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White92 12-26-2007 11:04 AM

On Board Air
I have quite a few air tools and was thinking it would be really nice if I could make my rig into a mobile workstation. Does anyone have on board air in there CJ? How much price wise am looking at?

JeepHammer 12-26-2007 11:14 AM

A lot of guys over think OBA, and miss some of the finer points...

Do you just need one for an occasional trail repair, airing up your tires on the trail, ect.?
Or do you plan to use it for hard core automotive repair?
How big of an air tank(s) do you have room for?
How versatile do you need your system to be?

If you plan to just air up tires, and power the occasional air tool on the trail, the you will probably be fine with one of the larger volume electric compressors.
We're not talking the 'Wally-World' cigarette lighter compressor, but an actual industrial quality DC powered, oil-less compressor...

The good points of electric are, EASY TO INSTALL!
These things are a snap to bolt in and wire up!
No oil in the compressor means no oil crap you will need a filter for!
Larger tank volume will make up for a somewhat smaller displacement of the electric compressor.
Another large advantage is you don't need the engine running to make pressure.
These little compressors are easily portable, so they move from your off roader to your tow vehicle, to your daily driver pretty easily.

If you intend on larger projects, like a 'Repair Vehicle' for a club, or if you feel the need to power things like DA sanders or spray guns, then it's a good idea to use an engine driven compressor.
The advantages of an engine driven compressor are, they come in larger output volumes.
Depending on the compressor you use, you can power a high volume device continuously.

Since these belt driven compressors will need oiling for the pistons and crankshaft, you will need an oil separator if you intend to do anything but manual labor work with it.

Assess your needs, decide how much work you want to do on mounting and maintenance, and go from there.

Secondly, If you have a York A/C compressor, you have a very good start to things!
There were a TON of older AMC vehicles that came from the factory with York A/C Compressors, and they are (arguably) the best way to go if you already have one.

Since York is the ONLY A/C Compressor I know of that has an oil bath crank for lubrication, it's about perfect to convert to an air compressor, and if you have one in place now, or have access to one and all the brackets for you engine, it's a VERY good start.

You can use other types of A/C compressors, but you have to use a 'Pre-Oiler' so the piston and cylinder(s) get lubrication, and then you have to use an oil separator to get the lubrication oil back out of the air stream before it gets to the tank and plugs things up...

A York has a 'Wet' Crankcase, much like your engine, and is self lubricating.
This means you don't have to introduce oil directly into the incoming air stream, so there isn't an excessive amount of oil coming out of the compressor.

If you have a York, and your belts line up already, then by all means use it!

There are larger compressors than the York, designed to supply large volumes of air in the pressures that are usable for hand tools.
These are expensive, you will have to design and build mounts for them, you will have to get pulleys to line up so the belts will run true, and you will have to build the air system from scratch when you use them.

I would only use this type of compressor if it was on a dedicated 'Rescue & Repair' vehicle.
With reasonable storage volume, there simply is no need for something that big on a trail rig.

Electric compressors are a viable alternative for 'Hobby' off roaders....
Since that's what most of us are, it's a VERY good alternative.

Electric compressors can be mounted anywhere, so the valuable belt driven/front of engine space can be used for something else,
Electric Compressors are Very easy to install and wire up,
Electric Compressors are very cost effective,
Electric Compressors are very easy to move from one vehicle to another.
Electric Compressors take very little to no maintenance.
The one thing electric compressors are not is, High Volume, but you can make up for that with storage tank size...

Third, Give some time to thinking out your air supply lines/Air System.
Most guys cobble together a compressor from this, a tank from that, then spend a fortune in brass fittings, water pump switches that belong an AC water pumps instead of DC air compressors, and generally cobble up the install until the 'System' is barely functional.

With just a little bit of forethought and planning, you can come up with a rational, easy to understand and install, and very functional air system...

We'll start with the most misused component of any air system...
The pressure switch!
Most guys use a 'Compressor Switch' that is intended for an AC circuit, and is for a water pump (yes, most AC air compressors use a water pump switch)...

