Airmax Compressor Tuning

It costs most people about $1700 to get a Shoebox up and running with clean dry air.  Similarly the Chinese Airmax compressor imported by Mrodair also needs some additional stuff and ends up at a similar cost.  

To set up an Airmax you need:
The compressor ($975)

The upgrade kit on this page ($260)

Post compression filter ($275 for Jaimee's on the Talon forum, or $400 for Joe B. unit)

Upgraded power cord and switch ($60)

Chemlube 501 oil guart ($35)

total investment: $1605 or $1730 based on filter choice.

If you need to run it every day, save your money for a Bauer.  But another point to keep in mind is when a Bauer eats a piston or throws a rod, and it happens, that's an $1800 repair, so really in a sense if our Airmax down the road someday tears itself apart we'll be looking at a thousand dollars to fix the problem by buying another one.  So the Airmax is not a bad option for those of us that want high speed fills on an under $2k budget.

Cylinder honing to control oil flow FREE if you send them to me when buying a kit, or look below on how to buy the tool and do it yourself.

Airmax upgrade parts kit $260 shipped USPS Priority mail
•  larger reed valve plate made from 303 stainless ($16.25)
•  1/2" thick aluminum head tapped for air filter ($7)
•  intake air filter  ($7.25)
•  1st stage head gasket to replace wimpy oring  (All gaskets add up to $10)
•  Longer head bolts to fit the thicker head  ($4)
•  anti-seize compound  ($1.50)
•  power cord strain relief/water pump mount plate  ($5)
•  A replacement oil drain plug (the original can disintegrate) ($2)
•  All the orings used in the compressor including new high temp. 2nd stage head gasket o-ring (there is one o-ring in the compressor I'm working on having custom   made and when we get those figured out I'll send you a couple) ($5)
•  gaskets for both sides of new reed valve plate
•  parts for waste water cooling system (garden hose hookup) ($8)
•  USPS Priority Mail   ($14)

total: $80.00
If you're willing to pay me $20 for doing the shopping for you, the total parts and shipping cost is $100

It takes me pretty much 2 hours of time at $80/hour shop rate, so that's $160

Total kit price: $260

If you want me to hone your cylinders to control oil flow, send them to me and I'll do it for free and send them back with your kit.

If you are local to me and want to bring your compressor for me to do the upgrades for you, figure on one hour of shop time which is $80.

Email me (and Paypal) at This email address is being protected from spambots. You need JavaScript enabled to view it.

Files to make your own gaskets, intake head, and reed valve plate:
Note: The high pressure cylinder has a paper gasket, but the area it seals is the cylinder for a large diameter piston looking thing.  It's job is to move the small diameter actual pressurizing piston up and down, and that bigger piston looking thing actually has a hole drilled in it to vent to the crankcase.  So that seal is really only a spacer and a non-pressurized oil seal and doesn't need changing.


Gaskets Parts
Water cover gasket Head drawing
Upper reed valve plate gasket Reed valve plate drawing
Lower reed valve plate gasket Head and Reed Valve Plate dimensions
Head Gasket  


O-ring list tested and fits (from
2nd stage head 3mm X 16mm Metric Buna-N 70 O-ring (N3.00X016)
or a higher temp option: M3x16 Silicone Rubber O-Ring, 70A Durometer, Round, Red, 16 mm ID, 22 mm OD, 3 mm Width (Pack of 25) (at Amazon here)
separator inlet fitting N1.80X011.2 Buna-N 70 O-ring (N1.80X011.2)
water jacket 2.5mm X 53mm Metric Buna-N 70 O-Ring (N2.50X053)
water jacket 2mm X 5mm Metric Buna-N 70 O-ring (N2.00X005)
media holder: 3mm X 17mm Metric Buna-N 70 O-ring (N3.00X017)  
Moisture separator poppet valve: 2mm X 5mm Silicone O-Ring 70D S2.00X005

Use waste water cooling instead of bucket pumping.  Much easier, smaller foot print when stored, constant water temperature makes for cooler runs.  Adapt from garden hose to 5//16" barb for inlet.  TIP: When finished blow the water out of the heads by blowing on the end of the return line. 

You might Install an hour meter (cheap off eBay).

Make a new power cord out of 12 or 10 gauge wire.  You can just buy a 30 amp extension cord and cut the female end off and an extra foot for running from the switch to the motor.

Change the power switch for a 30 amp wall type switch from the hardware store.

You will need a 30 amp breaker for your power supply, wired to the correct kind of outlet.

The low pressure head water seal consists of a thin o-ring around the intake hole and RTV around the rest of the head, making it a pain to remove/replace since you have to use more RTV to glue it on.  I replaced it with a head gasket.

The cheap airline the compressor comes with probably won't fit anything, and I don't trust it.  I got a foster male fitting for the hole in the moisture separator and use my good hose.   The only source I've found for a  a male Foster x 1/8" BSPP to screw into the moisture separator instead of the airline is Rapid Air Weapons

Tighten the motor mount bolts.  They all come loose and it's not for vibration control, that big rubber pad will work just fine with some tighteness on the bolts.

