Just to let you folks know how detailed Jason was in fixing my DAR .177, here are the notes he sent me.
I couldn't figure out how to attach the .txt file, so here it is in this post...
DAR gen 2 in .177 November 2023
Kerry (backstop)
Things you should know
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1. The small grub screws on the rifle have oversized hex recesses that will slip when a 1.5mm wrench is used. Any time you need to turn one, try first to use a 1/16" wrench. The extra 3 thousandths make all the difference.
I replaced the grub screws in the barrel band so those should turn fine with a 1.5mm wrench.
2. The pivot pin for the cocking arm is prone to backing out. I cleaned the threads and applied threadlocker but it may still want to back out over time. Consider positioning the rear scope ring over it so it can't back out.
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SUMMARY OF WORK
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Replaced all seals in the pressure tube/regulator/valve tube assembly. List of O-ring sizes at the end of this document.
Valve
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Valve seat and poppet rim looked at little sketchy. Lightly lapped them together for good measure.
Noticed poppet's spring seat had slight gouge from the untreated end of the valve spring. Flattened and polished ends of valve spring, and deburred the ID to prevent wear to the seat.
Valve spring cap had self-adjusted very deep (~0.30") into the valve body. This behavior has the potential to damage the poppet if the hammer drives it into the cap. On reassembly, applied threadlocker and set it about 2 turns sub-flush.
Regulator
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Flattened and polished the plastic seal out to 7000 grit.
Polished the valve seat (conical orifice) to improve longevity of the plastic seal.
Used Viton O-rings on the adjuster and the HP end of the piston, for resistance to high-temperature degradation of the refill cycle.
Polished edges of Belleville washers. Stack is a 2P 6S )) (()) (()) ((
Adjusted pressure for requested velocity range of 750-850fps with 10.3gr pellets.
Resulted in brass adjuster standing ~0.005" proud.
Yielded 820fps (15.4fpe) once the hammer spring tension was adjusted to the velocity knee. (Plateau ~850fps 16.5fpe)
First shot after gun has been idle for 24 hours is within 5-10fps of subsequent shots. Good sign the regulator is settled and stable, and ready for an impromptu pesting/hunting shot.
State of tune
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OEM hammer spring was too long. Gun was up on the velocity plateau (read: unnessarily loud and wasting air) with the hammer spring adjuster set to its minimum (flush to the receiver). Replaced hammer spring with a short stiff spring and adjusted the tension to the velocity knee (10.3gr @ 820fps for 15.4fpe).
original hammer spring: 0.046" wire, 0.428" OD, 1.86" long, 10 coils
replacement: 0.062" wire, 0.477" OD, 1.27" long, 7 coils
Muzzle report is noticeably quieter and the shot cycle is more pleasant, and of course will yield a higher shot count.
Shroud
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Drilled and tapped barrel band for a third grub screw. Slightly blunted the ends of the grub screws and polished them to prevent gouging the tube cap.
Applied tape to the muzzle stub and the muzzle spacer to better center the barrel within the shrould. Owner had already applied tape to the baffles to center them.
When locating the barrel band, used a mechanically centered scope to align the barrel with the scope rail. Placed a paint marking across the barrel band for reference.
Other
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Drain screw had slow leak. Felt like it would require excessive torgue to seat the steel ball hard enough to seal 100%. Installed a -003 Viton O-ring into recess so it will seal with grub screw installed finger tight. I left the steel ball in place.
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O-rings
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reg OD 2ea M2 x 14
reg piston (top) M1.5 x 9 (used -011)
reg piston (btm) M1.5 x 3 (used -006 Viton with ID abraded to a little over 3mm)
reg adjuster M1.5 x 4 (used -007 Viton)
reg->tube adapter 2ea M2.5 x 21 (used -117 on gen1)
tube caps 2ea M2.5 x 21
gauge M2 x 10 (used -012)
tube assy to receiver M1.5 x 17 (used -015 70 durometer [1])
fill port (screw) M1.5 x 3 (used -006 90 durometer)
drain screw -003 note: kept the steel ball
[1] OEM metric size produces a loose fit of the air tube assembly to the receiver. The -015 size makes a better fit, but they are stretched a bit more than I would like. These O-rings are not continuously pressurized (only see pressure for a few milliseconds each time the gun is fired) so I think it will be fine...and has been fine for years on one of my guns. But in the event one were to fail, consider replacing it with a -016 or the OEM metric size listed above.
