Vintage Compressor Crankcase Fitting

[mrtonegto]

It's an old Curtis from 1942. Wondering what is the purpose of the 1/4" copper line running to/from the crankcase?

The opposite end is now unattached and was probably associated with the original unloader system. Should I cap it off or leave it open like a breather?

 

[kams1973]

It's a crankcase vent. It would've been plumbed from the side access cover on the crankcase to the intake of the first stage cylinder.

 

[mrtonegto]

Excellent, just got that done.

Thanks