It's much easier and makes for a much cleaner install if you use a DC air pressure switch.
In the first place, it is built to switch DC, what you vehicle produces.
Secondly, it's designed for AIR PRESSURE, and it's not a 'Diaphragm' switch that was designed for water pumps.

A proper air compressor switch will have 'Thresholds', upper and lower limits...
Once it's turned on, it will air up the tank to say, 120 psi, or 135 psi, or 150 psi, depending on the switch.
When the system leaks off a little, or the air in the tank cools down from being compressed, and contracts a little, the pressure will drop some.
A true air pressure switch will allow for that pressure to drop some without turning the compressor on and off all the time...
On when the pressure is below 90 PSI, and off when it reaches 120 PSI.
Or on below 130 PSI and off at 135 PSI, or On at 135 and off at 150 PSI...

The second most common mistake is not enough reserve tank total,
Remember, unlike liquids, air tanks can be linked together just about any old way.
If air will go in the tank, it will come right back out through the same line...
No reason for gravity feeds or any of the other silly stuff you have to do with liquids...
So you can single line link as many tanks as you can get mounted in your vehicle to increase the total reserve!

If you have room for 5 one gallon tanks, then that's 5 gallons of air reserve!
And in case you don't know, 5 gallons is a respectable amount of air reserve on a vehicle.
If you have a 'Portable' or 'Lend' tank, you can easily double that, and reclaim the room if you need it for something else!

Third most common mistake is running rubber air lines like like a crazy person everywere!

There is a 'Hard Plastic' line used for brakes in big trucks.
(neither 'hard' or 'plastic', but you know how common terminology is...)

We call it 'Push Lock' line, and it is a great way to plumb things together.
The line is cheap, so if you pinch one, rub one through, or melt one, it's no big deal.
Push lock fittings are litterally a one hand, 10 second change, and you can reuse them over and over again.

This isn't something 'Experamental', this is the same line and fittings required by D.O.T. for big trucks, so they go BILLIONS of miles every year...
And every reasonable parts store (NAPA and the like) and every big truck parts store will have this stuff on hand everyday.

Fourth most common mistake I see is using a bunch of brass fittings to make a manifold.
Industral grease manifolds are a great way to get a manifold cheap that isn't made of brass 'T's and looks like a kid got in to a box of fittings.

If you are handy with a drill and tap, a simple piece of aluminum is a good way to make a custom manifold to fit your specifications EXACTLY, and look good doing it!
Remember, a drill bit is the cost of ONE brass fitting, and the pipe tap is the cost of ONE brass fitting...
So, for the cost of 2 'T's, you can have a custom manifold with a little work...

Fifth most common thing I see done wrong is underutilization of the air supply.
If you have the air, USE IT!

I use my air with a regulator. Regulator make your air system 20 times more useful and easy to use...
Set the regulator for your tire pressure, hook up the hose with a self locking tire chuck, and walk away.
The regulator will air UP AND DOWN with out you having to 'Babysit' with an air gauge all the time.
Set it for 10 PSI when you get there, and it will air your tires down to 10 PSI.
Set it for 35 PSI when you are done, and it will air your tires back up to highway pressure... All without the $150 'Air Down' tools, or having to babysit each tire with a pressure gauge...

My regulator allows me to blow up air mattresses, float toys, camp chairs, spray paint, ect.

My regulator allows me to pressurize my distributor so I don't drown out when in deep water.

I have it hooked to my transmission, transfer case, and axles now also, so my vital components blow bubbles under water, instead of letting in water and dirt/grit.

Don't forget a removable tank!
I use an under body storage reserve, but I also have a removable tank in the bed of the jeep most times...
You never know when you will want to help some one you may not want to get close too...
Or 'Lend' air to someone.

