So most accumulators I've seen use a tire valve/shrader thread which happens to be 0.303 - 32 outside thread, lots of accumulators and the shocks on a couple of my bikes too, just another accumulator. Well, John Deere in the big grand FU says we're doing things differently, because we can! Okay, so its a schrader type fitting down in the bottom of a hole! Big hole and deep! It turns out the thread on the ID of the hole is 1/2-20, simple enough, and its pretty deep, and there's an o-ring and bore reduction right as you get to the bottom. One thing I have never tried is cutting threads on the lathe using a tool other than a tap or die, good old fashioned single point threading. I needed a piece of good stock, so I found a big 8.8 bolt, maybe a 16mm oddball, harder metal turns better, smaller grain size. My threading tool wasn't perfect, carbide tipped bit but cheap china construction, very thin carbide. I spun the bolt down to a piece of bar stock with a .502 diameter, a little more than is needed for 1/2 inch fine thread (.480 ish) I cut the small end first, whittling it down to .308 and then threading, carefully removing more until the fitting almost threaded on, a little sanding of the major diameter made a really good fit fit with a bit of drag all the way on. Spun the part around and cut the 1/2 inch threads the same way, testing with the part once it was close for a snug fit, then spinning off the last few threads to match up with the o-ring at the bottom. I decided to add a hex, so bored out a 7/16 nut and pressed it over the adapter, welding it in place and cutting an o-ring groove on the other side to match up with the top of the accumulator. To utilize the remote valve feature, I bored a 5/32 hole down the middle, and stepped it out to 7/32 at the bottom. I took an 8 penny nail and trimmed it to length by assembling the adapter and letting the nail sit on the valve below to find the length. I welded a little bead near the bottom and turned the bead around to just let it slide past the 7/32 bore, then put some stake marks around the bore to lock it in place. This should work just dandy!!
Looks good. Nice to have lathe and mill around to make them special tools.
and it all works well, holds pressure so far, new o-rings end to end better than buying a new accumulator for $1k Might give it a shot at charging this weekend.
Charging was a success, we were unable to get a high pressure regulator so opted for a differential route, namely bleed the line, attach to accumulator, open the little valve and then crack the valve on the nitrogen tank and watch the gauge. I had the accumulator chained and clamped to the bench just in case. On the first one the plastic capplug covering the intake port shot across the shop with a cork gun pop as the piston slid upwards toward the fluid end. Pressure was built slowly as to not slam the piston around, then a nice steady climb to 600, book calls for 500 but figure more gas won't leak into the area. Honed both accumulators with a three stone hone for 5 minutes to remove minor scratches, then buffed with a scotch pad wrapped around the hone for another 20 minutes until everything looked smooth. After charging there were no leaks found, and on reinstall there's maybe 10 shots on each brake pedal after the motor quits, verified on a hill. Now that we have the adapter, it'll be easy to keep everything topped up nice and full.