Some
Great TIPS For Rebuilding
a Two-Stroke Kart Engine Top End
Before
you disassemble your engine, power-wash the engine and the
rest of the vehicle. That will reduce the risk of dirt and
debris falling into the engine. Once you remove the cylinder,
stuff a clean rag down into the crankcases.
The cylinder
and head use alignment pins to hold them straight in position
from the crankcases on up. The pins make it difficult to remove
the cylinder from the cases and the head from the cylinder.
Sometimes the steel alignment pins corrode into the aluminum
engine components. Try spraying penetrating-oil down the mounting
studs before attempting to remove the cylinder and head. Never
use a flat-blade screwdriver, chisel, or metal hammer to remove
the cylinder. Instead use this technique; buy a lead-shot
plastic mallet, swing it at a 45-degree angle upwards against
the sides of the cylinder. Alternate from left to right, hitting
the sides of the cylinder to separate it from the cases evenly.
Clean the steel alignment pins with steel wool and penetrating-oil.
Examine the pins closely. If they are deformed in shape, they
won't allow the engine parts to bolt together tightly. This
can cause a dangerous air leak or a coolant leak. The pins
are cheap at about $2 each. Replace them if they're rusty
or deformed.
Never
re-use old gaskets. Remove them with a razor blade or gasket
scraper. Don't use a drill-driven steel wool type pad to remove
old gaskets because they can remove aluminum from the cylinder
and head. That will cause a gasket to leak.
Always
check the ring end gap on a new ring by placing it in the
cylinder between the head gasket surface and the exhaust port.
The gap should be between .012 to .024 inches.
Always
install the circlips with the opening facing straight up or
down, that way inertia will hold it tight into the clip groove.
Place one clip in the groove before installing the piston
on the connecting rod. Its easier to install a clip with the
piston in your hand rather than on the rod. There also less
chance that you'll drop the circlip in the crankcases.
Always
install the rings on the piston with the markings facing up.
Coat the rings with pre-mix oil so they can slide in the groove
when trying to install the piston in the cylinder.
Always
install the piston on the connecting rod with the arrow on
the piston crown facing towards the exhaust port.
The traditional
way to assemble the top end is to install the piston assembly
on the connecting rod, compress the rings, and slide the cylinder
over the piston. That can be difficult with larger bore cylinders,
or if you,re working by yourself. Try this method instead.
Install one circlip in the piston, install the piston into
the cylinder with the pin hole exposed, install the piston
pin through one side of the piston, position the cylinder
over the connecting rod and push the piston pin through until
it bottoms against the circlip, install the other circlip.
It only takes two hands to install the top end using this
manor and there is less chance that you,ll damage the rings
by twisting the cylinder upon installation.
On cylinders
with reed valves and large oval intake ports, take care when
installing the piston assembly in the cylinder because the
rings are likely to squeeze out of the ring grooves. Use a
flat-blade screwdriver to gently push the rings back in the
grooves so the piston assembly can pass by the intake port.
For steel
head gaskets, place the round side of the "bump"
facing up. Don't use liquid gasket sealer, use aerosol spray
adhesive types instead. For hybrid fiber/steel ring head gaskets,
place the wide side of the steel rings facing down.
When you
initially start the engine after a rebuild, manipulate the
choke to keep the engine rpm relatively low. Once the engine
is warm enough to take it off choke, drive the vehicle around
on flat hard ground. Keep it under 2/3 throttle for the first
30 minutes. Two common myths for proper engine break-in are:
* - Set
the engine at a fast idle, stationary on a stand.
* - Add
extra pre-mix oil to the fuel.
When the
engine is on a stand it doesn't have any air passing through
the radiator or cooling fins and it is in danger of running
too hot. When you add extra oil to the fuel you are effectively
leaning the carb jetting. This can make the engine run hotter
and seize