Remove the worthless molecular sieve material from the moisture separator and put some paper towel in there as some absorbant.  The quality post compression filter you added will do the yeomans job anyway.

Don't lubricate the high pressure cylinder's oring with silicone or SuperLube the way we usually handle orings.  It gets so hot it will drive the grease like steam into the rubber and make it swell.  I'm thinking either dry or wet with the crankcase oil.

The 2nd stage rings have a spreader ring under them.  The spreader rings are randomly placed.  They are better placed so that their gaps line up with the compression ring gaps to provide maximum spreading force.  Clock the sets of rings so that no two line up. 

The cylinders are not honed and may pass excessive amounts of oil.  It is recommended you hone the cylinders with a 240 grit Flex-hone, about $24 on eBay.  Search for 1-5/8" 240 grit Flexible Cylinder Hone.

If you don't do these upgrades, you will do them in short order as occasion demands, so don't get mad at the unit.  You've been warned: it comes with the usual cheap o-rings and gaskets we've come to expect from equipment made in this part of the world. 

Cutting in hour meter:
Trace opening size with a fine point Sharpie pen.  Drill holes in the corners such that the edges of the drilled holes are just short of being tangent to the traced lines.  Cut opening with a Dremel type rotary tool using a fiber cut off disk like Gyros 11-41502 1 1/2" diameter.  Put paper towels underneath to collect dust.  File as necessary to smooth edges and adjust opening size.

Wiring Diagram for the Water Pump Switch (if you choose to use a pump instead of waste water cooling):
(Different label on this switch.  I grabbed the image because it shows the terminals.)


Note about Oil: 
Expensive compressors (Bauer et. al.) use high flash point synthetic oil to prevent burning of the oil and the resulting carbon build up in the high compression cylinder which necessitates frequent tear downs and cleaning. 

A high pressure air compressor is basically a diesel engine when operating with standard petroleum air compressor oil.  It burns that stuff like crazy and it is the combustion by products that build up around the piston rings, poppet valve and reed valves of the high pressure side, and therefor require frequent cleaning. I'm using Chemlube 501, often used in Bauer.  It provides 8x longer cleaning intervals because it has a higher flashpoint and doesn't combust like the hardware store oil.  It does create a light black soot which over time also needs to be cleaned, but much less frequently.

I removed the rear crank case cover and removed all the original oil and gave it a wash with some brake cleaner.  I opened up the high pressure head, line, and separator to clean them of carbonized oil. A quart of Chemlube 501 costs about ~$33 shipped. I sourced it on eBay from this vendor:

Hot climates may choose to use Chemlube 800 (40 weight oil instead of 501 which is 30 weight).  The 800 product is recommended for tropical locations where the oil starts out hot and thin to begin with (so hopefully sun baked 40 weight oil is thinned to behave like a 30 weight on starup), but is only available in gallons.  The Airmax compressor has the standard small engine bearing-less setup which is basically like an auto engine without the additional soft metal 'bearing' (our connecting rods are already made from a soft metal: aluminum).  Such a bearing system (same as in a car) relies on a thin film of oil to prevent the soft bearing and hard crankshaft from actually touching each other (which would cause galling, or the transferring of the soft material to the hard material).

Also keep in mind Bauers have needle bearings that are in contact with surfaces, while bearing systems like Airmax rely on an oil film preventing metal to metal contact. Oil too thick when cold can cause metal to metal contact until the oil drops in viscosity and generates the thin film required between the parts, but conversely oil that is too thin at start (like say 30 weight oil in a tropical environment in the sun on a boat deck) may allow the oil to run out of the bearing gaps allowing metal to metal contact until the oil is pumped around.  

The only important thing is don't use compressor oil from the hardware store intended for 100 psi compressors, and don't use slick marketing b.s. products like Royal Purple.

Moisture removal/filtering:
There are basically three types of compressed air dryers: desiccant, chemical and refrigerant. Each of these dryers reduces the dewpoint of the air with varying degrees of efficiency and economy. Dewpoint is the temperature at which water vapor will begin to condense at a given air pressure. The refrigerant method relies on the cold surfaces of a chamber on which the moisture condenses out. The larger the chamber, the more cold surface exposed to moisture ladden air and the better the moisture extraction.  It's called refrigerated even though it's not actively being refrigerated because the delta T, or difference in temperature between the air and the warm refrigerated chamber's walls can be as significant as room temperature to a refrigerator.

Parts I used (note when searching on eBay to click the button on the left to 'show US only' to filter out all the Chinese locations.  You'll be buying the same products, but much faster to get them from a US supplier):

Compressor Oil: search eBay for Chemlube 501 ~$33 shipped

Hour Meter: search eBay for Hour meter 110v $12.50 


1/8" BSPP x male foster to replace the questionable quality fill hose with a fitting that will allow you to use the quality microbore double female hose I'm sure you all already have for your tank.

Available from Rapid Air Weapons


Airmax Mods

  • IMG 7163
  • IMG 7160
  • IMG 7159
  • IMG 7158