", which doesn't help especially much. I don't understand why they are so wide, either. Particularly the large piston, it seems to move a bit before the o-rings even begin to move.
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