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PostPosted: Mon Mar 14, 2016 8:11 pm 
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There's actually a few of them...

Worst of the lot seems to be the square valve stem. I've run into this with older guns- a 13-89, a phase 2 13-22, a 66 power master, and an early brown grips 13-77.

Basically, it's a valve with it's stem machined square, while the hole in the valve body remains round. I haven't been able to get one of these to break 300 fps. The only remedy I could come up with was valve replacement. It's pretty obvious one of these is in the gun by the amount of air blasting out through the trigger opening.

Restrictor plate washer~ most often seen in .177 pumpers in conjunction with other detune methods. This is a tiny holed washer placed under the rubber transfer port seal. This one is the easiest to deal with- I just remove and discard it. I either replace the rubber t/p seal, or just give it an oil soak, depending on how badly compressed it is.

Undersized transfer port sleeve. Just ran across this once, in a 13-89 carbine that had a phase 2 hammer system. Some of our cooler headed and handed machinist types here are capable of drilling them out. I don't fit into that category: burn/break drill bits and break transfer port sleeve etc. :lol: For me, the cure is a simple part replacement.

Bleed vent hole. This is the one that everyone is familiar with. I've come across 2 of them (both 13-77's) where the vent was cut too close to the valve stem hole to be plugged with normal methods. I ended up cracking the stem holes on both. Solutions range from epoxy putty's and adhesives to drill and tap to 4 X 40 tpi. I've had some luck myself with radio/tv wire solder (60/40) in- aluminum valves of all things. Not that much heat is required- a bic lighter is enough, provided the hole is properly fluxed first. The bottom of the vent hole will have to be blocked to prevent the valve innards from filling with solder. I use the head of a flat head stainless steel screw.

Last one I'm not sure if it was a factory de-tune method, or out right factory error. Air Master 77 with a far too short interlock lever (bolt lock) The gun already had the restrictor plate under the transfer port seal, and a bleed vent hole to boot. Anything over 5 pumps, and the bolt opens 1/8" on the firing cycle. The gun did this from new in the box. I'm leaning towards a factory foul-up here, rather than a detune method. Just wondering if anyone else has seen similar...

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Doc Sharptail

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PostPosted: Tue Mar 15, 2016 12:04 am 
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Doc Sharptail wrote:
Worst of the lot seems to be the square valve stem. I've run into this with older guns- a 13-89, a phase 2 13-22, a 66 power master, and an early brown grips 13-77.

Basically, it's a valve with it's stem machined square, while the hole in the valve body remains round. I haven't been able to get one of these to break 300 fps. The only remedy I could come up with was valve replacement. It's pretty obvious one of these is in the gun by the amount of air blasting out through the trigger opening.


No you don't need to replace the valve only the valve stem.... :wink:

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PostPosted: Tue Mar 15, 2016 6:23 pm 
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Find a replacement that's big enough for that hole, and sure, I will.
Nothing crosman makes is a diameter large enough...

photos in a bit...

Regards,

Doc Sharptail

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PostPosted: Tue Mar 15, 2016 6:37 pm 
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now you got me thinking Doc
I did one last year and now that you mention the stem size, I cant remember if I just replaced the valve stem
or I filled in the slots with JB weld, :?

edit: I think I remember now :oops:
I just removed the back halve of the valve, and used a regular back half with a new stem.... 8)

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PostPosted: Tue Mar 15, 2016 6:51 pm 
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Would suggest to sleeve it and use an off the shelf replacement stem...or make a stem to suit.

Al


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PostPosted: Tue Mar 15, 2016 7:43 pm 
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That's a bit of work to sleeve a hole like that. I would attempt it if I had access to a lathe. Fortunately I have a bit of a parts stash here where I can simply switch out valve ends...

Regards,

Doc Sharptail

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PostPosted: Tue Mar 15, 2016 9:30 pm 
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Actually pretty easy...with a lathe of course. :wink:

Could be done with a drill press and some ingenuity too....albeit perhaps not to the exact same standard, but certainly workable.

Al


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