I'm rebuilding my crosman 766 again...

[Tack Driver 10]

I thread the plastic bolt with a 8-32 thread then center drill and tap
a piece of 3/16" brass rod. So they screw on and can be changed out.
I cut the "door" off as it serves no purpose for me.

The MRod valve stem will help dump more air.
Since it's made of Delrin and fairly hard it releases very quickly.
A stock 2100 spring should dump 10 pumps.

[bustachip]

Nice, are those probes with the 0-ring on the end for a .22cal barrel?
I'll try the threaded deal.....

TMurray

[Tack Driver 10]

Nice, are those probes with the 0-ring on the end for a .22cal barrel?
I'll try the threaded deal.....

TMurray

The probes in the top picture are 17 cal and the lower picture shows the 22 cal probe.
They all work really well.

[Tack Driver 10]

Here's the hot setup.

Modified the bolt assembly and added a brass adapter so valve caps can be used.
Used a grenade in this example.

As can be seen here:
https://www.gatewaytoairguns.org/GTA/index.php?topic=144083.0

[bustachip]

"Here's the hot setup".
Modified the bolt assembly and added a brass adapter so valve caps can be used.
Used a grenade in this example.



You have some excellent mods, man. Where did you buy the valve caps....wally world...LOL?
Thanks for sharing...

Question on the o-ringed probe, are you using "just" the o-ring probe to seal the barrel, or a combination of
the o-ring behind the barrel with the barrel shortened. I'm thinking these are two different set-ups?

I also tried the white delrin valve stem yesterday, but it didn't seal, so I'll have to look more closely at this.
I wasn't using the factory spring so maybe there wasn't enough spring pressure, and or, completely nick
free surfaces....donno.

TMurray 

[Tack Driver 10]

Most of the valve caps can be found on EBay.
Lots of options or make your own bolt.

Just one o-ring either on the probe or sandwiched between the barrel and breech.
I use the seal on the probe exclusively now.

Does your white Delrin valve stem look like the one below?
They are fairly soft and usually seal without a problem.
If the seat is good you can try spinning the stem in a drill or lathe installed in the back
part of the valve.

If I have trouble getting a stem to seal I cut a new seat using a stubby cobalt 135 degree drill bit.
Press a new Delrin head on the stem and turn the same angle on the lathe.
Cut the outside diameter of the stem head no more than .050" larger than the throat.

[cobalt327]

Good point about using a 135 deg. bit, a steeper angle like from a 118 deg. bit will not flow as well until the poppet is further off the seat where a shallower seat angle begins meaningful flow sooner.

[Tack Driver 10]

Good point about using a 135 deg. bit, a steeper angle like from a 118 deg. bit will not flow as well until the poppet is further off the seat where a shallower seat angle begins meaningful flow sooner.

Right, and use a new 3/8" bit that is only used to cut valve seats.

Cut this seat back some.

[bustachip]

Most of the valve caps can be found on EBay.
Lots of options or make your own bolt.

Just one o-ring either on the probe or sandwiched between the barrel and breech.
I use the seal on the probe exclusively now.

Does your white Delrin valve stem look like the one below?
They are fairly soft and usually seal without a problem.
If the seat is good you can try spinning the stem in a drill or lathe installed in the back
part of the valve.

If I have trouble getting a stem to seal I cut a new seat using a stubby cobalt 135 degree drill bit.
Press a new Delrin head on the stem and turn the same angle on the lathe.
Cut the outside diameter of the stem head no more than .050" larger than the throat.

Great info Tack Driver, thanks for posting! I was working on it before I saw this latest post...lol. I did think
about re-cutting the seat, but I decided to try and lap it first to see if that would work. I turned a piece of
brass rod to fit in the valve fairly close, to hold it square to the seat. Then I super glued a piece of 2000 grit
paper on the end and chucked it in the lathe, then "lightly" held the valve against it while it was spinning.
BTW, both the seat and the valve stem had imperfections on the surfaces. Next I chucked the valve stem
and "lightly" cleaned the sealing face, then I put the stem in the valve and chucked the stem in the lathe and
held light pressure so the two surfaces would burnish together, and it worked pretty good
here's pic after....
   

Nice clean seat....


Back over the chrony with jsb 7.33's it shot 680 fps, and if I held the bolt closed it shot 724 fps.
 Now it dumps pretty much all the air, compared to before. Next I need to build a probe with the o-ring
(I don't have one that small on hand) or use the o-ring behind the barrel. Next week I have a bolt assembly coming so I'll wait on that. 

I did try a mod to seal the bottom of the barrel (not sure if it's needed..lol). I used some heat shrink tubing
and covered the end of the barrel with the TP hole, after shrinking I cut out the TP hole, then trimmed away
all but a small piece and super glued it to the barrel.
Here's a pic.....

