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A white cloth passed down the bore should show
no marks! Do not bother to polish the piston dome, as
it will have no effect. For best results, put 1000 miles
on the motor before using full throttle.
The best pistons are (in this order):
1. KJKH replacements, which are slightly too tall for your cylinders, but will work fine with a thin (1/ 16" or so) shim of aluminum stock under the cylinders as a spacer. Be sure that the pistons are at least .020" down from the top of the cylinder at their highest travel! 2. Stock late (1955-73) pistons, or repro using late, thin (1/ 16") compression rings. 3. Stock early & military pistons using thick e/32") compression rings. Rings For best results your ring end gaps should come as
close as possible to the minimum specs listed in our
data table. Most ring sets will fall on the loose end of
factory specs (.020" or so). If you have a loose set (all
.015" or more), try to average them out - don't put
both the tight compression rings in one cylinder. You
may wish to use the next oversize ring set (that is, use
a set of .020" oversize rings with your .010" oversize
pistons, etc.). This will tighten up the end gap - more
than you think! Adding .010" to the ring size will
close up the gap by .031" (formula for circumference
of a circle: C = I1 * D). In all cases this will require you
to carefully file or grind material from the end of each
ring in order to obtain the proper minimum end gap.
If you don't have a ring compressor use popsicle
sticks or something soft to get the rings in - not a
screw-driver! Even small marks on the rings perma­
nently damage them.
Compression
All side-valve designs are limited to fairly low
compression by the chamber shape. More compres­
sion will help, up to about 6.5-1 (if it can be done
without hurting breathing). Besides high-compression
heads, another way this can be done is by milling
some material right off the top of the cylinders. For
some very complicated reasons, this works better than
you think.
The amount to remove is just enough to leave .021"
between the top of the cylinder and the top of the piston
at TDC. This will bring the piston to .040" of the un­
derside of the head when at TDC (assuming a head
gasket thickness of .019"; use you own gasket thick­
ness to do the math). If you're going to put in fresh
pistons, bore the cylinders now, put in the new pistons,
then measure the distance between the piston and the
cylinder's top surface at TDC. Subtract .021", and mill
off the figure you have left.
For example:
May 15, 2005
Distance from piston to cylinder top (@ TDC): .075"
Subtract clearance:
.021"
.054"
Remainder to mill off top surface:
If you prefer not to go through the measurements,
I'll cut out the math, and say that in almost all cases it
is safe & advisable to cut .030" off the top gasket
surface (any big automotive machine shop can do
this). This must be done before any valve seat work or
relieving!
Big Valves
A larger intake valve is very useful. A WR or K
valve is easy to install by cutting the existing seat to
about the same size as the valve head (be sure the seat
angle is cut correctly - the WR is 30°, the K is 45°,
like you have now). You can make a good valve from
auto parts (see Page 16). 18071-41V valves (available
from KNS Cycle) are lighter than stock, and come
with complete instructions and all necessary parts. In
some cases, one edge of the new valve will just touch
the pocket in the head (directly above it) when the
valve is fully open. A little metal can be easily re­
moved from the pocket with a Dremel tool to cure
this. Cut your existing seats to the same size as the
OD of the new valve head, at the same angle (300is
best for air-flow; if possible, re-cut the valve to 30° 1st).
Narrow the seat from the inside @ 70° to .080" width.
If they're in good condition, your old exhaust
valves can be improved by narrowing the seat area to
about .100" wide (from the inside). Use a shallow
angle to remove as much metal as possible without
cutting into the radius where the stem joins the head.
Use a 200stone (or the factory relief cutter) to narrow
the seats in the cylinders from the outside to 1.58" OD
(smaller than the valve OD), and then from the inside
with a 700stone to .080" wide.
Oil
H-D's new bikes all come with 20W50 oil - I like
it for all-round use. It makes the motor easier to kick
over in cold weather. For hot weather, (over 80°), use
H-D 105. If not available, use a good Pennsylvania­
type 60 wt. Such as Kendall, Quaker State, Wolfs
Head, Valvoline, etc. The best oil is marked "For
Service SG" on the can (this is the highest current test
standard). For low temperatures, use 40 wt. Change
the oil at least every 2000 miles, more often if you
have no air cleaner; change the filter (if you have one)
every other oil change.
If you want to know what's going on in your
pump, don't bother with a 100 lb. gauge screwed
directly to the motor - your normal reading will not
exceed 113 of the scale, the vibration will shorten the
life of the gauge, and you won't be able to read it
unless you hang half-way off the bike.
"45 Perfonnance", by VICTORY LIBRARY
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