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Re: Tappet talk

Subject: Re: Tappet talk
Date: Fri, 6 Jan 2006 15:48:52 EST
In a message dated 1/6/2006 3:02:04 PM Eastern Standard Time,  

I can't  visualize how doming would help
rotation unless it was moving the contact  patch off center in a cam/lifter
pair where the cam lobe was centered over  the lifter. 

The cam lobe is indeed off center from the tappet centerline.
FWIW I have info direct from Piper (some years ago) re an inquiry I made,  at 
the time they ground their lobes in at 5 minutes, don't have spec for their  
tappet radius. They generally show up as not quite perfectly flat when  
checked with a straightedge, it's a VERY SLIGHT"dome". 
I agree that there are many different opinions on these things but we also  
have have to realize that we're dealing with the basic Triumph pushrod engine,  
modern OHC bucket & roller types are obviously different.

"I have about 30 lifters. All domed ones have pitting near the center  of
rotation. The perfect flat ones didn't fail so far and have a smooth  surface.
Everytime I install lifters I inspect the surface NOT to be  domed."

I cant't argue with someone elses good results. I too sometimes have the  
pitting problems as you describe. Assuming that the tappet is hard  & turning 
properly, I've attributed that to an excess load issue &  lube breakdown. The 
acceleration rate, weights, & spring pressures,  etc are all variables here 
of course.
Now, if Uncle Jack follows this thread, we might be in for another  survey...
Thanks for the feedback,
(not a cam designer)

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