Lubrication for Yong Heng rebuild?

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Piston, rod, rings, etc. kit has arrived from China for YH attempted rebuild. Any advice on pre-assembly lubrication would be appreciated. Have lith grease, moly paste, etc. not sure what to use or what’s necessary. Got plenty of hydraulic oil for crankcase. It’s the upper I’m thinking about. (Photo is broken part being replaced for reference). Thanks
 
I'd use synthetic Air Compressor oil vice hydraulic oil. As far as the upper (high pressure) piston, rings and cylinder, use NO LUBE at all on that section. Just clean it well, ensure it is lint free and assemble dry. The lower (low pressure) piston, rings and cylinder just a very light coat of the air compressor oil. Better to have LESS than MORE on these HPACs...
​Mike
 
update: BIG FAIL
The piston rod on my Yong Heng seized. There is a dipper on the rod that mysteriously broke, thus depriving the crankpin of oil. I ordered a new piston assembly from Ali Express for only $20 BUT…… The new assembly second stage piston did not fit in the Yong Heng. The new part had 4 plastic rings, and the original had three. They looked identical in diameter, but in fact the new second stage piston was a few thousands too large. “Okaaaaaay…..” sez me. “We’re not done yet.” I took apart the new assembly and moved the new rod to my old original piston set to replace the original rod that seized. This time the reassembly went smoothly. But after about a 3 minute run under no load to wear in the new rod I got a catastrophic failure. The failure point was where the first stage and second stage pistons are connected. I tried hard, but I’m done with Yong Heng. Even if yours runs great for a while, it will need a rebuild. I could not find a reliable source of correct parts. Without that, you’re screwed at some point down the road. 
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Did I make a big mistake? I bought a Yong Heng compressor from China!![/QUOTE]https://www.airgunnation.com/topic/...mpressor-from-china/embed/#?secret=gWgcXFaT3k
 
Hi, I just tried my brand new YH compressor and after about 10 minutes, it started making seizing noises, so I shut it down. I think the issue is going to come down to using the #46 hydraulic oil instead of #46 compressor oil. There could be a difference. I'm not sure what exactly went wrong yet, but I smelled a burned oil smell when I shut it off, or burned something. and the oil was gray when I drained it into a jar. 
Your problem may have been that the new 2nd stage piston was over size and putting the old one into the new piston top hole, was probably too loose of a fit or maybe you didn't get the retaining clip ,or whatever holds it in, seated properly. Anyway, I would like to get your replacement connecting rod from you if it is still in good cond, or maybe the whole compressor, if you are done with it; if so give me a price. I'm in CA....where are you?
My email: stevealexanders at netzero.net. replace "at" with @ and remove spaces