RE: UMS Evolution Radial Care and Operation
Todays discussion concerns proper valve adjustment. First in my 30 years of 4 cycle engine flying I have found with complete consistency that valve adjustment is NOT critical. I have numerous times purposefully misadjusted valves and could barley perceive differences. What IS important is adjustment must allow both intake and exhaust valves to close completely or running goes to hell and valves and their seats get damaged on the double. Do not get me wrong I have high expectations of running quality and smooth transition through the throttle range.
Radials excepting the Saitos have a cam ring with multiple lobes to operate the valves. The more lobes the slower the cam ring runs relative to the shaft speed. Take a quiz! A cam ring has 5 lobe pairs.....what is its speed relative to the crank shaft?
OK on to the process; Removing all the glow plugs makes timing much easier so rotation is easy and the pistons can be seen at top dead center. Now start with the top cylinder even though this does not make a difference(you can start with any cylinder). Turn the prop to the point where both rockers are just moving and then one full turn to top dead center. You can see the piston through the glow plug hole. Turn the prop to the pistons highest point. Both rockers should have play. Adjust for correct clearance. You are NOT finished with this adjustment!! Now rotate the prop two full turns clockwise to the exact same position. The rockers might have the same clearance or have greater or lesser clearance. If lesser, readjust to correct. If greater leave alone. Now rotate the prop clockwise two full turns to again the same position. Check the clearance yet again, If lesser readjust if greater leave alone. The point is to never have a valve with too little clearance. A bit more does not hurt. Repeat this process for the remaining cylinders. You see each adjustment position is on a different cam lobe pair. This sounds like horrible tedium but once you get through a couple of cylinders it will go much faster than you thought. I can do the 9-90 in about one half hour. Maybe one glass of wine will help (only one!).