Tappet Question

[Aphrael]

I am in the process of assembling my first Lister from a "parts kit".  The only discrepancy I have found in this 12/2 engine so far is that the tappets would not rotate freely because of being gummed up with paint, dirt and rust.  I have them rotating nicely now, but I am puzzled by George's advice on polishing tappet faces.  When I tried to polish the faces on a flat surface, I found that the faces on these brand new tappets are not exactly flat, but are ever-so-slightly concave, as I could only polish a ring on the outer circumference.  But a learn-ed friend of mine says that most flat tappets are not actually flat, but rather are ground with a 60-inch radius convex face, and showed me a reference on the web that says same.  Concave, flat, convex?  Can anyone tell me the correct face geometry for a Lister tappet?   

[mobile_bob]

a properly designed flat tappet or mushroom tappet should be slightly convexed
if you continue to try and hand polish it down on something like a wetstone or oil stone
working it down in a figure 8 pattern, turning it a quarter turn at a time you will find that you will
generate a convex surface on the face.

trying to get it perfectly flat is not what you want and thankfully very difficult to do by hand anyway.

the convexed surface is complimented by the lobe of the cam which is slightly higher on the outer contact area
than it is where it contact the lifter toward the center of the lifter

the two work together to assure rotation of the lifter, in a properly designed setup

all this is of course predecated on haveing a lifter guide that is plumb or perpendicular to the cam centerline

you can check for convex by placeing the flat surface of the lifter across the barrel side of the other lifter, you should feel a bit of rocking
that is evidence of some convexity.

hope this helps

bob g