Smittybilt 2781 Upgrades

[ChrisL]

To prepare for my first BSJ outing I bought the Smittybilt 2781 compressor. I was pleasantly surprised how fast it aired up my tires, but was annoyed with the fact that it ran all the time and there was no easy way to check the air pressure without turning the compressor off. I also did not like Japanese quick disconnect. I found an article online to address all these issues.

Note: You cannot add the quick coupler without adding the pressure switch. If you block the flow the safety release will pop at a much higher PSI which is not ideal.

I added a couple of features:
1 Pressure switch that turns the compressor off at 100 psi and on a 70 psi
2 M12x1.25 x 1/4 NPT converter to use a standard US quick disconnect
3 various fittings and a tee to retain the factory blowoff valve

I removed the end cap of the compressor and found that thin black wire that ran from the motor to the switch and finally to the power solenoid.

Since the pressure switch is normally closed, I snipped that wire and added two wires that I placed through the power inlet plug to the outside of the motor. These new wires will attach to the pressure switch.

I covered the two wires with loom and connected them to the pressure switch.

This completes the wiring, when you turn the switch on, the compressor will build pressure until to 100 psi and then it will shut off. Once the air flow starts the pressure drops and the compressor comes back on. Even though the compressor is rated for 150psi, I chose the 100 psi pressure switch since I do not have an air tank and do not plan on buying one at this point so additional pressure is just strain on the compressor itself.

The plumbing is simple. In the stock configuration, there is a 1/4" NPT pressure relief valve screwed into the compressor output. I needed to extend that connection and add a tee so I could mount the pressure gauge and the relief valve. The reason the pipe is so long is I wanted to minimize the amount of wire on the outside of the unit and I had that piece of brass pipe laying around.

The final upgrade is to get rid of that pesky Japanese quick disconnect. Luckily some enterprising Amazon fellow makes a M12x1.25 to 1/4" mNPT fitting which allows you to install a more generic quick disconnect fitting.

Some of the harder to find parts are here:

M12 fitting


Pressure switch


Pretty easy upgrade and it solved my major complaints about the compressor.

[BlackKnight]

Very nice. I was looking to get a Compressor, was thinking of On-board air, but the Smittybuilt is nice because it's mobile. What's the duty rating on it? can it complete a set of 35"s from ~10LBS to 35LBS within that much time?

Also, are you getting any heat build-up at the fitting that converts it from Japanese to US-style fittings? Where your dropping into 1/4 inch?

[Frank]

Chris , you were right about not buying a tank . A pump that small wouldnt stay ahead of it anyway and I think you did an awesome job of wiring in a shutoff below the max. Mine can do 150 but I installed a off at 130 , on at 100 . I usually turn on the compressor on the way back to the trail head and the 5 gal. tank is full for the first tire . My pump has a 4.0 CFM rating so by the third tire it runs all the time to. I used a clip on chuck so I dont have to hold it while its filling. Youll know when its close. I have a low PSI gauge cause depending on where we are I could go as low as 4psi. (Beadlocks) My low PSI gauge goes to 30 psi max. My high psi gauge tops out at 60. They are more accurate than something 100 or over. Nice job FjR68

[ChrisL]

Bob, the duty-cycle is <finest Chinese technology>%. I was able to fill my 32" tires and another jeeps 32" tires without having it shut off. This is what the website says: Maximum continuous cycle time (Duty cycle) - 40 minutes @ 40 psi @ 75 def F
If you look at that fitting, the M12 fitting is smaller than the 1/4" NPT. If anything this mod increases the flow.
No idea about the heat buildup, I may need a high temp whip installed between the compressor and polyurethane hose. I don't know yet, we will see at the next event when I am trying to inflate my 35x12.50s. I may bring a CO2 tank as backup.

Frank, I ordered a clip on chuck as well. Back in my YJ days on the cape I had a 4 hose contraption that would air down/up all 4 tires at once. I am in the process of building one of those again.
I would have ordered an even lower pressure switch if I could have found one, there is really no reason to strain the compressor/motor since I don't have a tank.

Chris

[BlackKnight]

I was just reading through the specs and some reviews, and it looks like it will even be able to run the 4 tire fill setup I'm planning also. I will be picking one up as soon as I get a new job. (then will work on some of the same mods)

Thanks for the review and information...

[BlackNBlue-ISH]

Looks like a great setup. I like that you are able to just switch it on and move around the vehicle starting and stopping the flow without ever hitting the switch again. What air chuck do you have on the end of the air hose?

I have an MV50 compressor that is similar in concept that I had been thinking of converting to an onboard air setup with a small 1-2 gallon tank to speed up the air-up process. Then again, maybe just getting a legit ARB/Viar tankless setup would be a whole lot easier then that.

