Installation of an engine kit is well within the
capabilities of most do-it-yourselfers with
reasonable mechanical abilities and a few tools.
There are some important things to know, though, and
like anything else, there are little things here and
there that make the job easier. Recently I took a
few pictures as I put a top end on a motor and I
thought I'd share a few things about the job that
may be helpful to folks.
First, though, let me warn you that there are LOTS
of ways to do this, and reasonable people sometimes
differ on the best procedures and methods. I've
tried most everything and what I'm going to show you
here are the methods I've found easiest and that
I've had the most success with. I have no doubt that
you can find many people who disagree with some or
all of this. But this is the result of doing this
many times in many ways and it's been the most
successful for me.
First and foremost in assembling the top end is
CLEANLINESS. I can't emphasize this enough. The
pistons, cylinders, and rings, as they come out of
their boxes, are FILTHY, and you do NOT want to
assemble them that way.
I always start by cleaning the bore with a strong
solvent such as brake parts cleaner or lacquer
thinner. Then I take the cylinder to the sink and
using hot soapy water, I literally scrub the
cylinder wall, and then thoroughly rinse the soap
off. It's not unlike doing the dishes. You want it
clean enough to eat off of. Likewise I do the same
with the piston. I also put one wrist pin circlip
into the piston now, while the piston is easy to
Next I set them out on clean towels and proceed with
the ring gapping. Ideally you want the cylinders in
torque plates while gapping the rings, as a .001"
change in diameter of the bore is literally over
.003" of gap change. What happens when you stick a
ring into a distorted bore is that the tight spots
will touch the ring and the loose spots will not. So
if the bore is distorted, it generally makes the gap
measure smaller than it really is. So you may end up
with a gap that's ever so slightly larger than what
measured. But in reality, that's a good thing, I'd
rather see people err on the too-big side than on
the too-tight side when it comes to ring gaps..
Pay attention right here to piston orientation. With
most of the pistons we ship, the valve pockets are
the same size and the skirts are the same length, so
you can put the piston in either way. However, with
some custom pistons we offer, as well as some big
bore pistons, orientation does matter. If one valve
pocket is bigger than the other, make sure you put
that pocket on the intake side. Likewise if the
piston has a clearance cut on the skirt, or has one
skirt shorter than the other, that side goes toward
the intake (I'm assuming we're not talking about an
XR type setup here).
Big bore pistons will sometimes get a clearance
cut on the intake side skirt, be sure to orient this
type of piston correctly in the bore.
I always start with the oil rings and work my way
up. First I clean the expander with some brake
cleaner and compressed air, and then I put it on the
piston, taking care to put the expander gap over the
wrist pin on the pushrod side of the motor as
directed by the instructions.
The oil rails rarely need their gap adjusted as
anything from about .015 and up is acceptable. But
you should spot check it anyway. I just insert it in
the top of the bore and nine times out of ten I can
tell by looking that it's fine. If it looks close at
all, I'll push it an inch or so into the bore,
square it up carefully, and make the measurement.
Oil rails are a hard spring steel and difficult to
file, if I have to adjust an oil rail gap (rarely)
then I'll touch it on a grinder equipped with a fine
stone, and then deburr with a file.
Once you know the oil rail gap is okay, the next
step is to CLEAN it thoroughly. I know, I sound like
a broken record, but it's AMAZING how dirty rings
can be when you pull them from the package:
This is a second ring, not an oil rail, but you get
the idea. I put a little brake cleaner on it and
wiped it with a rag and you can see how dirty it
was. Oil rings come out of the package the same way.
Oil rails are normally put on by hand, not with a
ring expander. Simply feed one end into the ring
groove, just above or below the expander, and work
around, sliding it on. The main thing is to pull
outward as you do this enough to keep the ring from
scratching the piston on it's way. But an oil rail
is flexible and this is easy to do. Repeat for the
other oil rail, make sure you've got the rail gaps
and the expander ends in position per the
instructions, and the oil rings are ready. The ends
of the expander will often try to jump out and
overlap each other rather than butt up to each other
as you do this. Just be careful and keep an eye on
it, it needs to be butted.
Now set the gap on the top and second rings. The
basic idea is to place each ring in the bore,
measure the gap with a feeler gauge, pull it out and
file on it, and repeat until the desired gap (per
NRHS General Instruction Sheet) is achieved. But
of course there's a little more to it than that.
Squaring the rings properly in the bore is
absolutely essential to getting an accurate
measurement, I can't emphasize this enough. It take
very little error in the squaring to affect the ring
gap measurement drastically, you can EASILY get
fooled in your measurements if you don't square the
The temptation is to place the ring right at the
very top of the bore, because it's so easy to square
it when you have the cylinder deck as a reference.
