On Board Air by Dan Dohrn

Airing down your tires is often a requirement of many off-road adventures. Airing down is the easy part, it’s getting the air back in that becomes the challenge. There are a few options out there, such as 12v compressors, a Power Tank, or a York air conditioning compressor run by your engine. A Power Tank holds a limited amount of air and takes up a large amount of space. A 12v compressor is small, but does simply does not live up to the task of providing enough air. That leaves the York. If set up with an auxiliary air tank, the York will provide a very impressive amount of air. Enough to air up your tires in a matter of minutes and run air tools. 

After locating the proper York Compressor to use for my system, I removed the pulley and decided to clean up the compressor and give it a coat of black paint. The cleaning turned out to be a lot of work since there was a thick layer of greasy dirt and lots of little crevasses for it to get down into. The paint didn’t turn out perfect, but since the York is aluminum, there is no chance of rust, so I didn’t worry about it much. 

The next step was to decide how I was going to mount the compressor to my engine. I was originally going to go with one of Brad Kilby’s kits from http://www.onboardair.com/. They appear to be very nicely made kits, but I wanted to save some money  and have the enjoyment of putting together the whole OBA system myself. So off to the junkyard I go. I spent a couple hours wandering around only to find a gazillion mounting brackets for V-8’s. I finally found an Eagle station wagon with a 258 that had some of the brackets and idler pulleys, but not the bracket to mount the York compressor. I figured I was going to have to have a bracket made or spend a lot from a specialty Jeep shop. Finally, I tried a tiny local junkyard that only has Jeep parts(I had tried there before, but they were closed). Sitting in a cardboard box were all the brackets I needed. You need the brackets in the drawing to the left and an additional bracket to relocate the alternator as seen in the picture to the right. The brackets all mounted to the engine without any trouble. The alternator bracket did take a little time to figure out exactly how it went on. Below are pictures of what the brackets look like mounted to the 258 engine:     

New alternator mount	York bracket	Idler pulley & bracket

The next step after mounting the brackets and idler pulley is to mount the York compressor. This was slightly challenging due to the limited amount of space between the York mounting bracket and the alternator. You will need to move the alternator out of the way in order to have access to a couple of the York mounting holes. The next thing to do is measure for the v-belts. I first adjusted the idler pulley bracket and the alternator (the two moveable items to adjust the belts tension) to slightly less than half way to give plenty of room for belt adjustment. I then grabbed a section of rope and wrapped it around the path of the pulleys and measured the rope for belt length. You may need to add an inch or two onto your rope measurements since the rope will sit farther down in the V-belt pulleys than the belt will.  The belts I ended up with were a 17300 (30 inches) for the York to alternator belt, and a 17560 (56 inches) for the belt that went from the York to the idler pulley and then down to the main crankshaft pulley. The belt to the power steering pump and fan can be used same as the stock setup.  Below are pictures of the mounted York and a diagram of the V-belt setup for my 258 after the York install. 

York mounted to 258	Pulley diagram	Another view of York

After the York is mounted to the engine, then you need to plan out and hookup the air lines.  I chose to mount my 2.5 gallon tank from http://www.onboardair.com/ in front of the gas tank under the tub of my Jeep. There is plenty of room for it there and it is out of the way and protected from most things hitting it. For the manifold, I used a 1/4 NPT female pipe cross. I minimized what was under my hood by  putting the relief valve and both the front and rear air lines on the tank. That left me with only a pressure gauge, the pressure switch (Square D part# 9013FHG12J52M1) and an oil/water filter under the hood. For the fittings on the York, I decided to purchase the Rotolock fittings from onboardair.com. I used a PCV breather filter from an import car for my intake filter. It looks like a mini K&N filter.    

Rotolock fittings	Under hood  plumbing	OBA manifold	2.5 gallon tank

I ran the air lines along the frame rail to keep them protected from getting snagged on anything or getting any damage from excessive rubbing. I put a quick disconnect on the front under the driver side fender. For the rear quick disconnect fitting, I got a little more creative. Since H8PVMNT has a YJ tub, there is an unused hole on the driver's side rear of the tub where the fuel filler for the YJ was originally located. I used that hole for mounting my rear quick disconnect and it is protected by the flip down license plate.  To protect the front quick connect from accumulating dirt and mud, I bought some 7/8" furniture feet that you would use on a card table or chairs. They are a snug fit and will keep the connections free of dirt, and best of all they are cheap. 

Air line routing	Front quick connect	Rear quick connect	Rear hidden by plate

Here is a "schematic" of the parts I used for the airline plumbing. It is not to scale, just a representation of the parts I needed for my system. Click for a larger view:

The electrical connections are really quite simple for this. I mounted a lighted switch under my dash and ran one wire to an ignition switched source on the fuse box, one to ground, and the third to the pressure switch. Then you simply wire the pressure switch tot he clutch wire of the York and you are set. The switch is wired to a 12 volt source on the fuse box that is only hot when the key is on, that way the York clutch will not get power while the engine is not running and drain your battery. The pressure switch is pre-set to come on at 95psi and turn off at 125psi. When the engine is running and the dash switch is in the on position, the compressor will automatically turn on and off based on the pressure in the tank. With the switch in the off position, the compressor pulley freely spins and does not pump any air, regardless of the pressure in the system.

I haven't added up the expense of the OBA system yet, but as with all projects it turned out to be more than expected due to a gazillion trips to the hardware store for little bits and pieces I forgot to buy. It was a very rewarding project however and it will see much use in the future.