When rebuilding an engine, often the existing starter on the engine may not have enough cranking power to adequately turn the engine over during starting. This is especially true if the engine compression ratio has been increased or if the engine has been changed to produce more horsepower and torque.
To get more torque during starting, often gear reduction starters are used. When installing such a starter, it is important to check the starter pinion to ring gear clearance. This clearance is shown in the drawing below. Depending upon starter manufacturer, this clearance is often stated as 1/16 inches, or as .100 inches, plus or minus .040 inches. This clearance will be different for different engines and starters. When you buy a new gear reduction starter, make sure you know the correct clearance. If the clearance is too small, the ring gear may scrape on the pinion gear. This may happen during heavy acceleration or when the transmission is put in reverse. It all depends upon the clearance between the two gears.
In order to check the clearance, remove the dust cover on the transmission. Then look upward to see the clearance when the engine is not running. Use a feeler gauge to check the clearance. To change the clearance, shims are used to position the starter pinion gear farther away from the ring gear. Refer again to the drawing. This shows the location of the shim. On this particular starter, the shim is placed between the bearing and the seal. In order to install the shim, the starter should be removed from the engine and the nose assembly should be removed. The shim is then put in place to produce the necessary clearance. Note that different engines and different starter manufacturers will have different procedures and clearance specifications to install the shim. Always follow the manufacturer's suggested procedures.