Bellhousings, or pump motor adapters, are a simple and accurate way to align an electric motor to a hydraulic pump. There are many ways to calculate the length of the bellhousing required and choosing the correct length is critical to your build. Adding the motor and pump shaft lengths together will not always guarantee your build will fit simply because while the electric motor shaft is generally longer than your coupling half, this does not always hold true for the pump shaft.

Once you have determined what electric motor, hydraulic pump, and coupling you are using you will need to know the following to find the minimum length of bellhousing required. Our values for this examples are in brackets ( )

mUse either the motor shaft length (c) or the coupling half length (g), whichever is longest.
Our motor shaft (c) is 5.00" and the coupling half (g) is 2.25"”" so we will use (c) 5.00".

nUse either the pump shaft length (d) or the coupling half length (g), whichever is longest.
Our pump shaft (d) is 1.68" and the coupling half (g) is 2.25" so we will use (c) 2.25".

pIf the coupling half OD (h) is larger than the pump pilot (b), you will need to add the pump plate thickness (f) instead of the pump pilet length (e).
Our coupling OD (h) is 4.00" and the pump pilot (b) is 5.00" so we will use the pump pilot length (e) of 0.50" instead of the pump pilot thickness (f) of 0.75".

The minimum length of the bellhousing required would then be
(m) + (n) + (p) + (j) + (k)
or
5.00” + 2.25” + 0.50” + 1/4” + 1/8” = 8.13”

In this example, we have determined we need a bellhousing for a 324TC Nema motor to an SAE C pump that has a minimum of 8.13” long. The closest standard bellhousing on the adjacent page is a 1429-3 that is 8.81” long. The difference between 8.81” and 8.13” (0.69”) must be able to be made up in either of the two coupling to shaft engagements as stated by your coupling manufacturer.