CAM
SPECS:
Keep
in mind these profile numbers are just for comparing
the cams to each other; every manufacturer and cam
grinder uses different points in the cycle to take the
measurements and they can be listed at almost whatever
they want them to be with the same cam. Some of this
is advertising nonsense; so when looking at cams for
any car; make sure you are comparing apples to apples.
Even Nissan's published specs are sometimes all over
the place. I would think Nissan would be consistent in
their methods and in the cam design but I've seen
multiple specs; especially for the "C" cam. I think
everyone of the old "Comp" catalogs were
different!
Historically
cam specs were advertising figures; like horsepower
that was based on the THEORETICAL amount generated by
the explosion in say 8 cylinders and didn't include
drag from main bearings etc!; or having to move the
crankshaft mass around and around. Engine HP/Torque
means nothing unless it is measured with a chassis
dynamometer with a street exhaust and street air
cleaner system in place.
Such
is the situation with cam measurements. I can look at
you (but not with a straight face) and tell you a
standard "SU" grind has 330 degrees of duration. It
would be "true"; but at what point in the cycle is
this measurement being taken?
Then
my advertising copy would continue; BUT GO WITH THE
SOLEX CAM it has 360 degrees! Again; at what point?
And is that exhaust, intake, both. The figures use in
the 50s and 60s were the GROSSEST of
numbers.
Some
of the more thoughtful cam grinders and engine
builders use a figure "at .050 lift" to measure
duration; which is what we are doing; and we have
used a cam profiler machine to show this on the
"stock" cams for comparison. Definitely not as flashy
a number bu t more accurate; since adding on the
clearance ramp on to duration is usually thought of as
a joke to engine builders anyway...
Same
with valve lift. Stated figures are THEORETICAL lift;
or GROSS lift; or WHITE CLOUDS on BLUE SKY lift. They
do not account for valve lash; they attempt to account
for a rocker arm ratio which may or not be in play
with any particular rocker arm at any given time in
the cycle or with any given
valve/lashpad/head.
Better
in comparing camshafts is using LOBE LIFT (CAM LIFT);
that is what the lobe rise is over the base circle
(what is there if all the lobes were
removed).
So
with the above discussion on bogus specs in place; we
have:
There
were two cams in the production cars the "SU" or "A"
cam (256 duration .44 lift); and the "Solex" or "B"
cam (280 duration .46 lift). The names indicate the
type of carburetor the two cams went with. You can use
the Solex cam on the SU cars; it moves the power band
a bit uphill and increases it a bit; with only a small
loss at the lower rpms. Using the SU cam with the
Solex carbs; you get the worst of both worlds. No
bottom end and no top end.
Datsun
Competition (Nissan Motorsports) also sold a third
flavor; the "Solex II" cam also called the "C" (296
duration .48 lift). The letter designations come from
the marking on the end of the camshaft. You have to
use a small mirror to see it with the cam mounted on
the cylinder head as it is right up against the
cowl/firewall of the car.
IDENTIFYING
CAMS:
Without
throwing the cam in a cam profiler you can't tell
exactly WHAT you have but there are some hints. The
above mentioned "A", "B","C" can help but only shows
what the cam STARTED OUT AS. If the base circle
(diameter of the cam 90 degrees from the lobe) is
still about normal (1.305 give or take a hair) you can
check the overhall height. Stock SU cam will read
1.620-1.625; stock "B" Solex will read 1.636-1.640 at
least that is what we are reading after checking a
large number of them; even new ones.
Printed
Nissan specs say the lobe lift is .315 SU and .327
SOLEX which are WRONG; checking numerous cams proves
this. A production change? No, because the equally old
drawing of the OEM camshaft shows .328" SU and .340"
SOLEX which would make the measurements 1.628 SU and
1.640 Solex for IDing unmarked cams; adding the
assumed base circle of 1.300; or 1.633 and 1.645 with
a 1.305 base circle. The lower figures may be an
attempt at figuring in the loss due to the lash
settings; but it still isn't correct; but the wide
range we have seen "stock" SU and SOLEX cams read
makes anything a guess. When we have these recut we
have the cam grinder follow the original pattern that
was cut into the cam. This reduces changes that could
occur to base circles or having to actually weld a
lobe to cut it as if the original specs were cut in
stone and followed accurately to begin with. Again;
these figures are just for comparing cam profiiles.
Seeing how these cams vary; you can have two
"identical" cams that have varying duration measured
at .050" and then at a higher or lower measuring spot
the cam that was "lower" shows higher; as if the
shapes of the lobes vary as well.
As
mentioned earlier even on new cams the base circle
varies; why I don't know; but a took a batch of new
Nissan cams for a date with a cam profiiling machine
and got some interesting results! The 1.305 figure
seems about the a third of the cams. I think it is all
production variances. And the lobe lift I think varies
as those figures .328/.340 may not include any
polishing necessary or maybe changes due to
hardening??? Or just machine tolerances. Nissan's pubs
show 33mm as the diameter (1.300). The 1.305 I think
is just how the machinery and cutting procedures
sometimes have worked out. I've also seen a USED cam
at 1.310! (Remember; lobe lift times rocker arm ratio;
typically about 1.4; gives the lift at the valve; well
the "gross" lift anyway; which is "supposed" to be
.44" on the SU and ".46" on the Solex cams.
And
keep in mind it is about impossible to accurately
measure cams with a micrometer; I think max lift isn't
at TDC on the lobe! A cam profiler is the best way or
setting up a dial indicator and an old school V-block
jib. Engine builders would most likely measure the
activity at the end of the rocker arm or at the valve
head. Those talented fellows make me wish I'd paid
more attention when I was gifted with being able to
work or learn under some of them. In My Next Life, FOR
SURE.