You can either pack around 100' of large bore hose, or have a removable tank you can drop off and get back later.
Since the tanks are dirt cheap at Wally-World, and you can get them out from under any big truck or trailer in the salvage yards, there really is no excuse NOT to make your air compressor a 'SYSTEM' with 'Lend' capabilities...

Here is a simple air system diagram that may help you figure things out...

I'm sure I missed some things, and I'm sure there will be people disagreeing with one point or another all over the place...
And in their particular situation, they may be correct...

This is just an overview of what has worked for us several times in the past, and on our current vehicles, and is a pretty good guideline of what an 'Average' off road vehicle might need.

No_Bs 12-26-2007 12:14 PM

It is not hard at all. The hardest part of the whole thing is finding the compressor and brackets, mostly the brackets. These will be your major expense most likely. After that, its all just fittings and a tank and such. I got a compressor and brackets for free, so I lucked out. Check out
This is the basic setup. I've found that the cheapest place to find most of the pieces is on lowrider websites, for air suspension. FIttings can be had from for less than $30 total.

CNY 12-26-2007 12:35 PM

You can also use a CO2 tank for tools.

Fjguercio 12-26-2007 05:08 PM

Mr JeepHammer

Very nice write up on the on board air.

Great idea using the regulator press to lower and raise the tire pressure. I will use these ideas.

I have been looking at the York Compressor for several months. Once I get the CJ7 1978 running well, will be adding the compressor. I have the mount it came on my vehicle but not compressor. I was not sure what I had till I saw some more pics of air and mounts. I have a picture of the empty York Bracket if you want to post here. If anyone had the higher volume York I maybe interested if priced right.

Here is some information from the WEB on the YORK COMPRESSOR aticle. Not sure of location because I saved aritcle on my PC.

Most A/C compressors lubricate themselves with the freon that flows through the A/C system. In order to use these compressors for pumping air, you need to have an external oiler feeding oil into the intake hose and a filter to remove the oil from the output hose. Certain York-style compressors (the big, boxy, vertical kind) used an internal oil reservoir for lubrication, which makes them ideal for use as stand-alone air compressors. These compressors were commonly used on AMCs, Fords, and (I hear) Volvos in the '70's and early '80's.

Therold Enterprises makes mounting brackets and alternator pulleys to mount an AMC York onto a current Jeep 4- or 6-cyl engine. The guy I talked to was extremely friendly and knowledgeable about the differences in the various kinds of York compressors. He outlined three major differences in the various types: hose connectors, pulley clearance, and piston stroke length.

Unless you have gobs of vertical hood clearance, you really want to get the AMC-style hose connectors, which run horizontally across the top of the compressor. The Ford-style connectors stick vertically out of the top of the compressors and then bend over to connect with the A/C hoses, which adds about 3" to the total height of the unit. The good news is that these connectors are just screwed into the top of the compressor, and the two connector styles are interchangeable on the same compressor. The bad news is that the screw threads on the connectors are closer together than those on most 3/4" pipe fittings, so it's nearly impossible to find connectors anywhere but on another York compressor. At left is a photo of my Ford-style compressor. The photo shows one Ford-style hose connector and one AMC-style connector so you can see the difference.

Another difference between the AMC and Ford versions is the pulley. The AMC pulley is positioned very close (1/2") to the body of the compressor. The Ford pulley sticks out about two inches away from the body. This might make a difference in your mounting bracket because the belt obviously needs to line up evenly with the pulley on the other end.

The third difference is in the stroke length. There are reportedly three different stroke lengths, ranging from less than 7" to over 10". The longer the stroke, the more air the compressor can pump per minute. This doesn't vary by auto maker, so there are two ways to tell which length you've got:

1. If your compressor still has a metal York (not Motorcraft) ID tag bolted to the front of it, there will be a number on the tag that looks like "F2XXY", where:
XX Stroke length
10 = long
09 = medium
07 = short
Y Discharge Direction
L = left
R = right

2. Take off the clutch and look at the crankshaft.
 Remove the center bolt (1/2" socket)
 Remove the large washer
 Run a 5/8" coarse thread bolt in until it forces the clutch off
 Look at the end of the crankshaft. The end is flat on all models.
 If the edge of the flat end is beveled, you've got the short stroke.
 If it's a sharp corner, but with a thin groove for a retaining clip, you've got the medium stroke.
 If it's a sharp corner without any groove, you've got the long stroke.

