CYLINDER
HEADS unless specified otherwise are "just off the
engine" and have had nothing done to them. They haven't
been cleaned or anything else except for those
measurements and comments we have provided on the
individual pages.Click on the info link or part number
for each head to see the head and information for that
particular unit.
Any
parts listed are only in whatever condition they are in.
Heads may be offered at different prices depending on
what parts are included. Used heads would need to be
ordered by a mailed in order accompanied by a money
order. Please inquire for delivery costs. A US Postal
Money order is by far the quickest if you have any kind
of time constraint.
We
check for current thickness on all four corners as some
heads were not leveled properly either before milling
took place or releveled during the process if necessary.
Critical spot is of course on both sides of the forward
(#1) cam tower. We also check if there is a top "crown"
that needs to be knocked off; and existing bottom
warpage. Sometimes the top "crown" measurement if slight
can be ignored as some are measured end to end. Strictly
speaking; for cam related problems; you only need to put
a straightedge across the five cam tower spots; not the
entire gasket surface. Typically the "crown" figure is
derived from taking one-half the gap noted on the
opposite end of a straightedge that is held down on the
other end of the head. This is assuming the head is
warped evenly upward along its length but this is not
always the case. The measurement is a good indicator
though. Minor crowns may not cause cam to bind. It is not
a good idea to remove towers unless you absolutely have
to.
We
look for anything obvious; broken studs etc. I can't say
though that some thread problem somewhere won't get by us
as we don't run every open hole for problems. There may
be missing nuts, bolts, studs, washers etc. Suspect any
stud at least on the manifold to need replacing. Much
easier to do before you install the head than with head
on car! Many of these heads have sat in our storage for
10 20 30 years and they may have sat somewhere else
before that. Some were just pulled from cars or engines
and bugs, dirt, rust all have found a pleasant home on
some of them.
Always
assume cam towers have been off and reinstalled
improperly or out of order. Never assume a cam turns
freely (assuming top of head is not warped). Always check
and take necessary measures to correct the situation.
Always have heads cleaned out and passageways checked.
The first thing you do with a head to be worked on is to
mark all towers and caps. Sadly many roadsters get worked
on people who may have good intentions but poor
technique.
Unfortunately;
when a head is warped .020 or whatever; many machine
shops would just set their cutter to some arbitrary
figure and go to lunch. I've seen lots of heads that were
cut .060 to clear a .020 warp. And I have seen a shop
take a head and say "Oh it only needs to be cut .15; it
will be great...and NEVER measure the head to see what
was taken off PREVIOUSLY. The shops that wouldcheck the
top warp were few as well. I guess they figure since they
weren't putting the cam in it wasn't their
responsibility.
Some
of these we've taken off engines ourselves; or have been
from cancelled projects we've purchased or have fallen
out of the sky and landed here. They range from near
pristine to "Why are they listing that?" Truly the good,
bad and the ugly. Some of these would have been scrapped
20 years ago; lately quite a few people are putting
together roadsters out of junkyard cars and piles of
parts and are looking for any way to lessen their cost.
At least this way I won't be burdened by second thoughts
when I do toss a part out later!
In
the 70s and early 80s there was a big demand for cylinder
heads; mainly due to problems with the cars that could
have been corrected very easily. No easy way of
communication back then; but service update signs and
info in the dealerships WOULD have been possible. Similar
information could have been provided by ALL vehicle
manufacturers in car mags; or their own publications. The
only owners that learned of the simple ways to keep their
cars running were those mechanically inclined enough to
figure it out themselves; or had their car worked on by
someone like myself; who would sit them down on an apple
crate and bore them to death over the details. (Or who
would coerce, entice, beg them to sign up for our next
catalog/owners guide if I ever could actually stop
working on someone's car to finish the
thing...)
By
this time Nissan had lost or threw out/converted the
tooling for the heads. A complete new tool was created at
a cost that must have been unbelievable.
They
don't like being run low on coolant or anything else that
allows them to overheat; faulty distributor, improper
removal of "smog devices" some of which protect the
engine...; lean mixtures, plugged radiator, bad pressure
cap, plugged exhaust; the normal things that engines
don't like.
When
they overheat and warp; both top and bottom warp; putting
a cam back in a warped head usually results in it either
binding and "blueing" the towers; or breaking if the
stress is severe enough.
We
did some of the earliest "engineering" adventures with
oven straightening heads in the 70s; when most machine
shops had not seen many; if any; aluminum heads. Our
methods were crude and done out of desperation. We
learned in addition to warping the heads can sink, twist
and "shift" themselves. Cool.
When
a head is cut it is important that only the slightest
amount be removed; you don't even need to run the cutter
to the ends of the head to make the top suitably flat.
Removing material top or bottom puts the cam closer to
the jackshaft which creates chain slop and alters the cam
timing. It is uncommon to have a problem with valve to
piston contact because the valves have been moved too
close to the pistons; it is usually due to the valve
timing being altered. (When they open and close in
relation to the piston position) Various methods have
been used to counter this situation. We typically used
cam tower shims. Lowering the cam; or raising it more on
the top than it was originally to make up for bottom
cutting alters the valve train geometry...basically this
means the cam lobes will not be running in the center of
the cam follower (rocker arm) lobes. You can "cheat" and
let them go to the edge; but if they go over that the cam
says bye-bye in short order.
Altering
the placement of the wear pattern on a cut head typically
involves changing the rocker buttons' thicknesses.
(sometimes not all of them). If the valve is sunk more in
the head due to multiple valve jobs; it can help or add
to the problem.
Nissan's
service instructions were to never remove cam towers from
a head. This is due to the fact that you can take a new
head; remove the towers; reinstall them; and find the
camshaft bound up. It can be a rather tedious process to
reinstall cam towers and have the cam turn freely. Your
goal is to get it so the cam will turn with two fingers
with the journals oiled (and of course the rockers out!).
Getting it to turn as easily as possible involves
tightening the towers evenly, unevenly, and/or banging on
some offenders with a plastic mallet. Even with the
extensive use of locating dowels that Nissan provided it
can be work. Using "plastigauge" we were usually able to
locate the problem tower or cap. Normally if you get it
correct on the workbench; it will stay correct when the
head is torqued to the block; but not always. There are
all kinds of tricks like clamping them into the towers
and then bolting the towers on; but this can drive one to
temporary insanity as any other method...
In
a perfect world; the car would not overheat and the head
not need to be milled. In a perfect world you would just
as Nissan suggests get rid of the head when it is cut the
slightest amount. In a perfect world the new castings
would cost $80.00. They were $440 as far back as 1980 so
ways had to be found to make it all work. If everyone
that "needed a new head" in 1980 had only that choice;
there would be a lot less roadsters out there
today.
Once
a head has had it's top milled to true the surface; it
does not matter which towers go back on it. You will
usually have an easier time if you keep them in order;
but they were originally bolted to a flat surface; so
this sometimes doesn't matter except #1 and #5 of course.
You want to get the cam as relaxed as possible in it's
"bed" and if need be you can always have the cam journals
"align-bored". Some shops call this "line boring" but
it's purpose is to ALIGN the towers not to bore a hole.
If it is done properly the tiniest amount of material
will be removed. And again; this must only be done if all
attempts by a proficient individual have been undertaken
beforehand and almost always when towers and/or caps are
swapped.
The
original thickness of the U20 head is 4.528" (115mm).
They can typically do fine up to about .020" off without
a cam chain problem; assuming the chain and gears are in
good shape. After that point you want to think about
dealing with the situation.
If
need be we have used towers, studs etc.