Alex99

iTrader: (1)

Hi all,
I have some questions regarding the changes that GM introduced in 2004 for pistons and con rods.

Here is the official statement:
New for 2005: "The 5.7L LS1 and LS6 V-8s are equipped with new floating-pin pistons. First introduced on GM Powertrain’s Vortec 6000 H.0. V-8, these pistons feature wrist pins that “float” inside the rod bushing and the pin bores in the piston barrel. Previously, the LS1 and LS6 used a fixed-pin assembly, in which the connecting rod is fixed to the piston’s wrist pin, and the pin rotates in the pin bore. Snap rings now retain the wrist pin in the piston, while the rod moves laterally on a bushing around the pin. The floating pins were introduced as an interim change late in the 2004 model year."

I checked the part catalog and found out that the crankshaft has not changed - meaning that the crank's bobweights were unchanged despite the new pistons/rods.

I also know that the bushed rods are a little bit beefier that the pressed pin rods -
12607475 - LS2 (w/floating pin), LS3, LS4, LS6, LQ4/LQ9 (w/floating pin), 2004-05 LS1 (w/floating pin) - 1.41 lbs (639.565 grams)

12568734 - 1997-2003 LS1, 99-04 LQ4 with fixed pin (non-bushed) 1.36 lbs (616.886 grams)

Now I would like to understand if the weight of the new floating pistons is any different from the pressed piston weight (434g).

If the piston weight is the same I need some more education on balancing weight tolerances (20g+ for the bushed rods).
How good are the stock rotatting assemblies balanced and can they tolerate this much weight difference without any vibrations being noticed.

I'm in the process of replacing some stock pistons in my LS1 so I would like to know if I could move to the newer style pistons/ rods.

Thanks
Alex

chrisfrost

iTrader: (8)

Well 1 thing to note here is the fact that the pin diameter of the newer style rods/pistons is smaller by between .030 and .050" and I believe the compression height is a little different so if You do go this way You have to do both the rods and the pistons and also as far as the truck engines in 2007 they decreased the piston to bore clearence from .002" to .0007" . I'm not sure when the LS1's .....etc changed the piston to bore . As far as the crankshaft is concerned , I've been told that the bob-weights are heavier than they need to be so You can go with heavier rod/piston/pin/rings combo without any problems. Good luck

Alex99

iTrader: (1)

UPDATE:
I received the stock floating pistons and compared their weight against the early version.
With rings, pins and circlips the new pistons are 9grams lighter than the old ones.
This makes the bushed/floating piston-rod combo a little less heavier but its still about 15grams heavier than the stock piston-rod combo.
I will probably take some weight off the bushed rods but I would still like to understand how these 2004/2005 rotation assemblies look like in regards to balancing etc.
I talked to a engine shop owner yesterday and he said that the LS engines are very good balanced from the factory (within a few grams only). Can somebody confirm this?
Thanks
Alex

mark21742

Most of the time if not always you should have your rotating assy rebalanced when ever you change a part by have weight added or removed from the crank

1961ba427

iTrader: (26)

Kinda old thread...but a good read. Does anyone have any new info to add?