BAD IDEA! The very top of a cylinder is notorious
for having distortion and/or being slightly
different in size. You MUST push the ring down the
bore, at least a half an inch, and then you have to
get it square.
I've seen people use various methods for doing this.
You can go out and buy a ring squaring tool, but
unless you do a lot of these, it's probably not a
good investment. Some people use a bolt as a
depth gauge, pushing the ring down at various points
around the bore and using the head of the bolt as a
stop against the cylinder deck. Not a bad method,
but a little tedious. Here's what I recommend for a
simple, no cost, easy and accurate method:
A piston with only it's oil rings installed and
inverted in the bore makes an excellent ring
squaring tool. Note the clearance cut on the skirt
on the left; at final assembly, this side of the
piston needs to be oriented toward the middle of the
Now you know why I recommended installing the oil
rings on the piston first ;) This is a simple and
effective method for pushing the ring down the bore
and squaring it up for a measurement.
Never, ever, ever, use the bottom side of the
cylinder for your ring gap measurements. The spigot
of a Harley cylinder is unsupported by aluminum and
is almost always distorted and/or not the correct
size. Remember, it takes very little error in bore
diameter or roundness to have a BIG effect on that
gap measurement. You want to do it a half inch to an
inch down from the top of the cylinder, that's a
Adjusting the ring gap is best done with a gapping
There are a couple different styles of gapping
tools. The above is an inexpensive hand crank type
tool that does a good job. Electric units are also
available, although it's hard for most
do-it-yourselfers to justify the expense.
Truth be told, a number of people have been very
successful doing this job with a fine tooth file as
well. Simply clamp the file in the vise, and then
carefully work the rings back and forth squeezing
the gap around the file.
Regardless of which tool you choose, there are two
things to be careful of. First, KEEP THE GAP
PARALLEL. Many many times filing on a ring will tend
to make a "V" shape out of the gap. Keep an eye on
it and work to keep the two sides of the gap
parallel to each other.
Second, DON'T OVERSHOOT THE GAP. I know it sounds
basic but this is a very common mistake. Go slowly
as you approach the proper gap and check yourself
often. It takes a little patience but it's worth it.
Also be aware that second rings often file MUCH
faster than top rings. If you gap your top ring and
get a feel for how much filing it took to move the
gap a certain amount, and then try to apply that
information to the second ring filing, you're
guaranteed to overshoot the gap. Patience is a
virtue (and virtue won't hurt you).
Okay, once you've got the ring gap correct, next you
need to deburr it carefully:
Anytime you file on metal, you create burrs. These
burrs will hang up on, and even damage the ring
lands, which hurts ring sealing. It's critical that
you remove these burrs, on all four sides of each
end of the ring. A small fine tooth file used
lightly works well for this. You don't want to
chamfer the end of the ring, but you need to get rid
of that burr!
One last step before you put the rings on the
piston: CLEAN THE RINGS! Did I say that already?
They're filthy. They're even more filthy now that
you've been handling and filing on them.
One area where I most certainly do not recommend
cutting corners on the tools you use is the use of a
Installing a ring with a ring expander. Note how
this piston has one valve pocket larger than
the other. The larger pocket always goes toward the
A ring expander is not expensive at all, I paid less
than $10 for this one at my local Sears store. Just
do it, don't try to do this without it, as it's
almost impossible to do without damaging the piston
and/or the ring. Oh, and always CLEAN the tips of
the ring expander before using it. If it's been
sitting in your toolbox, chances are it's dirty, and
it'll get the rings dirty.
Another EXTREMELY important point about ring
installation: put the ring on right side up! Most
rings have a dot imprinted onto one side; this dot
always goes UP. Even if there's no dot, rings
usually need to be installed a certain way. The
instructions with the rings will show this. Double
check this. Triple check this. Put a ring on upside
down and the motor will burn oil like you can't
So now you've got the rings all gapped (and
cleaned), and installed on the piston. Your ring
gaps are in the right place per the instructions.
You're ready to put the piston into the cylinder.
This is where things are going to get a little more
controversial. Again, this is how I recommend doing
it, but you'll have no trouble finding others who
have different methods.
The service manual will talk about putting the
piston onto the connecting rod, putting some support
plates underneath it to stabilize it against the
case deck, putting a ring compressor around it, and
then putting the cylinder over the piston. And this
method certainly works and I know many techs who
prefer to do it this way. However, the method I'm
about to describe is what I've found to be easier,
and it also needs less special tools, which makes it
especially easier for the do-it-yourselfer.
First and foremost, I want you to liberally lube the
piston and rings, preferably with a high quality
engine assembly lube. Now you will have no trouble
finding all kinds of dissenting opinions on initial
lubrication of pistons & rings. Many people will
tell you that assembling it dry promotes better ring
seating. Others will say minimal lube should be
used. Total Seal sells a product called "Quick Seat"
that you put on the cylinder walls to help the rings
with the seating process.
