The only oil I use in my air tools is a bottle of "air tool oil" that I suspect I got from Harbor Freight. That is about gone so I probably need to upgrade anyway. I have heard that ATF is a good substitute and I have some in the shop, any thoughts on that?
Air tool oil is single use. It goes in and gets blown out. So you want something that doesn't smell (so no to ATF), and don't need anything especially good (there's no need for additives, etc.). MMO is a good solvent at breaking down varnishy gunk, and I've had great luck with their air tool oil, but HF air tool oil is fine too.
However, for a stuck tool, you want an extra thin penetrating oil. Spray that in and give it some air to circulate the oil, and then give it a chance to loosen any gummed up oil, and you may just get it moving. Then with the air disconnected, put on a socket and turn it a few times to move the rotor around. More penetrating oil, more air, more turning and maybe let it sit overnight. Try this before disassembly.
As for disassembly, these are almost all the same. There's usually four LONG screws that hold the back cap onto the hammer casing, just like how the end bells are bolted onto an induction motor. Take these off, wiggle off the back cap (paying attention to the orientation of the cap and any gaskets between it and the air motor housing, and the rotor usually comes straight out the back. Clean out and oil the vane pockets and vanes, and reassemble.
The other possibility is something failed in the trigger valve. Usually it's an o-ring or a seal.
First drop about 5 drops of Marvel Mystery oil into the inlet, then attach it to air and spin it up. The vanes become gummed up from sitting around or using the wrong oils to lubricate it. If that is the issue you will hear it ramp up in speed. Unless the vanes are worn clean out and the bearings are dry, not much to drag one down. I worked on a few at my job. I only use MMM to lube mine. It also comes in a small squirt container. No need to buy large volumes.
Yep. As for wearing out the vanes, I'll bet just about anything that's not the case. I know someone who professionally did tire changes for some years who wore out numerous sockets, and when I disassembled the impact that did it all, the micrometer confirmed no measurable vane wear. I was planning on fully rebuilding it, but a good cleaning was all that was needed.
