MonkeyManZ28

whats the diff between bushed & pressed pin connecting rods? i have floating wrist pin pistons which ones do i need?

my94blackz

I hope i dont get these 2 mixed up, u have floating pins which require bushed ends. Floating is supposed to be more stable in higher rpms.

rskrause

Some wrist pins are press fit into the small end of the connecting rod while others are a "free floating" loose fit. A bushing, in this context, refers to a bronze insert in the small end of the rod that is used with a floating wrist pin. A pressed pin simply means that the piston, wrist pin and connecting rod are assembled with a press. In essence, the pin can't move because of the interference fit in the connecting rod. Stock motors usually use press fit wrist pins.

Floating wrist pins are more suited for high performance use. There is additional clearance (~0.0005") between the pin and the pin bore which prevents galling under high load and temperature. But floating wrist pins require a pin lock to keep the pin in place. There are three commonly used pin lock systems. Tru-Arcs, Spiralocks or buttons. Pin buttons are the least common and, in most cases, they're only found on fuel and blown alcohol combinations. Tru-Arcs are basically circlips that can easily be installed with a pair of snap ring pliers. Spiralocks are another matter entirely. A Spiralock is basically a spiral clip that is "wound" into the retainer groove. It is almost impossible for a Spiralock to back out in a running engine, but it is also difficult to install or remove. Spiralocks are the system of choice for racing and high performance applications.

Rich Krause

Lars

Thanks Rich for going into that amount of detail man, I definately learnt a thing or two from your post.

At what level of engine modifying would you decide to use a floating wrist pin rather than a press fit wrist pin?

Johnny Ray

Great explanation!

Thanks Rich!

rskrause

You are most welcome, thanks for the thanks!

Any aftermarket performance rebuild should use floating wrist pins and bushed rod ends. No reason not to, AFAIK.

Rich