I need some explanation about the definitions pressed pin and bushed pin.
If these definitions are referred to the rod configuration all is clear for me.
I don’t understand when this definition is referred as an attribute of the piston.
My L98 is in pieces, so I can see:
- Rods are PRESSED PIN , the pin is pressed in the small end of the rod, so in this configuration the rod and the wrist pin are like a single fix thing.
- The wrist pin hole in the piston has a dimeter a bit oversized than the pin pressed in the rod. Whit the combo (rod and piston) on my hands the piston is free to float on the pin (from left to right, from right to left and around it).
With the combo installed, with the piston inserted in the cylinder liner, the only free travel is that the piston can follow the different degree position of the rod.
I assume that the standard configuration (for a ’90) is PRESED PIN for the ROD and FLOATING PIN for the piston.
I’m wrong ?, I’m right?.
Searching for pistons, to buy for my L98 rebuild, and assuming that I buy Pressed Pin rods (like standard) I see that many piston brands have the definition about the pin (pressed or floating). This definition is refered to to the piston or to the rod configuration?
What’s about pistons with pin with wrist pin keepers (KB Silv’Olite)? This configuration allow the rotatioonal travel arount the pin but NOT the linear travel (the keepers are the end of the travel). They need bushed pin rods or they can be applied to pressed pin rods also? I think that this kind of piston can be applied to both configuration of rods. An example is my fully modified Harley Davidson with forged JE pistons and standard equipment bushed pin rods.(All HD pistons from Wiseco to JE to KB … Ross … Arias.. to stock cast one are with wrist pin keepers). In case of pressed pin rod, the pin must be pressed in the small end of the rod (in the center!) with an accuracy very very high to evitate (in case of low accuracy) an high stress to one side of the piston on the cylinder wall.
If I want to install KB pistons (with wrist pin keepers) in my corvette, the best solution is the Bushed pin Rods??
Another question: The pin diameter is allways the same on all piston kit?? Or there is the serious risk to buy a pressed pin rod set where the small end hole is bigger or smaller referred to the wrist pin diameter???
An advise and an explanation is wellcome.

I know… too many questions!!!!…I’m sorry for my English language, and I hope you understand my question.
TIA
Beppe - Italy



[Modified by conv90, 9:54 AM 6/7/2002]

 

First - your English is not bad at all - don't feel sorry.

Piston pins - when buying pistons the pin configuration is stated as a match to the rod. Normally it is specified as press-fit or floating-fit. And yes, it refers to how the pin fits the rod.

All that I have seen have floating pins in the piston, IE the pins are always free to move in the piston. Normally it is pretty easy to tell what setup a piston is for, if has pin retaining clips - setup for floating-fit rods, if has no pin retaining clips - setup for press-fit pin rods.

And yes, the 90 would be factory press-fit rods.

Tom Melton
82 CE
86 Z51 Coupe

 

You are on the right track.

A pistion that is set up for floating pins (i.e. has pin retaining rings and
grooves) can be used with either press fit or bushed (floating) rods.
However, if you use them with press fit rods, DO NOT install the pin
retaining rings. The rod (and therefore the pin in the case of a press
fit) has to be able to move back and forth a bit.

Pistions that do not have grooves for retaining rings can only be used
with press fit rods.

Good luck - Dan