Resurrecting a used Max Air 35

[toddster541]

I recently picked up a used MaxAir 35. This unit was new in 2006 and allegedly has less than 50 hours run-time (the hour meter battery had gone dead.) It has mostly been riding around, bolted to the deck of a sailboat in the Sea of Cortez, or sitting in a garage, since then. The previous owner had the Honda motor serviced and all of the rusted bits, including the carb, replaced by a small engine shop about a month ago. It seems to run fine, although the max RPM I get from it is about 3200 instead of 3500.

I've cleaned up the compressor, replaced the hose, gauge, hour/tach meter, and a few missing frame screws. Changed the oil, which looked clear, but there was a streak of dark matter that pooled at the bottom of the pan - not course enough to recover any particles - more like a bit of soot.

So: it pretty consistently takes 35 minutes to fill an aluminum 80. Which works out to more like 2.3 cfm than 3.5. The 10% low motor RPM can't account for that much loss. Belt tension seems OK, but I haven't put a new belt on. The back pressure valve opens at 1000 psi. The relief valve opens at 3000 psi, rather than the 3300 it is supposed to be set at. If I pump it up to 200 bar (just before the valve opens), I can't find any leaks around any of the fittings, using soapy water. But still it gradually leaks down over about an hour or two. I kind of suspect the relief valve, since after opening, it gradually sorta closes when the system leaks down to around 2200 but there doesn't seem to be a definite shut-off. Though I don't get soap bubbling on the outside of it. Not sure what the normal behavior looks like for this valve.

Since I'm currently using aluminum 80's and rarely need to fill more than two tanks in a day, the compressor more or less is doing what I need it to do. So I don't wan't to start throwing expensive parts at it. But it doesn't seem quite right...

Any ideas what to try next? Don't worry, be happy?

 

[toddster541]

Well, I am revising my opinion about the belt tension. After taking off the guard and actually measuring deflection, it was at least twice what the manual calls for. (5mm deflection from 5 kg force. Very tight.) The motor was already at the limit of its adjusting slots. And the bracket under there was covered with black dust. Time for a new belt!

Belt specification is A31.5 13 x 800 mm. The PO had supplied a spare belt, but curiously, although it was also marked A31.5, it was at least an inch longer than the old one! So I raced over the mountain to NAPA, and the equivalent belt they came up with was also about an inch longer. Hmm... I'm wondering if there's some sort of inner diameter vs outer diameter discrepancy between here and Italy... Anyhow, sorted through the stack and found the next slightly smaller belt (4L330). Got it on and tensioned, using a couple of screw-clamps and some "english."

Man, a piece of gear this expensive ought to have a mechanical belt tensioner!

Now I will have to arrange to empty a tank or two in the near future, so I can see if this made any difference.