I have a connecting rod designed with a plain spherical roller bearing with both sides sealed with a shaft seal.  In the con rod I have a grease fitting for applying grease once the con rod is installed on to the crankshaft. normal amount is around 20 manual pumps.

My concern is that during greasing, the air trapped inside the conrod housing creates excess pressure and pushes the seal out of the housing.

Is there a way to remove the air pockets while the bearing is being greased?  Also is there a grease fitting available that will prevent excessive greasing?

Lever action grease guns are capable of thousands of psi.  The air doesn't create excess pressure; it just transmits what the grease gun applies, softly.  Consider using/ specifying a direct action grease gun; no lever.

As for removing the air, you could evacuate the grease reservoir prior to initial greasing.  It's probably simpler to provide a bleed; a second channel opposite the grease fitting, equipped with a plug that you loosen or remove while injecting grease, to vent air or old grease.

Instead of a plug you might consider a pressure relief valve. It is not idiot proof but it makes an attack on the system a little harder to achieve.
20 strokes on a lever hand pump is a lot of grease for a bearing system. As stated above normal hand operated grease pumps are capable of significant pressure so you might want to consider a lower pressure pump.

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