Cmep-ol piston head space

Hate to be a bother…
Anyone know the specs on piston head space/valve body clearance for the cmep-ol?
Haven’t been able to find any literature. I’m at around 8-hundreths of an inch.


It just needs to be enough clearance so it doesn’t contact when it warms up. Haven’t seen factory documentation for an actual number nor is there really any adjustment other than stacking on additional sealing rings at the cylinder base. Both the valves are spring loaded so they won’t contact piston top unless the pump aspirates some hash or the spring or valve breaks

Got it. Use the ol eyeball method.
I was wishing in one hand for a secret volume of exchange for maximum suck and blow

Unfortunately there isn’t a spec for proper headspace on the CMEP-OL. There are two schools of thought though that we have found from talking with customers.

  1. Space the head as close to the piston as possible without contacting. The thought being, this may offer the best performance, but no room for error if a little fluid gets sucked through or pressure spikes and could cause the crank bearings to fail prematurely.

  2. Give some extra space between the head and the piston. This creates a small buffer for minor amounts of liquid or pressure spikes, and hopefully not damage the crank bearings, but may run a slight bit lower performance.

We try for the happy medium or a bit on the closer side, as we haven’t seen a huge difference in life span of the bearings. And the performance difference, we don’t think, is much of a difference either. We usually start out with 2 thick paper gaskets and 1 thin gasket per cylinder and check for contact. If it touches or its too close to tell, we add a thick gasket and recheck.

.08 is plenty of head space imho. That’s over 1/16". You can be down around 1/32", or .03125 and you’re fine.

I agree

Check out our High-Flow Kit. Getting rid of some of the worst restrictions on the CMEP-OL.
Link: EGI High-Flow Kit

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Reminds me of the old shadetree stroked out aircooled dirtbikes that once they heated up the piston started smacking the head! PINGPINGPINGPINGPING

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Have you guys tested your high flow kit head to head with an unmodified CMEP to see how recovery speed compares? I know its a bigger pipe and certainly that won’t hurt recovery speed, but it seems to me that there’s a few other places on the CMEPs that could be optimized with straight or swept elbows instead of hard 90 elbows with sharp turns that could also dramatically improve flow.


how does the compression and cylinder volume on those compare to say the Corken?

throw a 10 or 20HP surplus atex rated centrifuge motor (or Im I the only one plagued by those?) in where the rear wheel was and “ride to recovery” while playing MX vs ATV

:rofl: :joy: :rofl:

(don’t forget to remove the spark plugs :shushing_face: )

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Yes we have tested it. Actually the kit was installed on a few customers pumps that ran multiple pumps in their systems. The flow it self did improve, we know this from overall recovery time dropping for all the testers. What first surprised us was the lower output temps. This was simply tested with a laser temp gun on the output line. The overall temp on the pump body itself also lowered.

Someone could change the routing of the hard lines some and may get a slight difference, the real restrictions are the factory valves and the heads themselves. I’ve been playing with the heads, machining out the valve orifices, and fitting orifices, to open them up. I’ve even adapted the larger exhaust valve for the 710 into one of these heads. And it is possible to open them up to the point that performance gets no better, they are just simply maxed out. The idea is to increase flow to maximum potential while also lowering the cylinder compression to relieve stress felt by the crank bearings.


I was just talking with my crew about how interesting it is that recovery pumps are just 2-stroke engines without the spark!

Local man dies after trying to speed up bho recovery by sending his tane through his dirtbike. Sources say he forgot to remove the spark plug. More on this story at 8…


Another way to get more performance from a CMEP-OL, add a second pump head. We are currently doing this in house only. We are gathering all parts needed to have this as an add-on kit, diy. It’s for Gen 3 models, and all fits inside the original frame and shell.


Very nice!