I've done all those things multiple times and the
conclusion I've reached is that you need lube. A
new, fresh motor is at MUCH greater risk of ring
microwelding than it is of failure to seat rings. If
the bores are round and the rings are good and the
cylinder wall finish is right, the rings are going
to seat just fine. What you need to do is keep it
from damaging the pistons during break-in due to
ring microwelding. It's a whole 'nother subject, but
the short story is that rings have very little
surface area of contact with the cylinder wall
during break-in, and as a result, those spots get
very hot, and if they get too hot, they damage the
piston's ring land, which is a sealing surface. When
you do that, you've forever condemned your motor to
be a mediocre performer. Proper lubrication and
gentle break-in are absolutely critical to getting
maximum performance from a motor.
A piston and ring assembly lubed generously with
Red Line synthetic engine assembly lube (available
from NRHS) and positioned to be inserted into the
Once the piston & ring assembly are thoroughly
lubed, position them as shown above, taking note of
the piston orientation. It might be a good time to
triple-check yourself on the ring orientation first,
by the way, both that they're right side up and that the
gaps are where they should be, since here in a
second you won't be able to see them anymore. Now
gently work the top ring into the spigot, rocking
the piston slightly as needed. If you got your
cylinders from us, or if we bored them for you,
there's a chamfer right there at the entrance to the
spigot that makes this job easier. It's really not
hard at all. Now do the same for the second ring and
oil rings. If you need to push on the ring, avoid
the temptation to push with a screwdriver or
anything made of metal for that matter, the risk of
damaging the ring is just too high. Use a hard piece
of plastic, for example the cap of a Bic pen works
well. Don't get crazy doing this, be careful and
it'll go in and there will be no damage.
Once you've got the rings into the bore, push the
piston all the way down the bore and lube the
cylinder wall under the piston liberally as shown.
If it's hard to push down, you may have a ring
cocked, and that's not good of course! But there's
something else that can make it hard to push down:
air. If you have the cylinder positioned like this
and there are no dowels in the top side of it
(bottom side as shown), air will be trapped above
the piston and make it difficult to push down. Cover
that possibility before you go pulling the piston
out to see if you damaged a ring. If you were
careful putting the rings in, the possibility you
got it cocked in there is unlikely, though.
One more note before I go on. All of the prep shown
so far can be done by NRHS if you desire, for a
nominal charge. We do it to this point for people
all the time and we charge an hour's labor. We then
seal the assembly into a clean plastic bag for
shipment, so it arrives ready to go on as follows.
What I'm doing here is using Three-Bond 1104 instead
of a base gasket. Why? Well, it has to do with
getting the squish right. This motor would've had
too much squish clearance had I used a gasket. Read
my piece on setting your squish.
Now that you've got the cylinder wall thoroughly
lubed below the piston, push the piston back out the
spigot, enough to allow the wrist pin to slide in or
out, but not allow the rings to escape. Note that it
is not necessary or even desirable to lube above the
piston. In fact, after you push the piston back to
this position, wipe the excess lube from the
cylinder wall above the piston. Slide the wrist pin
part way out as shown. Now take the assembly over to
the waiting motor, which has already had it's gasket
surface cleaned up and is positioned with the
connecting rod halfway up ...
Place the assembly over the connecting rod like
this, sliding the cylinder down over the studs. It
helps to have three hands. Shown is my shop foreman
Wiggle, raise, lower, and twist the cylinder GENTLY
while pushing in the wrist pin. When it's positioned
just right it'll slide right through. Once it's in,
place a rag under the piston and carefully insert
the circlip, and double triple check that you've got
it all the way seated in it's groove. Not a mistake
you want to make! Through this whole process, do
things gently enough that you don't accidentally
pull the piston down and let the rings pop out of
Next gently squeeze the piston up into the cylinder
as shown. Doing it this way keeps you from banging
it around and possibly letting the rings pop out.
Push the cylinder down and carefully guide the
spigot into the case. Don't slam it onto the case
and don't force it or wedge it, spigots are thin and
And finally push the cylinder all the way down.
Piece of cake.
If you turn the motor over, it'll likely push the
cylinder back up off the case deck. Here's an easy
and effective way to keep the cylinder in place
while you work on the other one. Use your shorter
(spark plug side) head bolts with some cheap 1/2"
PVC unions as spacers to hold the cylinder down. The
PVC will not damage the cylinder deck.
Like I said at the beginning, this whole process is
well within the capabilities of the average
do-it-yourselfer with reasonable mechanical
aptitude. Hopefully this article clarifies some of
the finer points and gives some handy tips for doing
it well. Be sure to read the
NRHS General Instruction Sheet as well, and
don't hesitate to call us if you have any questions.
It's in our interest to make sure you're successful
and we're happy to answer questions or give advice.
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