UMS 7-90 cc User Manual page 12

Radial Valve Adjustment Guidelines
1. Place the engine in a position (on or off your airplane)that allows you easy access
to the valves on all the cylinders.
2. Remove the spark plugs from all the cylinders. It is much easier to determine Top Dead
Center (TDC) without the compression caused by installed spark plugs.
3. Attach a propeller or other turning device (such as a short block of wood with the
appropriate hole for the crankshaft) to the crankshaft and tighten it so you can easily
rotate the crankshaft throughout this process.
4. Start with the number 1 cylinder (this should be the upright cylinder above the
Tomahawk logo).
a. Rotate the crankshaft counter-clockwise and observe the pushrod movement.
b. Note when you see the exhaust and then the intake pushrod move up to open
the valves. This will occur during one rotation of the crankshaft.
c. When the piston reaches the top of the cylinder during the next rotation,
you are at the TDC of the compression/ring stroke.
d. Position the piston at TDC of the compression/ring stroke. It is helpful to place
a short piece of wooden dowel. (Don't use steel, as you can mar the inner surface
of the cylinder.)
5. Use a feeler gauge to check the valve lash between the rocker arm and the top
of the valve.
a. We recommend setting the valve lash as close to 0.1mm as possible. If the valve lash
is between 0.05 and 0.08mm you do not need to adjust the valve lash.
The settings for the intake and exhaust valves are the same.
b. If adjustment is needed, adjust the valves by loosening the locking nut and adjusting
the screw until you can just feel the drag of the 0.05 feeler gauge as you pull
it between the valve and rocker arm.
c. Tighten the locking nut and recheck the valve clearance. Sometimes when tightening
the nut the adjustment will change slightly.
6. Because the cam gear of our engines is a shared cam gear with all the cylinders and
rotates at a 1:6 & 1:8 ratio, there are actually 6 & 8 different positions on the cam gear
that need to be checked. Repeat step 6 & 8 above four more times to check each of
these positions, rotating the crankshaft 6 & 8 full revolutions between each check. If you
nd that the valve lash is smaller, then readjust that valve. If it is greater, do not readjust
the valve. A little loose is safer than too tight. (Note : 1:8 for 9-115cc)
7. Now move onto the next cylinder in a counter-clockwise direction and repeat steps
4 through 5. Do this for all 7 & 9 cylinders.
Congratulations. You have now completed the valve adjustment process. This maintenance
should not be required again for another 10 hours of running time.
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