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Discussion Starter · #1 ·
After reading a bunch of threads regarding this little sub $50 compressor, I bought one last September. It's been used about a dozen times and it's been great... until last Sunday. On my last tire, the pump suddenly changed tone drastically and I noticed the pressure gauge wasn't rising anymore. It actually starting dropping pressure! I know something went bad and guessed that one of the reed valves was messed up.

Yesterday, I did some searching on the net and found several people modding the pump. In one thread, a guy described a failure exactly as I had. He tore apart the pump and found a reed valve pulled into one of the ports. When I got home, I pulled the pump apart and sure enough, one of the reeds had blown a hole the size of the port in it. :violent1:

Fortunately, modding this thing and replacing the reed with something more durable isn't a major task. I'll write up a summary regarding the mod. In the meantime, beware that this pump may be good when it's working, but the reeds are a POS.

 

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Discussion Starter · #2 · (Edited)
Finally got around to modding/fixing the compressor. This pic is of the destroyed reed valve. Nice, huh?



After grinding off the rivets holding the reed in place, this is what the reed looked like. If you notice where the reed contacts the valve block, you'll see there is a recessed area that no doubt contributes to the reed getting stress cracks and eventually failing. Oddly enough, the other reed on the other side of the valve block seems to seal against an o-ring. There was no o-ring under the failed reed. :confused:



The stock reed was 0.004" thick.



The valve block wasn't very flat, so I decided to surface it. Some people opened up the intake port on other threads I've read on this mod. But, one guy opened it up too far and ended up putting a hole in the reed he installed. I just decided to break the edge of the port and smooth it out with a wire brush on my dremel. I wanted the mating surface to be smooth and didn't think there would really be that much of a performance improvement by opening the port up.



I took a dremel and beveled the port on both sides. This pic is of the opposite side of the valve block. You can see my horrible dremel work on the port and the stock exhaust reed, which seems to still be in good shape.



I took a 0.005" feeler gauge and cut it to size, then used a punch to mark the hole location. This is the new reed sitting on top of the valve block.



I drilled a hole 0.090" dia so I could tap it for a #4-40 machine screw.



Installed a #4-40 cap screw and used red loctite to keep it there.



At this point, I reassembled the compressor and went out to test it. When I turned it on I heard a LOUD knocking sound. OOPS - I forgot to see if there was enough clearance between the cap screw and the piston. There wasn't and fortunately, the screw made a nice indentation on the piston for me to see where I had to grind the piston for clearance. Here's the piston ground with my horrible dremel tool skills.

The area I had to grind is on the center-right of this pic. There's a rectangular area in the piston that I had to grind the upper-right edge away.




While I was at it, I pulled the rest of the compressor apart to see if there was anything else worth modding. The wiring actually looked much better than other pics I've seen, so I left it alone. I cleaned and lubed the piston and cylinder using molybdenum grease. It seals the piston very well and now pumps so well, the pressure gauge max's out. I plan on oiling the compressor every other use by putting a few drops of oil into the intake port. That should keep the piston sealed well. I also noticed that the connecting rod lower had a sealed roller bearing on it. That's kind of nice. I won't have to mess with that at all.

Once I put it all back together, it worked great. Total cost for this mod was less than $20. I had to buy the tap (needed a new one anyway), the screw and a new feeler gauge set (which I needed as well).
 

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Thanks for the reviews so far. Air compressors are definitely on my "to get" list.

Looking at the Viairs but a little on the expensive side for me.
 

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I have the same pump. Mine melted the fuse holder and melted the wiring on the second tire I tried it on. I read up on it ExPo, toyota and other forums. Turns out tons of others have had the same exact failure as mine. I rewired the whole thing with 10 awg wire and a 30 amp fuse/holder to fix, as recommended by a bunch of other folks all over the interwebs. Disappointing to say the least.

If I were to buy again, I'd be buying the Heavy Duty Harbor Freight one. Its the same price, and far less problems.

