gas mileage/setting valves
Last week I adjusted the valves and did a throttle sync and was very deliberate and careful about setting the valves a little looser than my last bout with the valves. My bike's engine has never run better for me...very smooth, good low end torque, and not even a hint of surging. The mileage is down about 4 miles per gallon and I was wondering if the more open valves would be inclined to do that. (by the way, my bike is a 1994 R1100RS, now with just under 50,000 miles on it)
(I've just finished the major service myself)
When setting valves, I use the "look" method.
Generally speaking, there isn't a gasoline engine made that is sensitive to valve adjustment +/- 0.001". In my experience with gasoline engines, the "feel" of feeler gauge is deceptive. The springs are too light and the contact area is very narrow. What's tight to some is loose to others.
The only accurate method of determining proper valve clearance that I know of is by using the timing/overlap method. It requires knowing the exact position of the piston and crankshaft angle. It's very time and tool intensive and takes practice. On some engines that I work on routinely, it takes me over an hour to set the valves on any individual cylinder.
For these little girls, I put my feeler gauge in, tighten the adjuster until I can see the spring compress a bit, back it off, try again with less force. If I can slide the feeler gauge out without deflection from the spring, I'm damn close to spec. I know a guy that sets his torque wrench to 4"/lbs and calls it a day.
If you want to really get into a mess, you need to make sure that the valve train is in good condition. That means you can't have case hardening drop outs or dished out valve stems or push rod tubes that are coming apart. Throw a flat lifter roller in, the mess get's bad, fast.
A good valve set is an art. Art takes practice.
More exact measure of clearance?
I wonder if an electronic gizmo has been invented to measure the pressure in the gap. Something like a feeler gauge but with a digital readout. It seems this might lead to more exact & even setting of valve lash.
Background: in the 3 years and 50K mi I have owned the bike I have set valves & throttle bodies many times, but only one time was magical: the bike ran super smooth with good power at takeoff and almost no surging for 4-5 months. I have never been able to completely duplicate the magic tuneup!
My source has been ADVrider's Hall of Wisdom, Valve Adjustment for Dummies.