A generator head is the part of a generator that produces electricity. It contains the rotor and stator, which create a magnetic field that makes electrical energy. So, while a generator and an alternator are both types of electrical generators, a generator head is a specific component of a generator that is responsible for producing electricity.
Regarding generator heads, there are two main types: two-bearing and single-bearing. The main difference between the two is the number of bearings that support the rotor shaft. A single-bearing generator head has a bearing supporting one end of the rotor shaft. The engine supports the other end of the shaft when it is directly connected to the flywheel. There is an industry-standard to identify the different sizes of flywheels and mounting (bell) housings. They are referred to as SAE sizes.
Two-bearing generator heads are supported on both ends by two bearings with a rotor shaft sticking out of them. These two-bearing generator heads use belts and pullies instead of directly mounted to the engine flywheel.
When ordering a generator head, you must specify whether you want a single-bearing or double-bearing version.
For the single bearing, you must match the dimensions shown below and find what your SAE bell housing and SAE flywheel size are. Unlike the double bearing, where you can change a pully or belt, there is no room for error on the single bearing version.
Please use the information below to determine what you need before buying one. The same engines used by the two companies have different housings and flywheels, so you must double-check yours to be sure it is correct.
Mounting Configurations.
(Finding SAE Dimensions)
Engines and alternators use SAE standard sizes for the flywheel, flywheel housings and hole dimensions. You will need to determine what SAE Housing and SAE flywheel adapter you have. Use the guide below to find out what you need. Engines can be purchased with different size flywheels and housings so your engine is maybe totally different from the same engine model used by someone else.
SAE Flywheel Housing Dimensions
| S.A.E. NO. | A | B | C | Holes | Sizes |
|---|---|---|---|---|---|
| 00 | 31" | 34.75" | 33.5" | 16 | 1/2 - 13 |
| 0 | 25.5" | 28" | 26.75" | 16 | 1/2 - 13 |
| 1/2 | 23" | 25.5" | 24 3/8" | 12 | 1/2 - 13 |
| 1 | 20 1/8" | 21.75" | 20 7/8" | 12 | 7/16 - 14 |
| 2 | 17 5/8" | 19.25" | 18 3/8 | 12 | 3/8 - 16 |
| 3 | 16 1/8" | 17.75" | 16 7/8" | 12 | 3/8 - 16 |
| 4 | 14 1/4" | 15 7/8" | 15 | 12 | 3/8 - 16 |
| 5 | 12 3/8" | 14" | 13 1/8 | 8 | 3/8 - 16 |
| 6 | 10.5" | 12 1/8' | 11.25" | 8 | 3/8 - 16 |
| Flywheel | A | B | C | XG | Holes | Size |
|---|---|---|---|---|---|---|
| 21 | 23 | 26.5 | 25.25 | 0 | 12 | 5/8-11 |
| 18 | 19 5/8 | 22.5 | 21 3/8 | 5/8 | 6 | 5/8-11 |
| 16 | 18 1/8 | 20 3/8 | 19 1/4 | 5/8 | 8 | 1/2-13 |
| 14 | 16 3/8 | 18 3/8 | 17.25 | 1 | 8 | 1/2-13 |
| 11 1/2 | 12.375 | 13 7/8 | 13.125 | 1 9/16 | 8 | 3/8-16 |
| 10 | 10 7/8 | 12 3/8 | 11 5/8 | 2 1/8 | 8 | 3/8-16 |
| 8 | 8 7/8 | 10 3/8 | 9 5/8 | 2 7/16 | 6 | 3/8-16 |
| 7 1/2 | 8 1/8 | 9 1/2 | 8.75 | 1 3/16 | 8 | 5/16-18 |
| 6 1/2 | 7.25 | 8 1/2 | 7 7/8 | 1 3/16 | 6 | 5/16-18 |
| 17.75 D | 17.75 | 15.5 | 0.72 | 8 | 5/8-11 | |
| 15.50 D | 15.50 | 13 7/8 | 0.72 | 8 | 5/8-11 | |
| 12.75 D | 12.75 | 11 | 0 | 4 | 1/2-13 |
| Housing | Coupling | ECP3 | ECP28 | ECP32 | ECP34 | NPE32 |
|---|---|---|---|---|---|---|
| 6 | 6.5 7.5 | • • | ||||
| 5 | 6.5 7.5 8 | • • • | • • • | • • • |
||
| 4 | 6.5 7.5 8 10 11.5 | • • • • • | • • • • • | • • • • • |
||
| 3 | 8 10 11.5 | • • • | • • • | • • | • | • • • |
| 2 | 10 11.5 | • • | • • | |||
| 1 | 11.5 14 17.75 D | • • | • • • | |||
| 0 | 14 18 17.75 | |||||
| 00 |
Pulley Calculator
Here is a great resource for calculating pulley sizes, speed and belt lengths.
Wiring Connection Diagram
For most applications, an alternator with a 4-wire output (dedicated wiring) is the most efficient and least expensive. Another option is a 12-wire alternator. Twelve wire alternators can be reconfigured as shown in the wiring diagram below. There are terminals on the top of the alternator with labelled wires from the coils connected to them. You can reconfigure them by following the diagram to produce different results.
