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.
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.
General
Info on U20 Heads can be found on the Partial Rebuilt
Heads
Info
page.