[Hoodoo Man]

There was a great write up in JP magazine where they take a similar pump and use a 5-gallon tank as a reservoir. @ Dan, I had a small 2-gallon tank in my TJ and it was worthless as a supplemental tank, I had a york compressor and was still unable to run air tools off of it and never noticed any benefit in airing up, you may want to consider a larger tank the harbor freight 5-gallon tank is about 30-40 bucks and with no back seat in your TJ should still fit easily. I am considering hard mounting that tank on my JK at some point.

@ Chris nice write up and thanks for including links to the cutoff switch!

I may add one of those to my VIAR pump. I've blown out a few hoses as the pump gets very hot near the air outlet on the pump and the constant pressure build-up does not help I am sure.

[RandyCarol]

Both my jeeps have tanks and I don’t think they are necessary if you don’t have air lockers. I do like a small one so the tank is charging between tires so the pump is not cycling. Anybody still running air tools?

[ChrisL]

Right now I am using this tire chuck from Amazon temporarily. That digital gauge is scarily accurate.

I have a long length of 1/4" hose that I am going to build a 4 tire manifold out of with a simple ball valve so I do not need to sit there and hold it.

This compressor is rated at 5.6 CFM but I have no way to measure it.

Chris

[Marky]

I've blown out a few hoses as the pump gets very hot near the air outlet on the pump and the constant pressure build-up does not help I am sure.

That's why I have a stainless steel braided leader hose on mine.

[Marky]

Anybody still running air tools?

I've got a 2.5 gallon tank built into my tool box for air tools. I've got a small variety of tools including a 1/2" compact impact wrench and an angle grinder. I decided to put that in several years ago when we were at Rausch and Jason needed to work on his Jeep. We spent way too long trying to get that bolt loose. IIRC we never did get it off while there. I haven't had an occasion to use it yet (and I prefer it that way) but I'm ready just in case. I have used it in my driveway just to evaluate its effectiveness, and I was able to remove bolts that I couldn't budge otherwise, so I'm fairly confident in the setup.

[Frank]

Mine also came with a braid hose right off the compressor . Id guess 20/24". Id look at another size Chris. I think .25" should be at least 5/16 . Wouldnt you want volume over PSI ? Just so the pump isnt enduring heat the could be passed by ? Why would you want to create PSI in the hose . Its hard to believe that little pump generates 5.6 CFMs . So will that gauge read tire pressure while the pump is running ? I see so many types of fill gizzmoes , yet everyone shuts of the pump to get a reading. FjR68

[ChrisL]

Wouldnt you want volume over PSI ? Just so the pump isnt enduring heat the could be passed by ? Why would you want to create PSI in the hose . Its hard to believe that little pump generates 5.6 CFMs . So will that gauge read tire pressure while the pump is running ? I see so many types of fill gizzmoes , yet everyone shuts of the pump to get a reading. FjR68

Frank, I will show you how this works at the next club outing. Not sure my rock sliders will be here in time for May though.

My inflator (the thing with the digital gauge) will read the tire pressure when you release the hand valve. The problem is most entry-level portable compressors just run when you turn them on. If you stop the flow from the compressor while it is running, it will cause the mechanical blow off valve top pop. That is why I installed the pressure switch. It will shut off the compressor when I release the hand valve and the pressure in the line increases to 100 PSI. This will allow me to read the pressure on the gauge. If I need more air, I squeeze the hand valve, the pressure in the hose will lower and the pressure switch will turn the compressor back on.

A 1/4" line can flow a lot more air than any 12v compressor can realistically generate. Take a look at the following airflow curves here:

https://www.engineeringtoolbox.com/air- ... _1280.html

I am not really worried about restrictions in our application.

While I am skeptical of the 5.65 SCFM rating as well, which is probably at 0 PSI, I have no performance curves to look at. I can tell you that it did inflate my tires quite quickly so I am not sure if I even care about the rating. Honestly, I dislike oilless compressors and am more worried about longevity more then what it accomplishes when new. I am not sure if you have seen this pump before, but it is pretty large and heavy so I have no reason to doubt the performance.

Mark, good point about the leader hose, I may need to install one proactively.

[Marky]

I used to have one of those pumps and actually liked it a lot, except for the non-standard sized valve. I also modified mine, but did not go so far as to put the pressure switch in. I used to let it just pop the safety valve if necessary. It would reset as soon as I reopened the hand valve, so I didn't worry about it. Probably not exactly what it's there for, but... I can also attest to its speed. It is faster than the comparable VIAR models. I sold it to another member when I upgraded to the ARB Twin, which is much faster than all of them.

[BlackKnight]

Here's mine so far, just need to hook the wires to the cut-off. The 4-wheel quick inflation/defaltion rig is just waiting on hose clamps and the valve stem connections.



Did some online checking, w/4-wheel inflate it's ~6 minutes, and 4 minutes to deflate.