I recently bought a "PAR" air compressor, model "15", manufactured by the Lynch Manufacturing Company of Defiance, Ohio in 1945. It has 290 degree opposing pairs of low pressure and high pressure cylinders (4 cylinders total) in a cast iron block. It is splash lubricated, and the reed valves sound fine through the cylinder heads. The motor is a 2 HP 120 VAC Baldor, and is clearly not original. The original motor mounting plate is very large relative to the Baldor, and the shives are 2-belt, which to me means 7.5 to 10 HP. Also, the Model "15" nomenclature sounds like it might mean 15 CFM, which this compressor is clearly not doing at present. 7 or 8 CFM tops, right now.
The Baldor is 1750 RPM, and the shive looks like it could be orignal. I was thinking of putting a 3550 RPM 7.5 HP motor on the compressor to get the flow up to where I think it probably was originally intended to be. I'd like to run a large blasting cabinet with this unit, and at present it's not up to it.
My questions are:1) Should I re-shive and stay at 1750 on the motor, or go to 3550 RPM on the motor?
2) In terms of maximum crankshaft rpm, is there a rule of thumb for old cast iron compressors heads?
Thanks very much for the help! Dave