Friday, December 25, 2009

Daisy 717 Repair Part 3 Final

Wow, only four seals in the old gun and it almost made me bang my head against the wall. The joy of damaged pneumatics.

Daisy got a new 717 barrel/valve assembly to me in only three days. Thanks Daisy! It arrived on Christmas Eve via first class USPS. I considered upgrading to the Lothar Walther barrel of the Model 747 but it was about $33 more dollars compared to the standard 717 barrel priced at only $17. Though, if you think about it, a Lothar Walther barrel for $50 is a good deal. Still, my 717 was broken and the outcome was unknown, so there wasn't much incentive to spend the extra coin.

Old barrel on top. There's a flat on the old barrel near the muzzle. New barrel has no flat yet retrofits just dandy.

A bit concerned when I saw the flakes of material in the leade. Was only some black paint flakes left from the masking. Came right off.

This is the original 717 valve seat. It was made for the early cone-shaped check valve. Daisy still uses this same casting but puts a small beveled edge on the hole. I didn't find any other differences in the valves.

Installed the new assembly and all seemed right in the world. The old stretched casting was indeed allowing the valve to move backward under pressure and leak through the breech slot in the compression tube.

A day later, I heard a tiny hiss as I charged the pistol. A much smaller leak than before but it was there.

I left a comment at the end of Part 2 to Bobby about making some shim washers...

Just cut them with a pair of snips from some thin scrap on the bench.

And installed them in the forward portion of the locater hole. The right side plate (Daisy's part number 717-10) has a protruding stud that fits into this hole. All the compressed air pushes against the stud. Like the original valve, the stud is apparently damaged slightly, too. Forced slightly backwards from an over extended pump assembly.

With the shims packed in the front of the hole, the valve is pushed slightly forward into the compression tube giving the o-ring more support. Talking about a few thousandths here. And that's all it took. Problem solved. I looked hard at the stud and really didn't find any obvious damage but it must be bent backwards ever so slightly. So there it is. I thought the gun had one problem with the check valve and the gun actually had three issues: bad check valve, stretched hole in the valve body and bent locater stud in the right side plate.

The gun chronographed consistently in the 360 fps range with .177 cal RWS Hobby pellets. After leaving the gun charged for 15 minutes, it clocked 362. If I do get another leak, I'll just stack one more shim in the hole. Ideally, the seal on the valve face would sit deeper inside the compression tube by another 0.050" or more. If so, the gun would likely never have developed the leaks that it did--even with the stretched holes in the valve.

I think the gun is a prime candidate for some custom grips. We'll see what happens.

Monday, December 21, 2009

Daisy 717 Repair Part 2

Before I get too far ahead, I installed the new foam wiper seal and a size #115 o-ring piston seal. Got 'em from Daisy a few weeks ago for a dollar. One whole dollar nets you two o-rings and a foam ring of the correct size. I bought 3 kits just for the novelty of having spares. Screwed the piston head back onto the body and reinstalled it into the compression tube. Coated all the mating surfaces with moly... and bolted it back together. Back to the valve. Popped off the snap ring The exploded valve. Original seals are on top. Replacements scavenged from various o-ring kits are below. The o-ring on the left for the body of the valve is a #012 And the small stem seal is a #005. Reassembled. Put it all back together and it still leaked. Super. Just for kicks, I then installed the new style valve. As I expected, it leaked. The pump assembly does not need to be disassembled to get the valve out of the 7XX guns. Just the three phillips head screws on the left side of the shroud need to be removed. Pull the grip frame off and it all comes apart. I can get the valve out now in under 60 seconds--blindfolded. Then I took the valve apart. Again. Sure, no problem I'll just clean up the valve stem seal on the lathe. Matched the angle and literally just dusted the surface with the cut. Reassembled. With teflon tape this time, too--just for good measure. Yep. Leaked. Not to be outdone, I'll just add an o-ring to seal the valve... Cut the stem seal down to fit a R-01 o-ring. And gorilla glued it in place. Like so. Reinstalled--Reassembled--Leaked. It slowly occurred to me that it maybe wasn't leaking from the valve after all. I held the barrel assembly in the compression tube with a tight fitting drift and cocked the gun. It held. Moved the drift slightly and it leaked. The o-ring on the face of the valve is allowing blow-by. Removed the size #115 o-ring. Looks fine--actually it is fine. It's brand new from the one buck Daisy seal kit. Then I saw the problem. If you look carefully at the round hole in the casting you'll notice that it's not actually round. It's oval shaped and allows the valve to sit too far back in the compression tube. Only talking about a couple hundredths here, but it's enough to allow air to leak past the o-ring very slowly. Sounds like it's coming out through the transfer port. But, no, it's leaking from just in front of the transfer port. Thought about shimming it, then just called it quits and called Daisy customer service. A new barrel/valve body assembly cost $17 bucks. Sold! Good news is that the new body will work correctly with the extra valve I have. And, yes, I ordered another check valve as a spare. Will it work? What else could go wrong? This is why I don't work on airguns for a living... Well, it's one reason.... Initially, I thought the gun had somehow been over-pressurized--maybe someone attempted multiple pump strokes to get more power. But Nick hit it on the head. A previous owner over-adjusted the piston stroke and it levered the valve backwards on the closing stroke. Yeah, I need a new part. Note to 7XX owners: The lever should close with just a bit of resistance. The parts are soft. Be careful.