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4BT Conversions

Posted by Eric Rego on

Occasionally a question comes up regarding using a Cummins 4B four cylinder engine for a conversion.  In addition to having a shorter length, which places the engine a notable distance from the radiator, the other issue with 4 cylinder engines is engine vibration.  Inline four-cylinder engines have an inherent vibration that occurs every half crank revolution and attempts to shake the engine up and down. This is known as a second order vibration that originates from the fact that the rate of acceleration and deceleration of a piston when it is near top dead center is different than the acceleration and deceleration of a piston at bottom dead center. 

 

When a four cylinder engine is soft mounted using rubber engine mounts, this vibration can be isolated from the chassis.  Because Oliver and White engines are hard mounted, a special balancer is required to counteract the resultant shaking forces created by four cylinder engines.  On a 4B Cummins, this balancer mounts to the main bearing caps and is driven by the crankshaft timing gear.  Because of the bulk of the balancer assembly, the number of pan options becomes limited.  In my experience, finding a 4BT with a balancer shaft installed from the factory can be challenging due to the majority of 4BT applications being soft mounted and hence not requiring a balancer.  If purchasing a new balancer, expect the assembly to cost well over $1000.


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