I've seen junk yard prices for old Yorks ranging from $12.50 to over $50. I had to pay $30 for my Ford model off a late-70's Fairmont, then shelled out another $20 to get AMC hose connectors and an idler pulley off an AMC Eagle at a different yard. If you can, have the yard personnel remove the compressor for you, since the placement of the mounting bolts makes removing it from the vehicle yourself a real PITA. When getting the hose connectors, try to grab a length of hose along with the weird connector. This will make it easier to connect it to your own custom setup later.

Before you lay down your green, make sure the compressor works. To check whether it pumps air, plug the outlet hose with your thumb and then turn the inner portion of the clutch pulley several full revolutions. If, upon removing your thumb, you can feel the pressure difference, then it passed the test.

Ideally, there should be no oil pumped out the hose, but a simple inline filter will fix that problem if it exists. The second test is whether the electric clutch works. The clutch is what locks the outer portion of the pulley where the belt runs to the inner portion of the pulley that's connected to the crankshaft. To check this, ground the compressor case on your vehicle. Then take the single wire that should be attached to the compressor and touch it to your positive battery terminal. You should hear a click as the clutch engages, and turning the outer portion of the pulley should then force the inner section to turn and pump air. When current is removed, the clutch should disengage, and the outer portion of the pulley should spin freely without moving the inner portion.

In order to hold oil, the compressor must be mounted vertically. The oil check/fill hole on my York is about half way up the left (as you're facing the pulley) side of the compressor. Remove the bolt, then put a 90-degree bend in a section of metal coat hanger. Make sure it's long enough so that the end of the wire touches the bottom of the oil sump. I've seen oil level recommendations ranging from 1" to half way up the dipstick. The type of oil used isn't critical--regular old 10W-30 will work fine. A trigger-type oil squirter can seems to be the best way to add oil when necessary.

Mounting the York to an old Jeep with a 258 ci inline-6 should be pretty easy, since this compressor was available from the factory. Just grab the OEM brackets from another 258 with A/C and you're good to go. Mounting it on any other engine requires fabrication of a custom mounting bracket.
Complete mounting brackets for newer Jeep engines are available for $200+ from Therold Enterprises. If that's too steep for you, they'll sell you just the back plate for the compressor, with slots drilled for adjustable mounting bolts, for $12. If you're the do-it-yourself type, you could also fabricate your own

Fjguercio 12-26-2007 06:52 PM

I believe this is the York Compressor mount. Here is a pic of the 1978 CJ7 258 restore I am working on. The mount is part alternator mount and a flat spot for the York to mount to. Can anyone confirm this.

Happy Holidays.

Fjguercio 12-26-2007 08:04 PM

JeepHammer 12-27-2007 09:51 AM

For the most part, that's true.
Some of the finer points...

1. Mount the York upright when you can.
Laid over, the piston rings have to fight the crankcase oil directly, and that is NEVER a good thing.

2. Always use a 'Whip' for about 18" or 2' coming out of the compressor pressure side.
A 'Whip' is a braided steel line designed for pressure and HIGH TEMP!
You won't believe how hot that compressor head and output line gets until you get up against it once or twice during operation!

3. The BEST place to find a York compressor is under your hood.
If you don't have one, or the brackets for one, then you are going to have to start from scratch.

This would be a VERY GOOD TIME to consider an electric compressor...

4. The BEST place to find a LARGE VOLUME York compressor is in a big truck salvage yard.
Most big trucks have two air conditioners, one in the cab, one in the sleeper box, so they ALL use the very large volume York compressors for the most part.
Stuff like that in a big truck salvage yard is 'Cheap'.
Tell them you need a 'Rebuildable Core' and the price goes down even more, since you aren't looking for a working unit for A/C.

