Tearing down an engine of unknown background. The bottom of the lifter is flat as a pancake. Are unused ones convex?
your either lookin at a beat up lifter or a mushroom lifter. A mushroom lifter adds duration by opening sooner as its base rides the ramp sooner.
Yes, but I doubt it is something you can see. The lifter needs to spin. The cam lobes are tapered, and the crown on the lifter bottom induce the lifter to spin. You might be able to see a circular pattern on the bottom of the lifter. If the lifter does not spin, the cam lobe and the lifter bottom will wear.
If you out two lifters bottom to bottom you should see they are not flat. If they sit flat against each other, they're worn out.
If these are from a "NailHead" they were originally flat from the factory. It used the taper on the cam lobe for spinning & the lifter bores ARE NOT at 90* angles.
General rule of thumb is two take two lifters, .... hold the bottom of the lifter in question to the side of the other lifter. If the lifter is convex it is good. Its hard to find a set of old used lifters that are perfectly convex. Larry is correct about the tapered cam lobes though the taper also serves to keep the camshaft pulled to the rear of the block along with the distributor/oil pump drive gear resistance. Larry
If the engine is fairly high mileage you'll probably find the lifter face is concave. Position a thin metal ruler on end across the lifter face and hold it up to a light. You'll see in a hurry what condition it is with all the light getting through. You would think the cam would get chewed up by that but they'd have been run tens of thousands of miles like that and the cam was fine. I guess once they mated with each other the cam survived. Tougher cam back then too. You can really tell you have worn lifters when they are very hard to remove and the only way to get the out is to pull the lifters up as far as they can go, pull the cam, and then tap the lifter out the bottom of the bore. The lifter face is actually wider at the face, shaped like a tiny bell.
Lifters that are difficult to remove are actually caused by oil and dirt that has been coking onto the surface just below the bottom edge of the lifter bore . A good shot of quality carb cleaner spray followed by a shot of lubricating penetrating oil on that area normally assists their removeal, .... though some may be tough and have to be removed as Mike described. I personally have never seen a lifter flared out on the bottom. Larry
Obviously it was only a couple of thousandths because that would be all it takes to keep it from coming out the top of the lifter bore. All the Gumout and cleaning of the base of the lifter would not do it nor would a pair of vice grip pliers on the lifters. You could tell it was "belled" because the lifter would get up into the bore right up to its' face and then stop. At that point it was not the dark coking ring holding up the works. If you think about it once a lifter goes concave it has to start to "push out" around the edge slowly but surely. I would say any lifter that is very hard to get out the top after all the appropriate cleaning is done, as suggested could have some flaring going on. Definitely not saying it was a regular occurrence but that it can happen.
Is that something that changed in later production? The SAE paper on the "New" Buick engine from '53 specifies that the lifters are flat, not convex, the cam lobes are not tapered, and the lifter bores are not offset from the cam lobes. The lifters are not intended to spin. http://papers.sae.org/530248/ The Nailhead is the only OHV V-8 I know of that wasn't designed with features to spin the lifters.
