I picked up a VM-68 off eBay about a month ago and it was one of those auctions where the seller says that it "worked last time I used it" but is still being sold as is because they couldn't test it. Well when I got the VM it would not hold air and was leaking out of more places then I could imagine. So I took it apart. Finding out that the spring is behind the bolt not the hammer was an interesting experience as it sent my back bottle ASA FLYING across the room (should have uncocked the gun first). Anyway I found all the o-rings that looked dry rotted or chipped and took them to Home Depot to find some replacements. I now have a pretty good collection of o-rings lol. So after replacing all of the bad seals and REALLY lubing everything up before I put it back in the marker would hold air and was only leaking from the two fittings. No problem bust out a wrench and some Teflon tape will fix that. After the fittings were resealed it was holding air and cycling. I put some more oil in the ASA and dry fired it about 50 times just for good measure and too get some oil in the valve which I didn't want to take apart.
So I then took the VM and some of my left over paint from my weekend trip to Skirmish out into the backyard. I was painfully obvious that the VM was shooting WAY under chrono speeds.
Back to Fixing:
I poked around a little on VM-68.com (this site was a huge help). And figured out that there were two ways to adjust the velocity. First the screw in the bolt and then rotating the "clock" on the valve. I decided since it was shooting really slowly I would check both. First I take the bolt out to find that the asshat who owned this thing before me lost the ball bearings. So as a temporary fix I just opened it all the way up. In the future so I can make finer velocity adjustments would it work to just put some Teflon tape on the threads to keep the screw from moving more in or out when the marker cycles? Anyway onto the valve. Luckily the guy who had this before me did have a valve tool to this was pretty painless. Just remove the hammer/bolt assembly stick the valve tool down there screw in. And this is where I hit my problem I know there are 4 settings which are referred to as 3 6 9 and 12 (like on a clock) but I have no idea what "time" the valve is at now. So I figure the old trial and error method should work out pretty well. I rotate the valve one time to the right (clockwise) and put everything back together. One thing the previous owner did was put thumb screws on all the hardware so all of this assembly/disassembly was pretty painless.
More Field Testing:
So I got lucky with the valve adjustments because the marker was now shooting at least at chrono speeds and will just need to be adjusted slightly at the bolt. This thing is really accurate and I like the heft that it has. It is also hands down the loudest marker I have ever shot. Just the cycling of the hammer/bolt assembly makes this loud CA-CHINK! And my unported barrel is loud too. I love it. Running it with a stock it feels nice and solid and the "recoil" is not so bad. I was surprised how accurate it is. I am going to love using this thing at Castle. That was my hopes to get it running in time for that game. Now that I fixed it I will probably not have to touch it for another couple years aside from basic maintenance. That is my little project VM story I know this is not much compared to you guys but I have never really fixed any old markers before so this was a lot of fun for me. Too bad I will be on the other side of the wall come time for Castle. See you guys there!
Any thoughts on Teflon taping the threads of the bolt to help my adjustments from rattling out of place? I guess either that or trying to find the ball bearing.