I am rebuilding an ls4 for a swap into my 88 fiero and have a question. The engine is in very good shape but it is torn down. I have noticed the piston skirts are scuffed considerably more on the outside/lower side/gravity side than the inside. Good old piston slap I presume. I am at the point where I am ready to reinstall the pistons and was wondering if I could swap sides so the outside had the less wear side of the coating. These are the stock flat top pistons and the rods were not removed from teardown. Is swapping the sides possible or will it mess up the dynamic balance of the crank/assembly?

My experience (and how I was taught decades ago) is that you always return worn parts (pistons, lifters, etc) to their original locations. The reason being that there will be accelerated wear on the "new" surfaces (if relocated) and the end result will be more wear overall. I'm curious what others will say.

The dots on the pistons & the flat flange of the connecting rods face towards the front of the engine.
The piston pin is offset to reduce piston slap noise.

I would not attempt to install them backwards.
If you are concerned with skirt wear, buy new pistons.

The short answer is no, you cannot but technically you can but the engine will experience more piston slap and loss of power from low to mid range. Fuel economy will go down and you 'll be embarrased to be smoked by a 2006 Toyota Prius off the line. And this is why.
All stock engines have a measure of piston pin offset which is there to put the piston OFF squared with the bore properly before the power stroke starts. If you swap the piston around when the piston goes up it will not be properly OFF squared, it'll be squared and a more severe piston slap will resulting in even more wear and/or braking the lower piston skirts due to severe slap. That's what happens mechanically, as far as performance if you flip or turn around that offset you are reducing the displacement of the engine causing the engine to end up with less power, drivability issues, noises that can be picked up by the knock sensor to make things even worst. Just get new pistons and re hone the cylinders. If you want to understand the explanation above watch my video on Piston Pin Offset.
According to your piston wear description the problem was lack of lubrication, so make sure you investigate before you re assemble.

https://youtu.be/3QRPEMMQoH...AMOcPmd1fjB0wDxu&t=3

Thanks for the input fellas. To clarify, what I was thinking was swapping the right bank pistons with the left. The dots/dimples on the tops would still be facing the front.

What I have noticed is that the skirts on the outsides/lower sides of the pistons are worn more than the skirts on insides/top sides. Would that be gravity causing that? Swapping banks would put the perceived more worn sides to the top side which appears to not get as much wear as well as it would put the side with the least worn coating on the lower sides which are perceived as a experiencing more wear.

I don't think piston pin offset would be a factor as the top dots/dimples would still be facing forward. Also for this motor there are not left or right bank specific pistons, they are all the same.

Also, the rebuild consists of new bearings, rings, bolts and seals all throughout.

Anyhow, I have inspected the pistons closer and the additional wear the outsides/lower sides have is not really that much to worry about. The main thing I was concerned about swapping banks was the balance. But, I'm not gonna chance it. So I went ahead and installed them the way they came out.

Thanks for the input!

Each rod has a smooth side (planned to rub against its adjacent rod) and a rounded side (due to the fillet on the crank journal). Swapping them in that manner would be worse than just flipping then 180 while switching sides.

That's a good point, swapping sides would reverse the rod sides like you say and not be good. I would have had to just swap the pistons and keep the rods the same place. Too much to mess with for a little OCD observation.

Changing my topic... what's your take on opening up the bottleneck on the stock ls4 intake? Ls2 and ls6 intakes are getting far and few in between and too expensive. I want to say I saw where someone cut out that oil pressure sending unit dent in the stock ls4 intake and patched it up, opening up the bottle neck. Of course they had no Richard Holdener type before and after numbers though. Wonder if that spot IS the main reason the ls4 intake is the worst?

Too bad the NNBS/TBSS intake looks like crap. Let alone it probably wouldn't fit under the fiero hatch anyway, they are getting quite plentiful.

[This message has been edited by BHall71 (edited 11-26-2024).]

quote Originally posted by BHall71: That's a good point, swapping sides would reverse the rod sides like you say and not be good. I would have had to just swap the pistons and keep the rods the same place. Too much to mess with for a little OCD observation. Changing my topic... what's your take on opening up the bottleneck on the stock ls4 intake? Ls2 and ls6 intakes are getting far and few in between and too expensive. I want to say I saw where someone cut out that oil pressure sending unit dent in the stock ls4 intake and patched it up, opening up the bottle neck. Of course they had no Richard Holdener type before and after numbers though. Wonder if that spot IS the main reason the ls4 intake is the worst? Too bad the NNBS/TBSS intake looks like crap. Let alone it probably wouldn't fit under the fiero hatch anyway, they are getting quite plentiful.

The LS4 intake neck is an issue, as well as overall plenum volume. You might try to heat up the indent and see if you can push it out some from the inside. Beyond that, even the original LS1 intake would be an upgrade from the LS4. Here is a Dorman LS2 intake for $500
https://www.ebay.com/itm/25...UCyatbcgWJFDAIxcFD9U ZFMIiS0J%2F%2BPQGCz%2Bv9Vj1bIdS4PTrb3r0Mk4JfwuTTcKMg35z6wYv9HnJYABBW6XXKqnU40jJK%2BOwui67cPnuiW6xLQVKMXetX3zBZgxeSefgrhPCpv%2F%2BzzWZdGMefcH%2Bik7TfATNOGUbSHkh5UAnfTTNATJsJdWda3THN8m0MKux0JX1QI0kZZ1rDg3ahV4Mi6H61v06x%2FcUF8o3OgC4ITpBy8qqN8MDiGit%2B10CFYaeg %3D%3D%7Ctkp%3ABk9SR5SL-LXtZA