Flypast111

This discussion is about piston wrist pins, specifically. From 1999-2004, GM LS engines primarily used "PRESS-FIT" piston wrist pins. Here are some details about this application (based on hand-caliper measurements);

NOTES (1): GM 1999-04 4.8L/5.3L PRESSED-PIN Connecting Rods (PNs 12568736&34 - 4.8L/5.3L)

Connecting Rod PRESSED-PIN Small End (NO bushing) => Width x Thickness => 0.940in. x 0.160in.

ROD ID = 0.94350 +/- 0.00040 => range (0.9431-0.9439)

WRIST PIN OD = 0.94475 +/- 0.00005 => range (0.9447-0.9448)

Max. Interference = 0.9448-0.9431 = 0.0017 in. (high - about 35k+ psi stress or 5500+ lbs load)

Min. Interference = 0.9447-0.9439 = 0.0008 in. (low - about half of max. condition above)

Rod-Pin Clamp Load = Important >> STRESS RELAXATION >> Rod-Pin joint compressive stress will decrease via mechanical-thermal-cycle material stress relaxation during "life-cycle" operation => ultimately, some REDUCED/RELAXED clamp-load will become the actual/long-duration material stable condition


As for the "FLOATING PIN" applications (2005-2014 and more), we have the following;

a) the connecting rod wrist pin bushing is typically a "steel-backed bronze" material that is lite-hone machined to set-floating to piston pin od

b) sample bushing part numbers are given as; Clevite 77 223-3663 / Sealed Power 4514Y / Enginetech EB023 plus more

c) bushing geometry is approximately; Length = 0.919-0.922 in. (width of rod) / OD = 1.030 in. / ID = 0.920-0.925 in. (unfinished - requires fitment)

d) utilizing the GM connecting rod and Silv-O-Lite piston parts given below, we have an example of this FLOATING PIN geometry

NOTES (2): GM 2005-14 4.8L/5.3L FLOATING-PIN Connecting Rods (PNs 12607478 (4.8L) & 12607475/12649190 (5.3L))
Silv-O-Lite Piston 3499HC::>> Published Pin OD >>range 0.9429-0.9431 in.
[Hand-Caliper Measurements]>> Measured Pin OD >>range 0.941-0.943 in.
>> Measured Pin Bore ID >>range 0.945-0.946 in. (set-floating to pin od)

GM 12607475 Rod (refurbished)::>> GKN 3847-335-221 Cracked Powder Metal
>> SNs:: Rod=189 & Cap=262 (machine dent-print)
BUSHED ROD ID =range 0.944-0.947 in. >> 0.9455 +/- 0.0015
(very visible lite-hone finish machining - set-floating to pin od)

Piston-Pin-Rod Assembly::Slip-Fit with "slight sensible-play" movement (piston-to-rod)
(steel-backed bronze bushing plus lite-hone machining to fit assembly)

Generally, the floating pin geometry has become the current practice for GM LS engine applications (2010 and up). It is noted that many high performance engines of current usage are also utilizing floating-pin geometry. Clearly, the material condition required for press-fit wrist pins has become a point of discussion and concern for manufacturing quality control, performance and durability. So, which do YOU choose - both are available for many applications.