The wasp stops here

I haven’t been to the shop in quite a while, but I managed to get over there today around 3pm. My grandpa had been working on the diesel compressor that we use for high-volume tasks such as sand blasting or sometimes spray painting. Over the past year it has been giving us problems to the point where we were ready to junk it (it was built in the 70′s after all). It would start fine most of the time, but then after about a minute there would be some struggling and smoking and it would shut down. When this happened, there was a pressurization somewhere in the engine that would make it impossible to turn the crank at all. After a few minutes, the pressure would bleed off and we could crank it back up again.

The other problem we encountered off and on was a complete loss of compression. We would crank it and then all of a sudden, there was compression and it would fire up and run. This lasted several months, then a few weeks ago it lost compression and we never got it back.

This week my grandpa and one of his renters took the valve cover off, and found that one of the valve keepers was completely broken up in pieces in the bottom of the valve cover. To find a valve keeper, my grandpa went to the place that he bought the compressor from. As of a month ago they had scrapped all of the compressors of the same model…. But lucky for my grandpa he ran into an old friend of his that said there was one more compressor that wasn’t scrapped with the others and was in the dumpster to go out with the next load. It was a 2 cylinder (ours is one cylinder) but the valve components should still be compatible.

So the scrap yard guys tore it apart and retrieved the parts that my grandpa needed for the repair, plus some extra parts- valves, keepers, rocker arms and push rods. The keepers worked great. We put the engine back together and fired it up. There was plenty of compression and the tank came up to pressure wonderfully, but just as it reached full pressure, white smoke poured out of the exhaust, and the engine died. The culprit was the mysterious over-pressurization.

After some discussion, we decided that it must be the compressor intake cutoff, and took that part off. Everything seemed to look good, we sprayed some blaster in it, moved the plungers, put it back together, and fired it back up. Same result. Stall with over-pressurization.

Still determined that the intake cutoff was the problem, we decided to pull a bolt that appeared to set the pressure for the cutoff. When we started to clean it, a hole appeared where we thought the bolt was just dirty. It turns out that a mud dobber had covered this hole, which was the atmospheric relief for the cutoff regulator. We put it back together and it started, and cycled the cutoff just like it did when we first bought it over 10 years ago.

It amazes me that a simple stinging insect can plug a hole with enough mud to resist over 100 psi of pressure, and send us on a wild goose chase to fix a 40 year old compressor. As I told my grandpa- it is great that these older machines are so simple to fix, but the catch 22 is that when a problem like this comes about, that simplicity compels you to fix it, even though it turns into a long drawn-out project!