I goofed and sent this to Randall instead of the List. Need more coffee.
Jim
>At 12:33 11/6/2004, you wrote:
>> > Whoops. I guess I'm a bit too literal. When you say "lost a lobe," I
>> > assumed that the specs on the lobe itself ground beyond
>> > tolerance. Couldn't
>> > figure the talk on a soft lifter, since to overly wear a cam lobe
>> > would have
>> > to mean a tight, hard lifter.
>>
>>Not true at all. I don't know the exact process involved, whether it's just
>>the soft lifter losing it's finish and grinding away the cam as Irv says, or
>>if there is actually galling (a kind of microscopic spot welding) involved,
>>but I do know that soft lifters spell death for a cam lobe.
>
>Randall is correct (no surprise there). In a previous life I was a
>mechanical engineer who designed slip rings (rotating sliding contacts to
>transmit electrical signals and power) for the aerospace industry (I'm
>proud to say one of my devices was on the first Shuttle decades ago, but
>that's a different thread). Anyway, the process by which soft lifters
>wear hard cam lobes is called back transfer. If the film strength of the
>lubricant is exceeded, even for an instant, the harder material generates
>wear particles which then back-transfer to and become embedded in the
>softer material. The softer material then becomes an abrasive (think
>Craytex stick) and the irreversible process of abrasion of the harder
>surface commences. It's not intuitive, but that's the mechanism at work.
>
></tribology lesson> :-)
>
>BTW, when I had my cam reground by Isky about 4 years ago, I sent my newly
>purchased lifters to them to be hardness tested; seven of the eight
>passed. They wanted RC 53 or better.
>
>hth
>
>Jim
>
>--
>Jim
>jhassall@blacksburg.net
>Blacksburg VA
>'63 TR4 in autox preparation, 90% finished, 90% to go
--
Jim
jhassall@blacksburg.net
Blacksburg VA
'63 TR4 in autox preparation, 90% finished, 90% to go
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