I ended it up cutting it into a circle just big enough to seal the hole against the barrel support, I did have to
polish out the inside of the barrel support, because it was too snug of a fit, but it worked. If you have to remove the barrel more than a couple of times it will come off though.
here's the barrel support after polishing the inside (BTW the rear surface where the barrel butts up against
was really rough) just in case I want to seal it there with a o-ring. But I'll probably try the probe first.
 

I'll see how this valve stem works out before I mess with the valve anymore, I've had it out many times now
 

TMurray

[Tack Driver 10]

Nice work on the valve seat.

Sealing all the leaks in the 766/2100/2200 can be challenging.
Before I got a lathe I used a drill collar to seal the barrel to breech.
With a lathe the seal can be cut captive in brass in a slot and be made smaller.

Also nipping the nose on the valve cap to match the cup helps.

My 2100 got 825 FPS on 10 strokes with 7.9 CPHPs with a cup piston seal.

[Tack Driver 10]

Here's another method to deal with the TP to breech seal.
I did this on a 22 cal Disco tube pumper that got 1034 FPS with 20 strokes.

For the 766 you'd cut off the nipple.
Then drill the TP 1/4" to the center.
A Delrin TP with a 5/16" radius on one end sits up against the barrel.
A press fit will seal it up nicely.
Another alternative would be to counterbore the breech and use square end Delrin.
Either way pinning the valve should be done.

The hot setup would be the one piece breech using a modified 766 V1 breech.

[bustachip]

For the 766 you'd cut off the nipple.
Then drill the TP 1/4" to the center.
A Delrin TP with a 5/16" radius on one end sits up against the barrel.
A press fit will seal it up nicely.
Another alternative would be to counterbore the breech and use square end Delrin.
Either way pinning the valve should be done.

The hot setup would be the one piece breech using a modified 766 V1 breech.

Hey, I'm interested in any of the mods you want to show...lol. I'm not familiar with the 766 V1, my 766
phase II is the only pumper I've ever had apart, I normally shoot HW springers.

I get the idea of your post, however, from the pic is the slotted opening in the barrel not going thru, It looks
like a radius on either side? And the delrin piece still has a small tp hole going thru it, or opened up?

The other end of the delrin is a press fit in the valve?

I think I'm sealed at the valve, the breech end of the barrel is where I'm probably getting blow out.
But at least there are alternatives to seal about everything.....lol....thanks.

TMurray   

[Tack Driver 10]

The slotted opening is the TP in the barrel.
The circle around it is there to show the boundary of the TP.
The Delrin is center drilled to whatever port size is required.

Just wanted to show another option.

[bustachip]

Are you using a #004 o-ring on your probes for the 177cal barrel?
Thanks....
TMurray

[Tack Driver 10]

Are you using a #004 o-ring on your probes for the 177cal barrel?
Thanks....
TMurray

I found a 004 seal is too big and a standard 003 seal is too small.

I used a 003 duro 70 poly seal but cut the gland diameter .100".
Fine tune it with a needle file and test fit.
This stretched the 003 seal slightly and fit perfectly.

There's a metric seal that might work but cost $1 each with a minimum order of 100.

[bustachip]

I found a 004 seal is too big and a standard 003 seal is too small.

I used a 003 duro 70 poly seal but cut the gland diameter .100".
Fine tune it with a needle file and test fit.
This stretched the 003 seal slightly and fit perfectly.

There's a metric seal that might work but cost $1 each with a minimum order of 100.

Thanks, I was looking at the o-ring chart trying to figure out which one would work the best, and the #004
looked pretty close, that's why I was asking.

Is this similar to what your using?
https://www.mcmaster.com/#9558k49/=1dloa20

TMurray

[Tack Driver 10]

Yes, those are the ones but $3 each is very high.

Here's where I get mine @ $.30 each.

https://www.theoringstore.com/index.php?main_page=product_info&cPath=367_1321_1323&products_id=27478&zenid=35e66116da30d2d4492506ca75066884

[bustachip]

Yes, much cheaper...lol, I'll order couple of those and hopefully shipping won't be $10

Thanks again....

TMurray

[Tack Driver 10]

Yes, much cheaper...lol, I'll order couple of those and hopefully shipping won't be $10

Thanks again....

TMurray

Shipping is free if you buy $150+ of goods....LOL

Here's a close up of a 17 cal probe.
Sets the pellet deeper past the TP.

[bustachip]

Shipping is free if you buy $150+ of goods....LOL

Here's a close up of a 17 cal probe.
Sets the pellet deeper past the TP.



Looks Great, I hope to make one similar when I get the new bolt assembly. I did make the little probe ext
about .200" longer on my current bolt assembly to push the pellet in deeper.

I'll pay the $6 shipping on this order...lol, don't need $150 of o-rings , but it's good to know of this
website for future o-rings. McMaster-Carr doesn't  tell you the shipping cost until after the order is placed,
and most of the time it's $15 for a $2 item...lol.

TMurray