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timatoe 08-24-2008 10:40 PM

'90 4.2 W/Serp. OBA Build
This is my attempt at a write up for On Board Air for my ’90 4.2 without A/C with a serpentine belt. I haven’t seen any other write ups for this setup.

I picked up a York 209 from a guy on craigslist for $25. I used a lot of different write ups from the net to break it down, clean it up etc. so I’m not gonna get into all that. I used a gasket kit from Napa for the rebuild part# 207120, the kit has gaskets for the 206, 209, & 210.

Stock Bracket on the 4.2 without air and serp. belt.

And without the idler.

I thought I’d be able to fab up my own bracket, but quickly realized it was going to be way more work than I was willing to do. So I called Kilby Enterprises. Then I e-mailed them but I never got a response back from them. They don’t offer a kit for the 4.2 with serp. on their site and apparently don't offer help if you're not gonna drop alot of money. I did find somewhere on their site that showed using an A/C bracket from a CJ. So, I decided they didn’t want my money and called J&W Jeep in Antelope CA. I went down a picked up the bracket for $50. I don’t know if this number would help anyone finding the bracket but it has a cast number of 3237579.

Here’s the bracket as I got it.

I bought a new 6 groove clutch from a seller that sells compressors, cluthes and what not for big rigs on eBay for $61 to the door. Unfortunately I forgot his name and it’s not in my eBay profile because I bought it direct.

On the York I left the incoming line the same as it came.

On the outlet side I cut the nipple off and tapped out the head to ¼” NPT.

Then used a compression fitting and connected a five foot section of copper tubing, that then got ran into the filter and check valve with a leader hose from there into the manifold.

timatoe 08-24-2008 10:41 PM

I used a piece of angle iron mounted to the top of the compressor to hold the manifold. I drilled a hole in the back and then attached the leader hose to the back there. The rest of the components are general OBA type stuff.

I pulled all of the original alternator mounting bracketry off and the CJ bracket bolted right up. But I couldn’t get the alternator to bolt up and be able to still move for belt adjustment. So I cut off part of the new bracket, you can see it here.

Once I had the alternator mounted I figured out that none of the stock stuff would go back in and I had no way to hold the alt. in place. I went to Kragen and bought a generic GM alternator bracket Spectre #4226 for $13. It was WAY too long so I cut it down to work for me.

I still had to trim the inner fender just a little to allow enough clearance to tighten the serpentine belt. I ended up using the Goodyear Gatorback #4060760 which is a 76” belt, the stock belt is 81”.

timatoe 08-24-2008 10:41 PM

I used ARB type hose to come out of the manifold and through a bulkhead connector into the cab. Then into the 3 gallon tank that I mounted on the rear fender well.

I made a new switch panel that was inspired from one I saw on It’s got a switch for the air and two for winch controls, now I just have to convince the wife I need a winch to go with the switches.:thumbsup:

And a somewhat complete list of parts.

York 209 Compressor $25 Craigslist

Viair Leader Hose $12

Viair Safety Valve $6

Manifold 5 port $5 Truckload tool sale

Pressure Switch $13 110/135

Tank $33 3 gallon

York Gasket Kit $20 Napa

Bracket $50 J & W Jeep

Serp. Belt $32 Kragen

6 Groove Pulley $61 eBay seller

Hose & Push In Fittings $34

Alternator Bracket $14 Kragen

3/8” SMC Check Valve $13

3/8” SMC Filter $25

Various Fittings,Bolts, Etc. $50 (roughly) Lowe’s, local hardware store.

That’s pretty much it. Hope it helps someone.

Oscar_P 11-27-2009 01:16 PM

What is the fitting going throught your firewall connected to the blue hose in the fourth to last picture. I'm trying to figure out how to get mine through the firewall also.

timatoe 11-27-2009 04:15 PM


Originally Posted by Oscar_P (Post 8367287)
What is the fitting going throught your firewall connected to the blue hose in the fourth to last picture. I'm trying to figure out how to get mine through the firewall also.


Originally Posted by timatoe (Post 5614456)

And a somewhat complete list of parts.

Hose & Push In Fittings $34

Bulkhead Union -

I'm 99% sure I used 3/8" hose.

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