I've read quite a bit about this stuff. I'm not sure I understood
everything about contact stress patches, etc. The bottom line seemed to
be that the lowest contact stress occurs when the cam has no taper and
the lifter is dead flat, and everything lines up perfectly. The worst
case scenario is when the contact occurs on the edge of the lifter.
Apparently, they discovered somewhere back about 1940 that in practice
you can't get perfect alignment, so if you make everything flat, you'll
probably end up with contact on the edge. For one thing, you'll get
some misalignment because there is clearance between the lifter and the
lifter bore, so the lifter can tilt slightly. This is when they came up
with the idea to put a slight crown on the lifter. I'm talking about a
50 to 100 inch radius of a sphere, which gives something like 0.002
inches. This very slight radius on the lifter surface helps to
compensate for any misalignment, and results in much less stress than
contact on the edge.
I should add that Triumph apparently did not subscribe to this idea for
the TR3/4 (not sure about later models), because they used flat
lifters. Most of the after market lifters have a crown. There is no
reason not to put a slight crown on a reconditioned OEM lifter. Real
problems seem to occur when there is a convex surface on the lifter.
That is why reusing old lifters is a no-no.
I tried to contact the guy that did the ceramic lifters - phone
disconnected. We might as well quit talking about them.
Larry
Bill Babcock wrote:
> I was being imprecise saying that a radius isn't proper--most flat
> tappets have some spherical crown, but it's a very large radius, and
> the best lifters I've found by far for wear on the cam and the lifters
> at high RPM (6800 shift point) are the ceramic ones I have in Peyote's
> two-year engine, and they have no crown at all--at least none i can
> find with a surface plate.
>
> Unfortunately I can't find any more, and I hear they can suddenly
> break, but my experience is an engine run hard for two years,
> including the fourteen events of the All Aluminum tour, with
> absolutely NO wear on the cam and not a mark on the lifters.
>
> I've seen tappets that have been reconditioned with radius that more
> like what you see with hydraulic tappets. I think that's a really bad
> idea. Given my druthers I'd rather have the completely flat.
>
> On Mar 15, 2008, at 10:20 AM, John McCue wrote:
>
>
>> That's not what the guys at Huffaker or APT say. John
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