Compressor Refurbishment – Part 2

Time to tear down the compressor itself. Of course, I waited until I got stuck to find some directions, so this may not be the most sensible order of things, but here we go.IMG_2337.JPG

I started by draining the oil and removing the oil filter. This unit conveniently has a length of pipe that takes the drain plug over the edge of the tank deck. I’m not sure if that’s present on all units, but certainly handy (and an easy install if it’s missing).

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Wow that oil looks gross. Clearly has both water and rust in it. The open bottle on the bottom of the picture is underneath the oil drain, I should have pulled a bin out and put it under the filter location, but I didn’t realize how much oil had been forced up into the hydraulic unloader when I ran it.

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Pulled off the crankcase cover — look at that seal. These are all paper seals, and they are tough. You can also see the crankshaft and connecting rods chilling in there. From here I took a winding detour that included pulling off the hydraulic unloader, unbolting the head, rebolting the head back on, putting the hydraulic loader back on, then using this guy’s trick to get the last connecting rod bolt out.IMG_2523.JPG

Everything is out now, except the crankshaft. You can kind of see the bend it in here. While it was still installed, I decided to measure how bent it is. Pulled out my Noga indicator base (possibly the greatest invention since sliced bread) and popped a cheap Fowler indicator into it, resulting in around 125 thousandths of runout — in other words, 1/8″!

There are a few options at this point:

  1. Buy a new crankshaft. I haven’t asked Quincy or one of their distributors for a quote yet, but some quick trips to my favorite sites for this project (and most of my projects, honestly) — Practical Machinist and Garage Journal — suggest it’ll run $800+. Thta’s more than I’m willing to spend, considering some patience would probably turn up a 325 with a good crankshaft to drop into this for less.
  2. Try to bend it back with my hydraulic press. This seems like a bad plan, as it’s a cast iron part (note the texture of the unmachined surfaces). It will probably crack. That also means I can’t…
  3. Weld a new shaft on. I could braze one on, but I don’t have brazing equipment or any experience brazing. This is a fairly tight tolerance application, so I’d rather not try something new this time.
  4. Turn the end of the shaft down so it’s straight, then make a spacer to fit the pulley back on.

I’m going to start by trying number 4, which means checking whether this thing will even fit on my tiny 10″x33″ lathe, and then figuring out how to get it mounted for turning.

Compressor Refurbishment – Part 1

I’ve been looking for the best way to get more compressed air in my shop for a while. In the near term, it’s because my mill can keep my California Air Tools 1HP unit running pretty much constantly when using air blast, but in the long term I’d like to be able to paint or sandblast, run air tools, etc.

The other factor is that since this is at my house (which is next to a public park) it’s gotta be quiet. A truly quiet unit with a rotary screw compressor is out of my budget, even used. Pretty much everyone agrees that the best option for a quiet (and durable) reciprocating piston compressor is a Quincy 325. So I started my Ebay hunt, and after a few weeks turned up the unit above for $180 (plus freight, which ran me about $250).

Once this thing showed up, it was in sorry shape.

  • Air pressure gauge busted.
  • Motor burned out.
  • Rust on pulleys and water inside the compressor air lines (possibly inside the compressor itself).
  • Pressure switch snapped off.
  • Tank is very rusty inside.

The first order of business was to see if I could get everything working, which started with putting it somewhere I could work on it inside. That meant adding wheels, which I welded on with my AlphaTIG 200X, using the stock SMAW setup and 6011 rod, running at about 90 amps (DCEP).

The next step was rebuilding the entire electrical system , putting in a new motor, and trying to turn the unit on (with the tank uncapped, more on that later). Since I’ve only got single phase, I picked up a 4kW VFD which takes single phase input and provides three phase output. This is a cheap Huanyang unit (actually a rebranded or knock off unit made to the same specs, based on the manual and some Google-fu), but I expect it will do the job since I don’t expect to push this unit very hard. I also checked the crankcase oil level and filter, both of which were fine (although the oil is milky, I’ll replace it and the filter later), and replaced the air filter with a low-noise intake from Solberg.

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All together and ready to run. That galvanized box on the right hand side has the VFD and breaker in it, and you may have noticed the shoddy wiring job to my welder outlet. That’s just for testing.

Turns out the crankshaft is bent. Apparently a common issue with this units if they’re shipped improperly, because they’re top heavy. I wouldn’t be surprised if this unit would last for years for my needs running in this condition, but it’ll definitely shorten the bearing life, and probably the belts’ lives as well.

Guess it’s time to tear the unit down the rest of the way. It’ll also give me an opportunity to inspect the internals and replace anything that may have an issue.