i had a free minute today so i decided to give my pump some attention.
tear down is very easy to get at most of the goods. simple take off the top four "cylinder head" bolts. then the head flutter vales, cylinder and jug heatsink come off leaving you with a view of the piston assembly.
i haven't noticed any drop off in performance but i figured a tare down would be fun. i found quite a bit of dirt in mine and some scoring on the cylinder walls. the cylinder wall issue is strange as the "piston ring" had deformations but nothing that correlated with the walls. my guess is there was dirt or manufacturing debris to blame thats has sence passed through the system. the good news is if you flip the cylinder over you get fresh walls again as the piston only uses the top portion.
slime air gauge mode- not really happy with this...it flutters back and forth while the pump is on so its impossible to get even a idea of where your at while inflating. you have to turn off the pump to see what you have. the old guage may be going back in. at least i knew that when it read 45 it ment i was at 40 psi. sure the slime is more accurate, but if your airing down you most likely are already carrying a decent tire gauge. oh and by the way at first i bought a replacement air gauge at harbor freight. when it fluttered like crazy i figure it was just cause i had bought a cheap version since there was no mention of this behavior from others that had done the mod. so...i went out and bought the slime version and its exactly the same gauge
here is a picture of the cylinder and the cooling fins. you can see all the dirt on the paper towels underneith. also i have added thermal compound between the fins and the cylinder. that should help quite a bit to give those fins a chance to do there job.
here is the piston assembly. note that the flywheel is rusty even though this pump is only 4 monthes old
here is the uncleaned cylinder head to give you an idea of the amount of crug i found inside. either the air filter isnt very good or maybe this is bits of flash that have come of the Chinese parts. the pump is only 4ish monthes old.