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CARRILLO'S FORCE FEED WRIST PIN OILING ("EDM-ing")
Force-feed oiling from the big end to the wrist pin end of the connecting rod is a process Carrillo Industries has employed since the mid 60's. This process was common practice in most Offenhauser Indy and Cosworth engines of that era. It was popular in those applications due to the very high top end heat developed as a result of turbo charging. The oil directed at the pin end allows for better heat dissipation and lubrication.

With the advent of significant crankcase vacuums, baffling, and windage efforts, oil has become a scarce commodity at the top of the cylinder bore. This problem was presented to us, and we suggested the implementation of top end oiling. As a result, the popularity of force-feed oiling of the top end has increased dramatically.

Carrillo Industries has done a significant amount of testing and evaluation in the last thirty years relative to force-feed oiling. The process, although simple in description, is actually very critical and process sensitive. Needless to say, the simplest way to produce a hole from top to bottom of the connecting rod would be to deep hole or "gun drill" the hole. The difficulty with this method is the finish within the hole. If a stress riser or surface defect is left in the hole, it can easily lead to a fracture and eventually a failure. We employ substantial preparation for the hole prior to electronically disintegrating the material (EDM). This process leaves a much more consistent finish. After the hole is installed, we subject the part to normalization and heat treat to further stabilize the stresses generated. The part is then carefully deburred and inspected before finish procedures. Note that the dimensions of the part are specifically designed to accept the hole without compromise.

Now to address the effects of the force-feed. This process is not designed for all applications. The engine systems must have adequate and constant oil flow to support the oil going through the connecting rod. Further, it is not practical to assume that the oil supplied to the wrist pin area is constant. It is impossible for the oil supply to the top end to overcome the reciprocating effort of the connecting rod and piston assembly. A conclusion is that the oil hole and the slot behind the bearing become a reservoir for oil. As the connecting rod reciprocates downward, oil in the "reservoir" will gravitate upward to the wrist pin bore. The net result in our opinion is that force-feed oiling will help to inhibit problems at this piston and pin, but certainly, it is not a complete and absolute solution to all problems in that area.

The engine builder and/or designer must conclude if the force-feed oiling of the pin end will contribute to the durability and longevity of the specific system.

Regards,
Fred Carrillo and Jack Sparks
CARRILLO INDUSTRIES