<VV> Camshafts

[Tony Underwood]

At 01:15 hours 05/29/2006, NicolCS at aol.com wrote:
>Clark sez:
><snip>Craig Nicol says cams are soft when new and harden in use.  WRONG!
>I have the Corvair cam drawings and they are flame hardened or induction
>hardened, ground polished and coated with special compounds to reduce
>friction.
>So in effect they are made hard and slippery and are worn soft in use!
>Clark Hartzel, CPF Curator <unsnip>
>And I (Craig) reply - if this is true, why are failures common on new cams
>but not cams that have gone 25K?  Why won't GM warantee a cam unless 
>there's a
>can of EOS (super protective moly oil suppliment) on the receipt? Why will a
>cam that survives the first 1000 miles go 200,000 miles?  Yes, GM takes great
>pains to harden the surface, but it gets even harder once it's broken in.


If that were the case, the camshafts would never wear out.

The early cam failure usually seen is generally because of improper 
lube upon initial startup combined with incorrect break-in 
speed.    You can't allow the engine to just idle when first started 
following a cam replacement or rebuild, it needs to be run at around 
4000 rpm ort thereabouts as soon as it fires... keep plenty of splash 
oil on everything.

By the way... it's not 1000 miles.   It's more like the first 5 
minutes that matter most.


The cams (the iron ones anyway) DO "get soft" with age once the 
surface hardening is worn off.   The surface is usually induction 
hardened and then phosphate coated... the phosphate coat or 
"Parkerizing" leaves a good surface to hold lube so the lifter faces 
and the cam lobes will wear in smoothly and evenly as the Parkerizing 
wears off.

If you look at a hardened camshaft with a lot of miles on it, you can 
sometimes see the hard areas which contrast with the underlying 
softer iron, from the wearing off of the hardened surface on the toes 
of the lobes and sometimes on the edges of the heels of the lobes.


The trick is to have the two surfaces wear into one another quickly 
without either wearing excessively and thus losing its surface 
hardening.  You'll note that a lot of new lifters have their faces 
phosphate coated as well.   The moly lube sticks to the Parkerizing 
well and the "Parked" surface itself is not extraordinarily hard so 
it wears down fairly quickly, "paving the way" for the two surfaces 
to match up to one another before wearing through the surface 
hardening.    Once they mate up together they usually last as long as 
the engine, or longer.   But if that hardened iron surface wears off, 
the lifter or the lobe usually gets wiped in short order.   A lot 
depends on deep the induction hardening went... and how stiff the 
springs are and how large the valves are (valve train inertia), all 
of which causes wear on lifter faces and cam lobes.


tony..