Rebuilt my compressor today. I picked up a rebuild kit from X8R on eBay as it was the only full kit I could find. Its crap. Even though I bought the most expensive kit to be sure I had all the parts, the kit is missing numerous o-rings. Certainly NOT a rebuild kit by any stretch. Part of the problem is I have not located a full guide on how to rebuild a Hitachi compressor. Had I, maybe I could have seen how many o-rings are really needed. Lots! However, I still consider the job a success less one issue.

I had planned on lots of photos and such, but when I came across the missing o-rings, I just wanted to get it done knowing I could not show it all.

Remove the drier first. Its plastic and fragile. Remove one screw and turn to line up a small tab, it then slides off with a bit of force.

What I did was thus a partial rebuild. I replaced the main piston rod bearing. It was actually in decent shape but showed signs it would not last too much longer. It was a little stiff but smooth. And some black grease was working its way out from behind the rubber seal. A new bearing is 627-2RS. I think 627 is the bearing with -2RS meaning two rubber seals (sealed on both sides). While its in a sealed environment, I recommend getting the sealed bearing. 7mm bore with a 22mm outside diameter and 7mm width. Similar to a skateboard bearing, but those have an 8mm bore. eBay can be your source for a new bearing. They are very inexpensive. To replace I used a series of sockets that just fit to act like stands as I taped out the old and pressed in the new. Some silicone spray helped with installing the new one.

The piston head was rebuilt. Doing so was not obvious at first. There are two replacement parts. A sidewall sleeve and the piston ring. The sleeve is easy and self-explanatory. The piston ring is not obvious. Basically you cut the old one off. Then you very, very carefully pry off the retaining ring. I left some old ring in place to help protect the aluminum. With the ring off, the new piston ring going in place and you simply tap the retaining ring back down. Do so until the piston ring no long spins around. You want it tight. The only thing I did not replace was the piston to connecting rod bearing (inside the piston). I did not have the part. There was some slight play. A small portion of grease or oil should maybe be applied in there. The piston fits MUCH better into the cylinder. I applied some silicone spray lube to help with break-in. Never use a petroleum lubricant as it can damage the nylon.

The cylinder, where the piston slides, it easy to remove. Use some penetrating oil on the four long screws. Be careful with the reed valve (flat metal piece. Not its position and placement. But it is keyed to the cycler head. At the bottom of the cylinder is a gasket. Clean off the old and install the new one. If you dont have one, use sealant. If you do have the gasket, coat with sealant anyway on both sides. The top of the cylinder has a single o-ring.

The intake/exhaust manifold. I move the exhaust solenoid (blue/white wires). The kit was missing o-rings for this part. There are two, a larger orange one and a smaller one. I cleaned them before putting the solenoid back in. I noticed there was a lot of black debris in there. I cleaned everything out as best I could. NOTE - there is a VERY small white filter at the center where the solenoid tip goes. I removed and cleaned mine.

The drier is easy to rebuild. Mark the exterior in some way that the cap can be installed corrected before removal. I did not have a drill on hand to dismantle the main filter set, so I used my Dremel to cut the factory rivet via grinding. I found the screw in the kit it WAY too short. I used a rivet to sandwich the filter parts together. Not a big deal I guess. You may need a longer screw.

The connecting rod cover does not use an o-ring although it was designed for one. A good amount of sealant it fine. Apply sealant and put the cover on but do not tighten. Let the sealant cure for a while, then a final tighten. That will let the sealant act a bit like a gasket under compression.

I guess thats a little bit of info. Added some pics. Maybe someday, if I do this again, I will make a more detailed step-by-step guide.

 

All these years later, and this statement is still correct. There are no less than 10 rebuild "kits" available from eBay and Amazon, but none of them are complete. In fact, most of the kits have bleed over, so if you end up buying 2-3 kits to get everything you'll need, there will be some duplicity. The most frustrating thing is that none of the kits I saw included an itemization of what exactly was included, just several photos of parts and then some parts diagrams with maybe some arrows. This process was annoying. To save some time for folks, here is what I ended up going with:

JPO500010 - This one has two o-rings (I think for the drier), two springs (not sure what for), and two valves (one for delivery air, the other for exhaust)
LRNJLR023964CYLINDER - This is a new compressor cylinder
X8R27 - This is a piston rebuild kit, which includes new seals and o-rings for the piston and I believe the cylinder head
627-2RS - Bearing which Dakota specified
Bulk Orange Silica Gel (2 lbs for $17) -- supposedly the orange stuff is non-toxic, it's the blue stuff that is carcinogenic. I already rebuilt my drier, so I plan to just clean out the filters and replace the beads.

The only thing I wish I could have ordered but didn't see was a new reed valve. I'll see about an update when I've rebuilt the compressor next weekend.

 

I think 4x4airseals.com has the best solution. Good rebuild videos as well. You will pay a little more and shipping is more but their product is quality and comprehensive.

 

I've used a couple of their kits and going to order another for my spare compressor, might get the alloy end cap as well even though its a bit pricey.
I have my original hitachi a spare and a spare cap, swapped my rebuilt one in but found the cap to be leaking at the fittings. Tried the others and they also leaked even though there isnt any cracks in the cap.
Managed to replace the orings in the push fittings and so far so good..

 

I've had my metal cap for 50k miles now . . . zero problems

 

I'd never had problems until now, even other peoples that i have rebuilt there was no issue with the caps.

 

I switched to an alloy cap a year ago, but the PO at one point epoxied the venerable crack from the inside of the cap and it seemed to be fine.

I’ve since run into trouble with my rebuild and just bought an OEM hitachi compressor. I do plan to swap my alloy cap onto the OEM one.