Model Engine Company of America
ABC, RINGED,  and LAPPED refer to piston/cylinder assemblies.

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.


ABC, ABN and AAC engines all fall under the same design category
ABC
ABN
AAC

A -- refers to Aluminum Piston

A -- refers to Aluminum Piston
A -- refers to Aluminum Piston
B -- refers to Brass Cylinder
B -- refers to Brass Cylinder
A -- refers to Aluminum Cylinder
C -- refers to Hard Chrome plating
N -- refers to Electroless Nickel plating
C -- refers to Hard Chrome plating
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.

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.

 

  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.
  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.

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.


Ringed Engines
There are two basic ring types, DYKE'S and CONVENTIONAL
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.
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.
Ringed engines must be broken in properly. Click here to learn how.
Lapped Engines
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.
These type of piston/cylinder sets are matched and can not be purchased separately.
Lapped engines must be broken in properly. Click here to learn how.

The above information is provided as a guide. Since MECOA/K&B has no way of determining the ability of the individual using and understanding this information, we assume absolutely NO RESPONSIBILITY for any damage to person or property from the use of this information.
 

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