Re: valve clearance hot vs cold

Posted by Janicholson on July 31, 2007 at 22:39:35 from (71.87.39.51):

In Reply to: valve clearance hot vs cold posted by sgtbull on July 31, 2007 at 19:49:02:

Between the base circle and the lobe on a solid lifter,or roller lifter cam, there is a ramp. This ramp is not really visible as a feature to look at with ones Eye, it is a design feature that takes up the clearance built into the valve train design. It is the height of the valve train clearance at running engine temperature condition of the engine. When the valves are set to the correct spec., this ramp top will be just at the contact patch of the lifter when the valve is spposed to start opening. It will have only provided a slow reduction in slac in the system keeping noise, and impact related wear to a minimum. If too loose on adjustment, the ramp is not able to eliminate the slack, and the valve opens late (as well as the ticking sound of a loose adjustment. If clearance is too tight, the valve starts opening (just a crack) too soon, allowing hot gasses to whistle past the seat and face Providing erosive high temperature damage to seat and face. Thus it is reasonable to be fussy on the adjustment, and if specified as hot, the engine should be at full operating temp then the VC removed and adjustment made as fast as is reasonable to do it. Engineers and cam designers are the ones deciding on the cold adjustment by setting multiple engines hot, then letting them cool to ambient and measuring the actual clearance "cold" then averaging multiple readings to give a spec. A Crane Cam designer discussed this with a group of us in the design department of Crane in 1969, JimN

Replies:

• Re: WOO THERE Tom Windsor 23:20:29 07/31/07 (0)

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