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Old 10-01-2008 | 12:06 AM
  #22  
chashint
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From: Rowlett, TX
Default RE: thunder tiger .91 4 stroke issues


ORIGINAL: DarZeelon

ORIGINAL: chashint
Here is a link to the manual. http://www.thundertiger4u.com/pdf/f_91s.pdf Page 9 has the valve adjustment information.
Charlie,
There is one thing on page 9 I cannot subscribe to and this goes for all four-stroke engines... It reads to turn the prop to a location where "both lifters/followers are 'somewhere' on the cam's base-circle"... The machining accuracy of the cams may be such, that the base-circle is not perfectly concentric with the camshaft... Each valve must be regarded as an individual adjustment item; and that means it must be adjusted 'alone', with the very middle of its cam's base-circle on its lifter/follower, without any regard to the position of any other valve... This is very easy to find... Select one valve. Look at the rocker of that valve and rotate the prop find its 'point of maximum lift'. From there, rotate the prop exactly one complete turn, 360º (this will rotate the camshaft exactly 180º; one-half of a turn, to the point opposite the cam's peak) and adjust that valve's lash only. Repeat this procedure for the other valve. Also the adjustment should target the minimum value (to maximize total lift and duration)... The go/no-go procedure described is just too crude and could result in a power loss and more valve-train noise/wear.
Apparently the instructions in the manual were adequate, he adjusted the valves and is very satisified with the engine's performance.
While I understand that some people are not satisified with "good enough" I have not had any issues with the go / no-go method. In fact I am a huge believer in "if it ain't broke don't fix it" so I never even check the valves unless one of the engines starts to run poorly. At that time I will work on it, otherwise it is fly em and oil them if they are going to sit for a while. All of my engines run great and I hardly ever have to fiddle with one of them so I am a happy camper.