USED
AND REGROUND CAMS
We
have no idea what kind of stress a used or reground
cam has been under previously. Camshafts do not crack
from old age; they crack from being run in a head with
misaligned towers or a warped head where the top was
not restored for proper cam operation (i.e. being able
to spin the cam with two fingers when it is torqued
down, oiled, WITHOUT rockers.
For
this reason USED CAMS or REGROUND CAMS HAVE NO
WARRANTY AGAINST BREAKAGE.
The
only way around this is to buy a new cam; including
having a new SOLEX cam cut into a SU profile; or make
sure your head is completely correct and take the
gamble. It isn't a common thing; it isn't like people
are coming to us everyday for camshafts for this
reason.
USED
CAMS
These
are just used cams we have not taken to the cam
grinder. We do not though sell used cams that have
chips out of them or other lobe damage or bearing
journal damage visible to a non-cam machinist; other
than small scratches that many times can be polished
out. Technically speaking you should always use a used
cam with its previously run rockers; in the exact
positions they were in; but it is rarely possible
unless we have recently pulled the head apart
ourselves and saved it specifically for that purpose.
REGROUND
CAMS
Changing
the cam means changing rockers if you want it to live;
as does proper break in and lube during break-in.
There is little point to using a reground cam (or new
cam) with old rockers. They all "look smooth" but they
will imprint themselves on a new or reground cam
immediately.
If
you are looking for a Solex cam; reground Solex cams
where the original was also the Solex grind are best;
but more expensive as the Solex cam itself has always
been more expensive. The base circle is always less
disturbed the closer the regind profile is to the
original. This can of course be dealt with (read on)
and doesn't much matter if you're looking for the
Solex grind for less $$.
In
addition to our own contracted work; we have many cams
that came from all over the country. All we can do
with those is spec them out so everyone can see what's
what. Every cam grinder is different in how they go
about their business.
Changes
to the relationship between your cam and valves; known
as "CAM GEOMETRY" can occur when using a reground cam;
although with a careful cam grinder and staying close
to the original grind this isn't usually a problem.
(like these stock grinds) Many other problem areas
(your head may already have these) can cause far worse
changes. Link following for more info:
CAM
GEOMETRY LINK
MAKING
YOUR CAM LIVE
Having
a cam live also depends your rockers; if they have run
with another cam they can increase wear in certain
spots; if they are the old style 1-piece rockers those
can trash a cam as well. Look at them form the side;
does the area (wear pad) that contacts the cam look
like it has been welded on to the "arm" part of the
rocker arm. IT SHOULD. Nissan changed these in mid-69
at engine U20-11849.
Running
with improper strength springs will also trash a cam.
Unless you are absolutely sure your springs are Nissan
springs or built for this engine by intelligent
sources; ask your shop to check springs at full lift;
so you don't have a case of the springs "stacking"
i.e. the springs can't stand that much compression and
one coil is hitting the next. Instantaneous cam
failure is the result. At full lift there should still
be .060 or more clearance between the coils. And
although the rated pressure of a spring can be
correct; it is usually only correct for a stated
design; i.e. valve lift. When forced to go farther;
even though it may allow it and not "coil stack" the
pressure may increase dramatically. Fantastic valve
lifts sound impressive but stay away from this unless
you have a head shop in your back pocket that is on
top of all of this and has the knowledge and
availability to select alternate springs if necessary.
In combination with custom springs; the valve stem
locks (collets) can be altered as well to raise the
height up and to allow for higher lifts (somewhere
around .5". I think the Bob Sharp manual recommends
collets made by Allied #117.
I've
never been a fan of any "wild" grinds for these
engines as SO MANY of them are running around with the
heads milled (so the valves are closer to the piston)
but more importantly and more to the result of
valve-to-piston conflicts; the valve timing is off.
Shimming the upper tensioner may make you feel good
about chain rattle but it does nothing to correct
valve timing problems from a loose chain or milled
head. Most shops will say .100" clearance is necessary
between the piston top and valve. Some shops say .125"
on the exhaust valves. In some cases to make
everything live together the pistons will have to be
flycut for clearance if you can't/won't fix the
underlying problem. Again; a good head shop can be
your savior.
Before
starting an engine that has sat or is having a cam
change; remove the distributor and the oil
pump/distributor drive gear and spin the pump with a
long screwdriver between your palms or use a
reversible drill running counter clockwise until oil
is pumped through the system. Take note that the oil
is able to come out of ALL the cam lobes. When the
little oil pump driveshaft is removed take note (or a
picture!) of it before removal. The slot in it is not
in the center; so note how that looks and keep in mind
that to get it out you have to twist it and it will
spiral out. The picture in the factory shop book
wasn't taken if I remember right at top dead center of
#1 piston so it is useless. You have to kind of make
your own "repair file" as you go along with these
cars... And don't forget the break-in procedures your
cam provider has given you.
One
of the oil pressure loss factors we tripped over
decades ago was when we encountered a car with no
plugs in the end of the camshaft. After the oil
passage way is drilled in a cam, crankshaft, many
other items; they plug the end so the oil just doesn't
exit out; losing whatever precious pressure there was.
Nissan used to provide the plugs WITH the cam but not
IN the cam. Many of these did not get installed. So
always check yours. We of course check them here but
it is always a good thing to check. Using a tiny
screwdriver or long nail; you shouldn't be able to
push it in farther than the center of the end journal.
We have those listed on the 2000 CYLINDER HEAD "SMALL
PARTS" page in the NEW PARTS sections of the website;
as well as the plugs for the head if you are missing
one and a bunch of other tiny parts that can go
bouncing off your workbench...
FOLLOWING
INFO FROM OUR NEW SOLEX CAM PAGE; A LOT OF IT IS
APPLICABLE TO BOTH SU AND SOLEX CAMS...
