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Introduction:
Steps
one through five must be done prior to proceeding. Note,
it does not matter if the gearbox oil is drained oil filled. Begin
by laying out all the parts on a clean dry surface (see
picture 1). You should have at the very least a big-bore
piston, piston ring(s), a wristpin, two new piston circlips,
a new base gasket, and a new head gasket.
Preparing
the cylinder head:
Start by preparing the
new cylinder head. First, put a very light coating of
gasket sealer on the temperature probe and thread into the new
head. Snug tightly. If you are using a Top Performance
big-bore kit, you need to also install the small water spigot
that you removed from the stock cylinder head (circled blue
in picture 2). The next
step is installing the original stock thermostat on the new
cylinder head. Simply unscrew the two Phillips screws
and reinstall on the new head.
VERY IMPORTANT....Notice
the bleed hole in the flange (see
picture 3), locate the thermostat in a position that allows
fluid passage. It will appear like it is only 50% open,
and this is perfectly normal.
Preparing
the piston and cylinder:
Start by determining
which way the ring goes. Every piston ring will have a
stamp mark near the ring gap. It is usually a stamped "N" or "T". This MUST be
installed facing upwards (see detailed
picture 4). Also, locate the "locating pin" in
the piston groove. The ring gap will go here.
To
install the piston ring, slip one end of the ring into the
piston groove,
and work towards the other end. The ring gap will be
centered over a locating pin in the piston groove. Try
to open the ring as little as possible. Be very careful
during this step. The ring and piston will eventually
be going up and down over 11,000 times per minute.
Now
would also be a good time to learn about the arrow mark
on the top of
the piston. This always points towards the exhaust port. Since
the exhaust exits out the front on the RS50, the arrow will
be facing forward in the bike.
Next,
install one circlip into the piston. It does not really
matter which one.
The cylinder
preparation consists of installing the exhaust o-ring into
the exhaust port (see picture
5). It rests in a small groove in the exhaust port. Applying
two-stroke oil to the o-ring will aid exhaust installation
later. Lubricate it well.
We
also like to coat the cylinder walls with two-stroke oil
as well. Rub
some oil all around the walls with your finger. You
can not really over-oil it.
Installing
the piston:
Start by thoroughly and
heavily oiling the small-end bearing. Also, thoroughly oil the
wristpin. With the piston facing the correct direction
(see above), slide the piston over the connecting rod. Insert
the well-lubed wristpin through the piston with your fingers. Finally,
install the second circlip.
Now
is a good time to double check that both circlips are fully
seated in
their respective grooves in the piston. You do not want
them coming out!!!
Installing
the cylinder:
Start by installing the
new base gasket. Note, it can only be installed one way.
The
next few steps are probably the hardest of all. It
is VERY important that they are done correctly. The
job is easiest, if you place the crank and piston at top dead
center (TDC). In other words, pull the piston up as high as
it will go out of the crankcase. The bike must be in
neutral.
To
start, you are going to have to fully compress the piston
ring in order
to install the cylinder over it. You are also going
to have to make sure the ring gap is located on the "locating
pin" in the piston groove (see
close-up picture 6). Squeeze the piston ring between
your thumb and first finger. With the other hand lower
the cylinder over the piston. Once the piston is inside
the cylinder a little way, it should lower with VERY LITTLE
effort. DO NOT force it down!!! Try to lower the
cylinder down evenly and squarely. If it does not go
on easily, one of two things is happening. Either the
ring gap is not centered on the "locating pin",
or you are not fully compressing the ring during the cylinder
installation process. This job maybe the easiest with
two people. One person is in charge of compressing the
ring and locating the ring gap, while the other person slowly
lowers the cylinder onto the studs (see
picture 7).
Push the cylinder
down fully onto the base gasket.
Installing
the cylinder head:
Start by installing all
of the head gaskets. On the Top Performance kit, one small
o-ring is installed over each cylinder stud. The Malossi
kit has these small o-rings integrated into the inner head gasket. It
should be obvious how the inner and outer head gaskets are arranged. Do
not forget the outer head o-ring, which seals the coolant inside
the cylinder cooling jacket. Lower the new cylinder head
onto the cylinder studs and ensure that all o-rings are seated
properly. Install the washers and the cylinder head nuts
(see picture 8). Initially
torque all four nuts to 10Nm in a criss-cross pattern. Finally,
torque them to 14-16Nm. It is important to torque them
in stages like this to insure flat and even pressure. Install
the spark plug and torque to 20-25Nm. Reinstall the big
coolant hose on the top of the head. Use a new hose clamp. The
small hose comes from the T-fitting on the right side coolant
hose. On Malossi and other kits with no small hose connection
on the cylinder head, special steps must be taken. A straight
hose-to-hose connector will have to be obtained from an auto
parts in order to remove the T-fitting from that radiator hose. We
do not re-install the hoses for the carburetor manifold plumbing.
Note:
If you do not feel
comfortable with these steps, please seek the advise of a professional. Anyone
with 2-stroke dirt bike experience would be more than qualified
to help.
Proceed to Step
8: Installing the Carburetor
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