5. The 'AMC' style hose connections are actually passenger car style connections. Any old ford car should have them, along with a lot of big trucks.
The hose connections/heads are normally interchangeable, so even if your compressor didn't come with the correct head/hose connectors, you can swap the car style on pretty easily.

The crank case is sealed so it doesn't let the freon out when you are using it for a A/C compressor, but you need to vent the case if you are going to use it for a OBA so it doesn't force oil into your air lines...
With pressure always trying to get past the rings, it will help control the oil flow into the cylinder.
If the crank case is pressurized at line pressure, every time the piston goes down, it will suck some amount of oil into the cylinder.

The list goes on, but I don't want to argue every point with every article that has ever been written...

Havasu Living 12-28-2007 03:03 PM

I used my installed AC Sanden compressor. Plan on going with the york setup when and if this one craps out. It's not that hard. good luck

JeepHammer 12-28-2007 04:28 PM

Because of lack of crankcase lubrication, I don't use anything but York for an engine driven compressor.
It's the oil in, oil back out, constantly filling the mister trying to keep the oil trap clean I don't much care for...

If you have a York, then it's economical to use it.
Mounts are already there, install issues are solved. 80% of the work, and 100% of the hard work, is done for you.

If you DON'T have a York, or even the brackets, look into electric compressors.

I don't use a lot of air on the trail, occasional impact wrench for trail repairs, air up/down of tires, blow up air mattress/float toys... You get the idea.
Since I normally have about 10 Gallons of storage, the size of the compressor never becomes an issue.

When I have the back seat in, and I'm towing passengers around, I take the large 5 gal. removable tank out of the bed.
Not a big deal since I don't take passengers on serious trail rides, the two have never conflicted...

The best part about electric compressors is mounting options! Screw them down, plug in the wires, and you are off to the races!
I have my primary compressor mounted under the hood on the fire wall, in that wasted space between the brake master cylinder and fender...

Some guys mount them under the battery/batteries, but I'm not crazy about having my compressor where potential acid leaks will nail it!

Since they only take an 8 Ga. or 10 Ga. wire to run, you can put them about anywhere.
Mounting them on top a 'Carry Tank' has become pretty popular lately, and makes for a portable, compact package.

I carry a loose 'Back Up' that I can clip on the battery terminals in the event of a failure, or I need one in my tow vehicle or loose on the camp site somewhere.
They are cheap and portable enough to do that with...

The choice is yours, but if you are a light to moderate user, don't get hung up on the belt driven only choices.

Something else you might want to consider,
If you do an system install with an electric, all that stuff can be used, usually where it's mounted, If/When you decide to move up to belt driven compressor.

None of it is wasted, not even the electric compressor.
You can always keep the electric as a 'Back Up' to your belt driven compressor.

The funny part is, even the most rabid 'York Or Nothing' compressor guy I've had to deal with on the net finally admitted that his York and be broken for about a year, and he had been using his, 'Electric Backup' for everything all that time!

I've been using an electric compressor in all my little jeeps (light duty/highway use) and in my FSJ/Tow vehicle with no shortage at all in air when I need it!

I have a York on my dedicated off road vehicle, with an electric back up, because, well, you just never know how far out you are going to be when something takes a crap on you...!

Divinitous 01-31-2008 09:15 PM

Just thought I'd add a few comments & my current setup in here.

I've heard of people blowing hoses due to the hot air coming from the York. I wanted to make a setup that I wouldn't have to touch for a good while. When rummaging through Kilby's forum I came across a setup where the person had used aluminum tubing from the York to a manifold on the other side of the engine bay. This was a perfect way to dissipate that heat before it reached anything important.

