REFLECTOR: Setting Valve Clearance

[HYTEC45 at aol.com]

In a message dated 4/24/2009 10:03:23 AM Pacific Daylight Time,  
lwcoen at hotmail.com writes:

Your answer on lifter leak down is incorrect.  If hydraulic lifters  
couldn't bleed down they wouldn't work.  To quote the Franklin Rebuild  Manual, 
"Leak-down rate is meant the rate at which oil escapes between the  cylinder 
and plunger of the hydraulic unit."
The English in the quote is a function of the translation from Polish but  
the meaning is clear. The answer to the question is yes with a caveat.   
When the valve closes, the spring on the plunger will pump the lifter back  up. 
 This would require you to maintain pressure on the pushrod end of  the 
rocker to prevent this from happening as you rotated the engine back to  top 
dead center.  Hydraulic lifters function are to compensate for  dimensional 
changes that take place due to heating and cooling and therefore  must be able 
to adjust in both directions.
 



While this valve 101 should be known by any A&P including me, the  question 
was in response to reassembling cylinders on an engine.  At this  point, I 
read (could have been wrong) he wants to put the valve train back  together. 
 Unless this is more than just a cylinder replacement and the  lifters were 
removed, they should have already been cleaned, lubed, tested, then  
deflated by unseating the ball before reinstallation in the case.  In this  case, 
there would not be and issue with clearance to reassemble the train.   If 
not, the lifters will have dirty oil in them from service, so the leak  down 
rate means nothing.  In reality, you yank the lifter, deflate, slide  back in 
insert pushrod tube cover, pushrod, valve and easly compress to assemble  
all at TDC.  The man just asked how to set a watch, not how a watch  works.
TEC
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