| Comment: Follower bores in the crankcase are typically never
inspected for wear. If they are inspected they are not suitably inspected
as to the difficulty of measuring run-out and concentricity in the small
cavity. Now this is not necessary an omission; If the followers coming
out of the engine look good then it stands to reason that the bore was
positioning the followers properly. The problem arises in that what happens
when the bore is worn and causing the follower not to operate properly?
The answer is probably not what you would expect.
When the bore wears and the follower is allowed to move from side to
side it causes small chips on the outside edges of the follower face. When
you see these you would think that they occurred when the follower was
dropped on the concrete floor and then installed into the engine. This
is usually not the case. The mis-aligned follower allows the camshaft
lobe to push down on the outside edge of the face causing the edges to
chip away. You can verify the misalignment by a careful examination of
the wear marks on the lifter.
Possible causes:
1. Dropped on edge (doubtful)
2. Camshaft bore worn allowing camshaft to "walk" thereby allowing
camshaft lobe to press against outer edge of follower face. Loading at
edge causes cracks and chips from face
3. Follower bore worn allowing camshaft lobe to press against outer
edge of follower face. Loading at edge causes
cracks and chips from face. (most probable)
4. Nicks on SIDE of follower
Discussion of (2) and (3):
Check the face of the follower for other cracks along the outer edge.
Use a 10X lens and hold the follower so that the light reflects off the
surface. Small cracks should show. You can also Magnaflux the face. If
you see additional cracks in different locations than the chip(s) then
the chip(s) was not caused by a single drop of the follower on the hangar
floor.
Next look for a wear pattern around the outer edge. You should look
carefully with a bench microscope or lens. What you are looking for is
wear around the outer edge than is heavier on one side of the circle than
the other. In other words if the follower face is not contacting the camshaft
lobe at a right angle then the wear is distributed unevenly around the
circumference of the follower face. This indicates a misalignment.
Next, carefully examine the sides of the follower. At the lower portion
(opposite to follower face) of the follower side look for the slightly
darker area where the original machining marks have been worn off. Is this
evenly distributed around the entire circumference or is it only on one
half and not the other. Uneven wear around the circumference indicates
a lifter that is not perpendicular in the bore. Suspect that the follower
bore is worn. If the wear is not even around the lower circumference then
you should examine the upper portion (upper meaning closest to tappet face).
Again look for the slightly darker or polished surface where the manufacturing
machining marks have been worn off. If the follower is not perpendicular
in the bore then the dark area on the top side should be opposite the dark
area on the lower bore.
Discussion of (4)
If the side of the follower is nicked, as might occur if they are all
thrown into a tray during engine overhaul, then the nick creates a raised
area on the side of the follower. This raised area creates the same affect
as a out-of-round follower. The follower does not center in the bore and
thus the camshaft lobe contacts the follower face at the edge.
 If
you're a pilot, you're supposed to tell your gunner or crew when to bail out
--not ask them. Parachute Sense US NAVY 1944
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