Differences

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--- techtalk:ih:engmech04 [2019/06/14 19:48]
hippysmack [Sub-Documents]
+++ techtalk:ih:engmech04 [2021/11/05 20:23]
hippysmack [Pushrod Tubes]
@@ Line 43: / Line 43: @@
 |  Rocker arms on a 69 XLH ((photos by austinshovel of the XLFORUM http://xlforum.net/forums/showthread.php?t=1913766&highlight=rocker+arm+bushings))  ||
 |{{:techtalk:ih:engmech:ih_rocker_arms_1_by_austinshovel.jpg?direct&300|}}|{{:techtalk:ih:engmech:ih_rocker_arms_2_by_austinshovel.jpg?direct&300|}}|
+====== Pushrod Tubes ======
+**Pushrod tube orientation by Dr Dick** ((http://xlforum.net/forums/showpost.php?p=3855693&postcount=11)) \\
+Pushrod tubes seal in 3 places. 2 of those, the upper and lower corks, seal on their flat faces. \\
+Now think about the center cork. What does it seal? \\
+The only joint at center position is the telescope joint. So seal needs to be on outside of the upper tube where it meets the inside of the lower tube. \\
+With the center cork being spring loaded into the flare on the lower tube; \\
+The cork gets squeezed into the flare and 'chinese handcuffs' to the outside of the upper. \\
+Not only does this seal the telescope, it tends to reduce the OD of the center cork as it squeezes around the inner tube. \\
+So what? \\
+Well, if you flip the lower tube so the flat is at center cork, the spring still squeezes the cork. \\
+As the cork gets pushed thinner, it gets smaller on it's ID sealing just as it needs to. \\
+But it also gets bigger on it's OD (sealing to the inside of the spring cup piece. \\
+And trapping rain/wash water inside the cup above the cork (rusting the spring until it snaps). \\
+Meanwhile at the bottom, the cork is getting squeezed into the flare. \\
+Nothing is there for the cork to seal to until the cork gets small enough in diameter. \\
+And fat enough in thickness that the tappet starts to be the thing it wants to seal to. \\
+On a bike with stock or even .436 lift cams, this just creates a leak at bottom cork after enough miles. \\
+But if you happen to have a bike with more lift-- say .475 for instance, then the top of tappet may go above the cork seat surface of guide at full lift. \\
+Now that extra tappet-cork kissing contest works the cork into the tube flare real fast. \\
+Maybe fast enough that it constricts oil flow before you get home and notice the leak. \\
+And the ensuing tappet/guide wear from letting the lube escape from the tube each time the tappets hits the cork. \\
+(lifting it off the guide and letting lube out to the wind) \\
+Look at the shape of the rocker box seat. Its reverse flare to squeeze the cork tight to the OD of the bore in the box. \\
+So it don't fall down every time you open the tube. \\
+You late model guys who have the full O-ring setup instead of corks, some of you may suffer from crappy top and bottom O-ring life. \\
+When you take the bad O-rings out, they are smashed flat. To get rid of that, try putting corks in the center position only. \\
+It's the center O-ring getting tighter an tighter that kills the end of the O-ring by not letting the tube to telescope shorter during hot cold cycle. \\
+That's why the center O-rings are always jammed. \\
+Periodic maintenance is one of the hallmarks of a devoted owner. \\
+When possible, while building your ride working to extend the period between these required attentions may keep money in your pocket and your bike on the road. \\
 \\
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