Crankcase Check Valves
offered by Crabbysteve & Darth

Crankcase check valves (scavenging pumps) were added to H series engines for 1974 and later models.  The purpose was to reduce emissions.


Here are some pictures of where they are located in the crankshaft area.
As you can see there is a hole in the bottom off the crank flywheel area.
The oil travels through the check valve and up to the hole located between the crank seal/bearing on the left side of each cylinder.
All this is doing is throwing whatever oil seeps to the bottom into the left crank bearing to be burned again.

Further explanation is here pg138.

Early H1                                                                      Late H1



Since hydro-lock is a possibility ... I was thinking they could be used like case drains.

Discard the center section, make a blanking gasket, some short bolts and a lock washer and wha-lah !!

In the spring, or after long periods of sitting, remove the plate and check/drain the case ...

As you can see, the case has large holes drilled into it. The center section has small holes. That's why I was thinking that the center section should be removed. The oil (if any) wouldn't drain through these tiny holes in the center section very well ... if at all.

If you wanted to keep the "original appearance", you could just drill out the center section to match the the other holes I guess.

The small screws hold the top plate to the center section and the large screws hold the entire assembly to the case.

You can also see how the "case pressure" directly affects the reed, since that is the hole it is "valving".

If you take these off and rebuild them, you need to be aware of the orientation. You can put them back on 180 degrees out. Then the reed is covering the bearing hole ... not the case hole. It all lines up either way you install them. BUT ... one way it works, the other way it won't.

I have the pieces oriented in the pic the way they should be ... and the entire case is "upside down" in the pic.

I don't know about you guys ... but  I now know more about these things than I ever wanted to know ... LMFAO   ... but it's all good.

Actually, I kinda wish I had them on my bike ... just for the case drain feature.

IF a person was going to use these as drain valves ... then I would think the drilling would be in order.

IF they were going to be used as intended by Kaw ... leave all the pieces "as they are" and obtain the correct gaskets (unobtainable).

If a guy wanted to, he could make an O-ringed drain plug that would just go through the case hole in the thin cover plate. And drill the center section to match. Then all that would be necessary would be to remove that plug ... much like draining the tranny.