FYI Buyer Beware.
 

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I have one of these $50 specials, which has worked better than I anticipated for a "disposable" compressor. [I have run York and Sanden engine driven AC compressor based OBA systems, as well as a Thomas 12v 1/3 HP continuous duty compressor system, which allows me to make a seat of the pants comparison.]

There is a substantial jump in price between the MV-1050 and the entry level Viair, ARB, etc., without a corresponding jump in rated performance, which makes the MV-1050 a good buy for the typical weekend warrior. However, they are a bit slow for 33" tires.

As noted in a post above, the cheap price is sometimes accompanied by cheap assembly. It would be a good idea to pull the cover for the wiring and ensure that the connections are properly done. If you like to tinker, for just a few dollars you can increase the gauge of the power cord, use a 35 amp circuit breaker in place of the fuse, and tap the head for standard 1/4" NPT fittings. [All these mods can easily be switched over to another unit if/when you burn up your first one.] Also, always use these units with the engine running so you get full voltage from your alternator - the voltage loss when using the battery alone reduces the compressor output substantially.
 

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nice. i really like mine. i've had no issues with it yet, used it about a dozen times now
 

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Discussion Starter · #8 ·
bump for mod write up in post #2.
 

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Thanks for the reviews so far. Air compressors are definitely on my "to get" list.

Looking at the Viairs but a little on the expensive side for me.
They are BUT...put one in your cart (Amazon Prime) and wait awhile. It'll
eventually show up as a "deal of the day" or your Gold Box item. Got mine
for 47% off...shipped in 2 days. Tip worth sharin', no?! :rockin:
 

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Discussion Starter · #11 ·
If you look at the reviews on amazon the manufacture has actually improved the design a little bit, they now come with a quick connect that is more common and other little things...

still havent used mine yet... hope i never do lol..
BTW - I noticed on mine that the quick connect for the air line was already a standard fitting. I thought is was some one-off chinese/metric one, but it turned out to be a standard fitting. I can use whatever air hose I want...
 

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They are BUT...put one in your cart (Amazon Prime) and wait awhile. It'll
eventually show up as a "deal of the day" or your Gold Box item. Got mine
for 47% off...shipped in 2 days. Tip worth sharin', no?! :rockin:
Dude.. 47% is a helluva deal! Thanks for the tip. I have mine in the Wish List instead of the cart.. hopefully it works the same :)

OP - good write up! You should make a thread in the how-to section as well since this thread might be lost in a few weeks.
 

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I have the same pump. Mine melted the fuse holder and melted the wiring on the second tire I tried it on. I read up on it ExPo, toyota and other forums. Turns out tons of others have had the same exact failure as mine. I rewired the whole thing with 10 awg wire and a 30 amp fuse/holder to fix, as recommended by a bunch of other folks all over the interwebs. Disappointing to say the least.

If I were to buy again, I'd be buying the Heavy Duty Harbor Freight one. Its the same price, and far less problems.

FYI Buyer Beware.
Well, mine died this morning. Into the trash can it goes. The pump had bees nothing but problematic since the day I bought it. I will NOT be buying another one of these. :( ymmv
 

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Discussion Starter · #15 ·
Mine works but I noticed the little fuse holder thingy has totally fallen apart...Not sure how. The fuse is really what's holding it together now. Going to look at fixing that at some point...
It's frustrating to buy products that aren't built well. In the case of this particular compressor, it seems the motor itself is decent and will last. The weak links are the wiring and the reeds. My wiring is in good shape. I'll probably redo it at some point though.
 

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Discussion Starter · #17 ·

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There is a thread on ExpeditionPortal.com discussing how to frankenstein a MasterFlow compressor and Harbor Freight unit to use the best parts from each.

You are correct that the head and piston are identical. The poster commented that the motor in the Harbor Freight unit was put together better than the MasterFlow, but most of the parts are interchangeable.
 

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