Piston wrist pin...floating vs pressed question

[Warren F.]

I keep reading that the advantage of floating pins versus pressed is ease of assembly/disassembly.

For some reason, my thoughts are that a floating wrist pin piston assembly would allow the piston to travel in the cylinder bore more straight(not sure this is the right term to use) and have less side thrust or wear to the side of a cylinder from the ineria?

I guess I'm looking for a method to alleviate cylinder wear using my original GM components and not wear out my standard bore block.

[Duke W.]

Re: Piston wrist pin...floating vs pressed questio

Ease of disassembly/assembly is the ONLY difference. There is absolutely NO difference in piston geometry or side loading for the same crank throw and rod length. There are arguments that floating pins reduce internal friction, but these only apply to racing engines that spend most of their lives at high revs.

Contrary to myth, piston side loading due to rod angularity does not wear cylinders. Any measureable wear is almost always at the very top of the bore where the rings reverse and there is no hydrodyamic lubrication at the ring/wall interface. At the point of maximum side, load piston skirts enjoy full hydrodynamic lubrication, but cylinder walls at mid bore are subject to scoring if any particles larger than about 20 microns get trapped between the skirt and wall.

Floating pins also require attention to lubrication at the rod bushing and attention to tight radial clearance/tolerance in the rod bushing and end play clearance/tolerance in the piston. Otherwise they won't last.

If you are restoring an engine that you expect to last as least as long as OE engines, it is not worth the cost/risk to "convert" to floating pins relative to the one-time cost of a machine shop assembling the pistons/rods using proper tools and fixtures for pressed pins.

Duke

[Warren F.]

Thank you for the EXCELLENT explanation. Duke *NM*

[Clem Z.]

make sure the rods are aligned to prevent

side thrust of the pistons and if the shop does not know what you are talking about,run don't walk

[Warren F.]

Sound advice as well, Clem. Thank you. *NM*

[Joe L.]

Re: Piston wrist pin...floating vs pressed questio

Warren-----

I agree with Duke and clem. Also, with the floating pin design, retainers must be used to secure the piston pins and prevent them from contacting the cylinder walls. These retainers can be problematic. The "teflon button" type are probably the least likely to fail, but may not have the long-term durability required for a street engine. I would NEVER, EVER use floating pins in a street engine. Virtually nothing to gain and a lot to lose.

That I know of, GM has not used a floating pin design in a PRODUCTION engine since 1969. That year, the floating pin design was used for the L-88 and 302 Camaro. Afterwards, no floating pin design was used again. It is possible that some of the very current engines like the LS-7 and the 3.6L V-6 MAY use a floating pin design. I'm not sure as I have not researched those details of the engines.

[Clem Z.]

Re: Piston wrist pin...floating vs pressed questio

yes the latest corvette engines not just the ZO-6 use full floating wrist pins. several years ago i witness a dyno durability test up at the corvette engine factory where they were running the full floating wrist pins.they were doing this to eliminate piston "slap" and to get better fuel milage by reducing the friction. must have worked as GM now uses it.

[Clem Z.]

the best system to prevent the retainers from

being dislodged is to use wrist pins with a bevel machined on the outside diameter ends of the pins and the use of a round wire retainer. this system,because of the bevel,causes the round wire retainer to be pressed outward into the groove in the pistone as the pin presses against the retainer. we used double snap rings and spirial locks but the best system is the round wire retainer because of what i posted above. the double snap rings must be installed with the sharp edges towards the pin and the outer one the sharp edge towards the outside of the piston. this is because if you look at a snap ring you will see one side has a sharp outside edge and one side the edge is rounded because of the stamping method used to manufacture them

[Bryan L.]

Re: Piston wrist pin...floating vs pressed questio

Piston slap and the ticking of the solid lifters IMO made the 302 one of the best sounding SB engines ever. I love the sound of a 302 in the morning.

BL

[Clem Z.]

Re: Piston wrist pin...floating vs pressed questio

the piston slap was because of the forged pistons that required extra piston to wall clearance. now days no one wants a noisey engine on start up just ask GM about the problems they had with the LS series engines making noise on start up. there were even lawsuits over this