Problem with CMEP-OL

I’ve just installed 2 new cylinder heads on our CMEP-OL. It ran fine for a few hours then died. When i turn it on, the fan moves a quick inch and it doesn’t turn over.

Has anyone experienced this? I’ll try a full rebuild if necessary.

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Pull the fan cover and see how hard it is to turn. Did you aspirate extract into the pump? When you rebuilt the top end did you do any bearings on the bottom end? IMO the cmep needs the bottom end redone about twice as often as the top because of their crapshoot design that washes grease out of the crankcase bearings and causes them to fail


Thank you. I will look in to your suggestion ASAP.

Did you find anything out? The rec lab I work has a cmep and it just did the same thing this morning.

They use filters inline and at the pump so I doubt anything got into the pump per se. but who knows…

If nothing was aspirated the bottom end is likely toast. Only way to be sure is pull the cylinder jugs and check if there’s anything sticky in there, you can also check how much play the rods have and see if either one is seized to the crank while the cylinders are off. Alternatively, pull the crankcase cover off of either side and look for pieces sitting in the bottom of the crankcase. 9/10 times there’s whats left of the seals and a bunch of grease, maybe even some balls out of the bearings laying at the low point.

Krytox vacc grease is a high performance bearing grease. Pop the seal off carefully re pack night and day better than the shell #2 grease that comes in them. If done correctly…

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Also then you replace the topend it is best to place the cylinder on then place the piston on with the new paper centered as well as possible then put the screw in and tighten piston down to the connecting rod to seat the new paper. Much metter than the way eco green reccomends is to install the piston then roll the cylinder on but a haskell piston must be installed from the top of the barrrel downward. Makes since for best seat.

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When you say bottom end toast is that repairable? What would cause this? It’s never been abused with a total of maybe 50 hours run time.

As long as the bearings didn’t spin on the crank and wreck it, yes it is repairable (it’s repairable if they did too but it’ll take someone with a welder and lathe or shaft grinder to do so). Cause would probably be that they have an incredibly crappy design that doesn’t vent the crankcase, causing solvent to get into the bearing grease when it’s under positive pressure and then when the pump gets into vacuum the solvent-laden grease expands, blows off the bearing seals and throws it all over the crankcase, lack of lubrication then destroys the rod bearings.

If you’re near the Denver area I’ve rebuilt a couple of CMEPs and can show you how its done.

I wish. It’s located in a 502 in WA state.

Thanks for the information I just got the go ahead to tear it apart. Probably start that next week once again thanks for the information I’ll post here once I do the tear down.

I own CMEP Shop. I am a factory authorized repair and parts facility in California. I have a service where you send me your compressor and i rebuild it and send back in 48 hours. I have every part available. I take care of the shipping as well so you get a discount of regular UPS insured prices.

putting krytox in a bearing not designed for high temperatures will only extend the life a little. You must have a high temperature bearing, that has high temp grease.

The biggest problem with these pumps is people do not have them set up and run liquid through the pump. Liquid is not compressible. When the compressor attempts to compress the liquid, you get “blow by” AKA liquid into the case and remove the grease form the internal bearing. This can also damage the valves and in bad situations, the gauges.

I recommend having the pump elevated off the ground to be the highest point in the system. You also need to have your molecular sieve vertically mounted, bottom fill. The top of the sieve should be at least a foot below the pump. You coil in the down flow should also have it’s ins/outs at least a foot below the pump. To get my repair warranty, my customers must follow these instructions. This works.

contact me if you need parts or want to set up a repair. Rob at the CMEP Shop


Hello buddy…quick question. I heard if you elevate pumps higher that collection it will recover faster??

It will work more efficiently and save your pump from excessive repair. If it’s on the ground the vapor being recovered can condense in the crankcase and wash out the grease and or ruin the seals destroying the pump much faster. @Jaybird949

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It wont recover faster, but as 710enigmatis says, it will prolong the life of your pump.

Remove the built in condenser/radiator and you will get over 15% faster. Also replace your piston seals every 150 hours. Finally keep the pump cool by putting a fan or even better AC unit blowing on it. Cold pumps work better.

Other rules for longevity are keep the pumps temps below 100ºF. Max operating temp is 104º, posted on sticker on top of pump. I recommend 80-85º. You Mol Sieve should be vertically placed. Dry your sieve beads out daily. Your mol sieve and external coil should be placed 1’ below the inputs of your pump.

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I live in co and looking to get my pumps rebuilt. Can someone email me some solid refs. Thanks.


@RobSpear is your man.

i can give you some tips. pm me.

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@RobSpear How much for a full rebuild?

640 without new cylinders, 740 with new cylinders. All new bearings, seals, o-rings, internal assembly hardware. + pressure test.

If you are out of my area, I can send you core removal instructions, and arrange shipping through UPS insured for a discount, and send you a tag.

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Hey I’m located near Denver and have 2 pumps that need repaired. Any chance we can schedule a time to meet?