Another concern was having something go wrong with the system. A broken air hose or a punctured tank would render the system useless until repaired. So I put a ball valve after the air manifold. This would allow me to completely cut out any weak points incase something did happen. Leaving me with the vitals (pop valve, pressure switch, gauge, and a connect point) to work off of.
Everything, except the tank, is designed to handle 250+ psi incase something were to go wrong. So let me wrap this up. Alright, too much explinations. Here's the pictures.

The York is sucking from the airbox. It's cheap, there and I didn't see much of a reason to put one of those small filters in for just the york.

Coming from the york is a 1/2" check valve, 1/2" ID steel braided hose, and 1/2" ID aluminum tubing (heavy stuff .065" wall)

The tubing goes across the engine bay to get rid of the heat from the York.

The tubing then goes to a 3/8" reducer into the manifold which houses all the important mechanical/electrical devices. Directly after the manifold is a ball valve (as mentioned before) and a T. One line goes to the disconnect under the front driver fender (yes I still need to get a cover) and the other goes to the tank.

The tank is somewhere in the 1.5-2 gallon range. I still need to fit a drain valve with a dip tube to pickup from the bottom of the tank. A hose then goes from the tank to a connector inside the jeep.
Update: Over a year later and I do not see any difference in the oil level of the compressor. So it's safe for me to assume that the compressor is blowing by little to no oil. Therefor I'm not worried about a coalescing filer or a drain valve in the tank.

This one is back here cause I have plans to make a pneumatic potato gun. And I wanted to keep the fact that I had OBA somewhat quiet until it was needed.

So there you have it. 2X my budget and a whole lotta time.

Y2KWRANGLER 02-01-2008 09:27 PM


Originally Posted by JeepHammer
I have it hooked to my transmission, transfer case, and axles now also, so my vital components blow bubbles under water, instead of letting in water and dirt/grit.

I just finished my oba project. Can you explain in more detail how this was done? I want my vitals to blow bubbles too.


JeepHammer 02-16-2008 10:44 AM


Originally Posted by Y2KWRANGLER (Post 4761484)
I just finished my oba project. Can you explain in more detail how this was done? I want my vitals to blow bubbles too.


Sure, it's easy.
I unscrewed the regular vents for the transmission and transfer case and screwed in nipples for tubing.
All the tubing comes back to a manifold under the hood, and I use about 5-7 psi out of a pressure regulator to the manifold.

When not off roading and the stuff doesn't need to be pressurized, I vent the manifold block to atmosphere.
The only hard part is running the lines from the rear axle and transmission/transfer case (Trans & T-case are 'T'ed into each other, so there is only one line for both) up to the manifold block.

While I was cleaning, servicing/rebuilding my axles, I did replace the 'O' ring vent hose nipple with a threaded nipple, but I'd think the factory 'O' ring nipple would hold up under 5 to 10 PSI...

Just look at the piping diagram I posed above, and where you see the line with moisture canister going to the distributor, just imagine a manifold block there with lines for the distributor, the front axle, rear axle, and trans. & Transfer case.

I'm now using an electric solenoid to open the air line so I don't have to get out and manually turn on the air from the regulator now, but that wouldn't be a requirement by any means, and they only reason I did it is because I had the stuff laying around and I'm lazy...

PFS 02-26-2008 07:31 PM


Originally Posted by JeepHammer (Post 4592826)
The crank case is sealed so it doesn't let the freon out when you are using it for a A/C compressor, but you need to vent the case if you are going to use it for a OBA so it doesn't force oil into your air lines...
With pressure always trying to get past the rings, it will help control the oil flow into the cylinder.
If the crank case is pressurized at line pressure, every time the piston goes down, it will suck some amount of oil into the cylinder.

I'm getting oil in my air and have been trying to figure it out for a while. This sounds like my problem! What's the best way to vent it?

nic99007 02-27-2008 12:02 PM


Originally Posted by PFS (Post 4870819)
I'm getting oil in my air and have been trying to figure it out for a while. This sounds like my problem! What's the best way to vent it?

:ditto: Same problem and question

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