Greg---Your reply is nicely written. I guess it's because I have never
experienced "soft lifters or worn cam lobes" that I found it unusual for
the subject to be of concern. I've taken no special care to see that any
break-in time period was followed. If the engine needed attention soon
after start up, I would shut it down to do what was required, and start
it back up. Sometimes hours later. I guess I've been lucky! I'll have
to give it more thought as to where the oil goes when it leaves the
rocker shaft. (I know the bore for the followers are snug)
I agree that if the nose of the cam lobes wear it would not show up when
the valves are closed. However, any significant wear at the followers
should cause the lash to grow at these stations.
So far, so good after about 3,000 miles on the Z-19.
Thanks for your thoughts, here.
Dick
E-mail message
Greg wrote
10:33pm (PDT+3) To: tr6taylor@webtv.net (Sally or Dick Taylor) Re: Soft
Lifters
Dick,
I am certainly no metallurgist, but I do work with plastic injection
molds and see a similar situation where tool steel is damaged as sliding
parts gall from wear, misalignment and/or lack of lubrication. Once it
starts both mating surfaces are damaged as anything less than absolutely
smooth surfaces is death to metal. It may be because the oil does not
stay on the rubbing surface as a protective film but instead falls into
the nooks and crannies of scored and pitted metal, allowing metal to
metal contact without the oil film protection. Another example is what
happens to a brake disc when the pad is allowed to wear to the metal
backing. Both surfaces get chewed up. When I say "soft" it's not that
the lifter is soft as lead, just less than the minimum Rockwell "C"
hardness, which I believe is 55. I guess this is the hardness that can
resist the heat and pressure in the particular application with adequate
lubrication.
Smearing assembly lube on the cam lobes and bearing faces during
assembly is all you can really do on a fresh engine until oil circulates
on that first start. There really is no place for oil to drip down on
the cam from the head to any degree. The lifter bores are effectively
blocked by the lifters as the fit is pretty tight. On TR sixes normal
camshaft lubrication comes from oil thrown off from the crankshaft and
rods, maybe squirting out from the cam journals too, but this does not
really become adequate until 1500 RPM, hence the need to get the revs to
1500 on a new engine. Those first few moments will let the lifters bed
with the cam lobes. The assembly lube simply provides protection until
this occurs.
Valve lash exists at valve closed, or relaxed, position. Valve open is
when the pushrod is actuated by the cam which in turn pushes on the
rocker arm pushing the valve stem down (open). The only measurement I
can think of that would reveal cam/lifter wear would be fully compressed
height of the spring, as a worn lobe will not lift the pushrod as far as
it should which will then affect the degree of valve lift. While there
may be some wear at the cam lobe "closed" position which is the lowest
point of the lobe, the real wear occurs at the highest point of the lobe
due to stresses of pressure and heat. Hope this expanation makes sense.
I really liked the Z-19 grind. I definitely saw a difference, especially
in 3rd gear, and is a good profile when little else is done except maybe
kick up the compression a bit. I had my head cut so compression was
about 9.3:1 with this cam. I've gotten a bit jaded though, so I decided
to go to a hotter cam and 9.9:1 compression along with the other
requisite engine modifications.
Greg
"A little more power is never enough" Caesar
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