The Superflow MV50 is a perfectly capable little compressor, particularly when price and portability are considered. After using mine for a few years and exploring the thermal cutoff more than once, the compressor simply took far too long to air up my 33" tires. On the last trailride prior to these modifications, it took nearly 25 minutes to get 4 33" tires from 18psi to 35psi.
I wanted to find out whether there was anything wrong with mine, and whether I could do anything to get sustained flow again. For disassembly, all that is required is a 4mm allen wrench or driver for the head bolts, and a 14mm wrench for the output fitting.
Disassembly of the compressor piston and head takes a minute. Once the four studs are removed, everything else can be removed by hand. Not surprisingly, when I pulled the piston head off, I found very visible signs of overheating. I cleaned up the piston, the skirt, and the head, and used a very thin application of high-quality grease on the piston.
After studying the head for a few minutes, it became obvious that there was room to port the intake and output ports. Each port is covered by a flexible steel flap, and when the piston is on the downstroke the flap opens to allow air in to the chamber. Then when the piston is on the upstroke, the compressed air forces open the output flap. These flaps make excellent templates for the porting.
Using a router bit on a Dremel, I removed the rib and a bit of extra material on the intake port for a roughly 25% gain in flow capacity. I used the Dremel to effectively double the size of the output port.
After a good cleaning, I reassembled the compressor, and using parts from leftover projects installed a brass, barbed output; and a new coiled hose (the original hose fittings leaked at the assembly that is screwed onto the valve stem). Then I sourced a zooty Type R filter to replace the original plastic and sponge filter for more airflow and a touch of bling.
The MV50 is rated at 150 psi and 2.5 CFM and when new, it could inflate a 33" tire from 18psi to 35psi in roughly 3 minutes. After this cleaning and porting, the MV50 sustained airflow over multiple fills and consistently aired my 33's from 18psi to 35psi in just over two minutes per tire. This is a very satisfactory result for 1 hour of time and $7.
Please see the Superflow MV50 gallery for full-size pictures.