The rotary valve has no correlation to compression, it is only a crankcase gate to prevent reversion out the carburetor to assure the fuel charge goes into the crankcase and when the piston drops it forces the fuel air mix into the intake port in the cylinder.

The usual cause of no compression on a new rebuild is that the piston ring gaps are aligned with either the intake or exhaust ports, or with themselves. Sometimes the wrong sized piston is used, especially if a cylinder has been rebuilt or rebored.

 

Hey Travis,
New here myself and very interested in your 100. Never worked on a rotary valved engine, only read about them.
I can tell you, you may save yourself alot of chasing down problems by biting the bullet and just going through the whole engine.
That was the only way I could think of to absolutely Know what I had in the engine.
The last few "Bikes in a Box" I brought home I got a service manual and just went through the whole Mary Ann.

The first thing I thought of would have been the Intake also, since there are no reeds I would've thought the timing on the port windows was amuck.
Thanks RW for the insight.
I'd like to know what you find Travis as this is interesting.
Rob\o/

 

Rob,

Thanks for the tip. My plan is to re do the top end and double check all my clearance's and make sure my rings are correct. If still no compression I am going to head to the rotary valve and make sure it is still in tact and functioning properly. I did buy a service manual and I am planning on doing just as you say and going through all the major components one at a time.

Many Thanks.

 

As RCW says compression is down entirely to the piston and rings being the correct sizes and clearances. In two strokes the rings are 'pegged', they have to be to stop them turning and 'snagging' in the transfer ports. The other aspect with two strokes is that the compression ratio is much less than with a four-stroke, usually about 7 to 1 as it won't start to seal until the piston has passed above the ports so if you're used to kicking over a 4 stroke a two stroke will seem to give you little resistance by comparison.

 

Removed right crankcase cover. Hope to get into the valve next week when I have some time. Looking through the intake I can see the Rotary valve spin and it looks like it has some grooves in it and a fair amount of oil on it. My mechanic bud and I speculate that that valve is just not tight and flush as it should be, allowing compression to leak by on the pistons up stroke. With the spark plug in you can feel compression build and then a noticeable burst of air comes out of the intake. So the plan now is to inspect the valve, replace and put it all back together and see what happens. The top end seems good. Good suction on the way down from the top. This rotary engine is really fascinating to work on, never done it before and I am enjoying it. Thanks for all your tips and help

 

I did buy a service manual and I am planning on going through all the major components one at a time.

I see this is not your first BBQ Travis, it's tough to figure out how much experience a guy has in just a few posts and not sound like a bucket head... (well, you know)

I have to find my clymer two stroke old school book and see if your ke100 is in there.
If only to be able to talk about the project and not sound like a total newb. Thanks for sharing. Best of luck!
Tuck\o/

 

I am trying to go slow and get everything in order. I really like this old bike and hope to get in great order. I will keep you guys posted on how it goes.

 

Finally got into the valve. After removing the valve cover and valve it appears the rotary valve has alot of spiraling in the metal and the it also appears to be out of shape on the edge where it opens allowing for fuel intake. I ordered some new parts and hopefully I can get that valve seating flush against the face of the cover. I think I am on to the problem and hopefully I can get her going. I will keep you updated

 

Ahh,
Thanks for the update Travis.

the rotary valve has alot of spiraling in the metal

What does it look like caused the valve to get out of alignment and grooved? Foreign object ? And if you don't mind what keeps the rotary disk in place.
Updated Ohh I see... I wish I'd thought of pulling up the diagram earlier!:shock:
Doohhh!

Rob \o/