When the Series 53 engine was first put into production it had 2 valve cylinder heads, 17:1 compression pistons and “S” style injectors.
To achieve more horsepower and a cleaner burning engine the 4 valve cylinder head was developed along with an improved designed “N” and “C” style injector and the compression ratio was changed to 21:1. This proved to be an effective combination for this high RPM engine.
Because of this, most think or reason that all 2 valve 53NA engines use the 17:1 compression ratio piston and all 4 valve 53NA engines use the 21:1 compression ratio piston. While this is true in a sense, what you need to do is to match the injector to the piston to achieve optimum performance.
If you use the “S” style injectors (S35, S40, S45, S50) in your engine, you need to use the 17:1 compression piston/cylinder kit (5198903), regardless of which cylinder head (2 valve or 4 valve) you use.
If you use the “N” or “C” style injectors (N/C40,N/C45 or N/C50) in your engine, you need to use the 21:1 compression piston/cylinder kit (5198899), regardless of which cylinder head (2 valve or 4 valve) you use.
In applications that idle for long periods of time (such as forklifts and log skidders), 3-53 and 4-53 engines can begin to *wet stack. To help prevent this from happening cast iron compression rings were installed on the 3rd and 4th groove of the piston along with installing valve guide seals on the cylinder head. This will help reduce wet stacking.
If your engine has a problem of wet stacking and you have the “N” or “C” style injectors in it, we recommend you use the 21:1 compression piston/cylinder kit (5198904) with the cast iron compression rings, regardless of which cylinder head (2 valve or 4 valve) you use. Also make sure to install valve guide seals in the cylinder head.
*Wet Stacking is unburnt diesel fuel mixed with carbon that will slobber or leak out out the exhaust (and air box drain tubes in 2 cycle Detroit Diesel engines). This is caused from an improper load on the engine.