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
CD6250L
----- Original Message -----
From: "Sally or Dick Taylor" <tr6taylor@webtv.net>
To: "Gregory Dito" <g.dito@worldnet.att.net>
Cc: "michael lunsford" <mblunsfordsr@yahoo.com>; <6pack@autox.team.net>
Sent: Friday, May 30, 2003 9:28 PM
Subject: Re: Soft Lifters
> Hi, Greg---I also have the relatively new Z-19 Isky cam. Pains were
> taken to pre-lube the cam and followers prior to start-up, yada,yada, as
> always, tho I still can't follow the reasoning why soft lifters should
> play hell on the lobes. Seems to me soft lifters would be the
> sacrificial metal here, and leave the lobes whole. Any metallurgical
> reason for this?
> Also, I would think that as certain parts of the cam drive were going
> away, the lash would increase more on those stations.
>
> On the same subject, I have always poured motor oil down the cam
> follower (pushrod) bores prior to a fresh parts startup. Some of this
> oil has to find its way down on to the cam lobes, to assist initial
> run-in. I would also think normal run-off of rocker shaft oil would
> continue to drain into these valleys, to aid the splash system.
>
> Dick
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