Usage:
3508 (1ZF),
3512 (3YF),
3516 (4XF) Engines
A new 3500 Family of Standby Generator Set Engines is available with higher kW ratings. These new configurations are significantly different from the lower rated 3500 Family of prime power generator set engines. Some new components are stronger to allow operation at higher cylinder pressures. This provides improved engine efficiency which results in lower Brake Specific Fuel Consumption. These new configurations have a different serial number prefix because of these differences.
This article describes the differences which have resulted in the higher ratings. It also addresses the adaptability of the new components to the lower rated engines.
Illustration 1. Typical standby generator set.
Pistons have been redesigned into a two-piece component. The crown is made of a cast steel alloy, while the skirt remains a forged aluminum alloy. See Illustration 2. The two pieces are held together with a new piston pin. Two bronze/steel overlay bearings are used in the steel piston crown pin bores. The piston rings are placed higher on the new piston and a rectangular intermediate ring is used. The higher ring position provides increased fuel consumption efficiency and cleaner combustion. The added strength of the steel piston crown will allow for increased loads.
Illustration 2. New two-piece piston.
New oil cooling jets are used with the new piston. The new jet sprays two streams of oil, just as before, but has been designed to deliver more even oil flow. The new jet will provide good cooling with either hot or cold oil.
Connecting rods have changed to work with the new piston design. The small end taper angle has increased to provide more bearing area.
Smaller air cleaners are used for this standby generator set application. These air cleaners are designed for 50 hour interval changes when operating in clean surroundings. They should be checked regularly and changed more often, in a dirtier environment.
Larger and more efficient turbochargers are used. A high mounted aftercooler provides a more direct path for intake air to flow into the cylinder heads. See Illustration 3. Streamlined air intake pipes and exhaust manifolds also reduce air flow losses. See Illustration 4. This changes help increase operating efficiency and reduce exhaust temperature when compared with lower rated engines.
Illustration 3. Comparison of air intake paths through standby generator set engines and other lower rated 3500 Family of Engines.
Illustration 4. Comparison of exhaust manifold sections from standby generator set engines and other lower rated 3500 Family of Engines.
The top deck of the cylinder heads has been shot peened to provide increased strength.
Fuel injectors with nine-hole tips are used. The lower rated 3500 Family of Engines use injectors with tenhole tips. At the higher ratings, the nine-hole tip injectors provide cleaner combustion.
A fabricated steel fuel manifold is used in place of the multi-piece aluminum fuel manifold. See Illustration 5. The steel manifold is stronger and has fewer joints to seal. This will provide improved reliability.
Illustration 5. New fabricated steel fuel manifold.
Spin-on oil and fuel filters are used for quick, easy serviceability. An attachment fuel priming pump is available.
Water temperature regulator housing bolts have been relocated to improve serviceability. The bolts are now installed from the top, reaching through the regulator housing into a tapped plate. Previously, the bolts were installed from the bottom through the plate into the tapped regulator housing.
This new higher rated 3500 Family of Engines has been designed for use in standby generator set applications only, and should not be used for prime power or peak shaving applications. The new high horsepower engines have new serial number prefixes as shown in Chart A.
Caterpillar does not recommend upgrading any earlier 3500 Family of engines to this new higher power configuration. The parts which differ include pistons, connecting rods, piston cooling jets, complete air intake, aftercoolers, exhaust manifolds, and turbocharger systems. Replacing all these components would not be cost effective. Also, many of these new components are only approved for standby generator set applications. Chart B lists the new components and their adaptability to earlier 3500 Family of engines.
