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ABC,
RINGED, and LAPPED refer to piston/cylinder assemblies.
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ABC has become
the most common type of piston/cylinder arrangement for smaller
engines in recent years. Some ABC type engines actually use
nickel plating instead of chrome for the wear surface. Nickel
is less expensive because it is more environmentally friendly,
however chrome has a much slicker surface for less friction.
The ABC type
piston and cylinder are manufactured as a matched set, you
can not purchased a piston or cylinder separately.
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ABC,
ABN and AAC engines all fall under the same design category
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ABC
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ABN
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AAC
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A -- refers to Aluminum Piston
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A
-- refers to Aluminum Piston
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A
-- refers to Aluminum Piston
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B
-- refers to Brass Cylinder
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B
-- refers to Brass Cylinder
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A
-- refers to Aluminum Cylinder
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C
-- refers to Hard Chrome plating
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N
-- refers to Electroless Nickel plating
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C
-- refers to Hard Chrome plating
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You
can tell an ABC engine by looking in the exhaust port.
The cylinder will be brass and the inner wall of the cylinder
will have chrome plating. The piston will be aluminum
color and usually has oil retention grooves cut into it. |
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An
ABN engine is a little more difficult to distinguish.
The cylinder is completely plated inside and out with
Nickel so it may appear to be Steel. No brass is showing.
The piston will be aluminum color and usually has oil
retention grooves cut into it. On this example the top
flange has been machined exposing the brass.
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You
can tell an AAC engine by looking in the exhaust port.
The cylinder will be light aluminum color and the inner
wall of the cylinder will have chrome plating. The piston
will be aluminum color and usually has oil retention grooves
cut into it. |
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The
other AAC type is like in the K&B Sportster. The cylinder
and fins is all one piece and the piston is hard chrome
plated. This type of piston does not have oil retention
grooves buy has a hard chrome appearance. |
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ABC type engines
are intentionally manufactured with a “taper” in
the cylinder so you will feel a "binding” when the
piston is moving through the top of its stroke. You may also
detect what seems like a dead spot or disconnected feeling
of the crankshaft and you may even hear a clicking sound when
the piston is at this point.
These feelings
and sounds are the result of the taper (binding) in the cylinder
affecting the required clearances in the connecting rod ends.
All of these conditions are normal.
As the ABC type
engine obtains operating temperature the cylinder becomes
straight and the clearances between the piston and cylinder
become correct. The straightening is due to the top of the
cylinder running at a higher temperature than the bottom,
thus the top expands more.
It is also normal
for compression to sometimes feel poor when the engine is
stopped and turned over while still hot. This is due to the
piston cooling faster than the cylinder. If the engine temperature
is allowed to stabilize the compression will return to normal.
ABC type engines
must be broken in properly. Click
here to learn how.
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There
are two basic ring types, DYKE'S and CONVENTIONAL
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A
DYKE'S type ring is a "L" shaped ring that fits
at the very top edge of the piston. Many people can not even
see it as there is no piston material above it. Dyke's rings
do not feel like they are working (no compression) when the
engine is turned over by hand. A dyke's type ring is pressure
activated, (it is like a dyke) when pressure pushes against
the inner side of the ring it is pushed out tightly to the
cylinder wall. When it is running past the ports no pressure
is pushing it so there is less friction. This is why dyke's
rings produce more power than conventional type rings.
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A
conventional ring is just that. It has a rectangular profile
and fits into a groove usually about a 1/16" down from
the top of the piston. Conventional rings, when broken in
properly, provide a good seal at any speed. Conventional rings
have constant tension that force them against the cylinder.
When you flip a good conventional ringed engine over it feels
great with snappy compression.
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| A lapped engine
has a steel liner and an iron piston that are lapped together
to a perfect fit. When you flip a lapped engine over you will
feel a perfect seal and good snap of compression. |
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| These type of piston/cylinder
sets are matched and can not be purchased separately. |
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| Lapped engines must
be broken in properly. Click
here to learn how. |
