Benji Trail clunk issue
I can't really shoot where I'm at right now and wont be able to put a chrony in front of it until this weekend probably. This is embarrassing but.. I just took it apart recently to apply air venturi metal lube to it and got it back together. I took everything apart to learn how it works. I just took it outside to fire at the ground to see if it's operational (with a pellet, not dry fire) and it's making a metallic clunk sound like the "spring" is shoving one piece of metal solidly into another piece of metal. It did shoot the pellet... It doesn't at all have the massive twang recoil that it normally has either. Any ideas as to what's going on? I'm assuming that I will need to order seals for it too since upon initial inspection the piston seal had some small gashes basically all around it.
It depends if your Trail is a nitro piston or metal spring powerplant. If gas pistoned, it sounds like the gas spring was installed with the rod not being seated in the piston properly and is slightly off-center. If metal springed, you may have a broken spring at the rear spring guide or inside the piston. Both will make that clunk sound when firing. If you could provide the model #, I can advise you on the course of correcting your problem and help with installing the new piston seal.
I'm at work at the moment but it's a gas "spring", not the coil spring. It's a Trail NP2, I will get you the model number when I get home. I will look into ordering new seals today while at work. I couldn't believe the gashes in it, then I felt the edges inside the chamber and immediately realized why people debur in there, it's sharp and jagged!
When I get back I'll take it apart again and try reseating the gas spring into the piston carefully per your first suggestion... I didn't make any effort to properly seat it into the piston, I just slid it right on in once I applied that moly to everything. I put the gas part into the piston with the "spring rod" side towards the rear. One other thing to note is that unlike other guns I've seen, the "rear retention" piece is curved and plastic on the outside, making it very hard to work with a normal spring compressor... I'm kicking myself in the butt for not getting it in front of the choro before I took everything apart!
OH MY! The gas body goes to the rear with the rod seated in the piston. Ahh, no wonder! It was installed backwards. Take it back apart and keep me posted. I hope you can get the gas body removed from the piston. You may have to take a heat gun to separate it from the inside the piston diameter if it got pressed in too deep. I'm surprised that you got it compressed back into the tube like that.
Re-post on your progress!
JB- You're wrong! In the NP2 series, the NP body goes into the piston!!
Check the EVP
I'm pretty sure that the problem is the gashed piston seal, but make sure that you've got everything in the right place.
It's good to see that the "tube plug" and "tube cap" are suppose to come apart! Looks like I'll be ordering a replacement tube cap. It wasn't easy compressing with that thing on there, I ended up cracking it in several places and eventually had to ghettofi my compressor. There is a metal "slot" type situation on the "plug" that you can see in the diagram that fits the end of the spring rod like a guide to hold in place, so that's why I put it in the way I did. I'm now thinking the noise is a combination of my application of the moly and the gashes in the seal at this point but it's just speculation based off of what you guys have pointed out to me and my own logic. I haven't had a chance to take it apart yet, luckily it's Friday.
Ok just an update... Work continues with the gun but I think the noise has worked itself out. Chronied today with Air arms pellets 18gr I think, 690, 692, 699,700, 703, 704, 702, 699, and with the light (13gr I think) JSB RS got 761, 755, 753, 746, and 748 which seems slow to me.