One of the main problems with small compression height pistons is when the pin boss gets into the oil ring groove. Look at the above pictures, you'll see that a lot of the oil ring support is eaten by the pin boss. That requires the use of oil ring support rails to keep the oil ring from fluttering and having problems with oil control. Piston rock hurts rings and cylinder sealing, but pin placement alone is a minor factor in causing piston rock.

Piston rock is encountered in some setups with short CH. However, it's not really the pin location itself that causes piston rock. The combination of larger skirt-to-wall clearance, shorter skirt length and a big stroke crank with short rods in a short deck block really aggravate piston rock.

Sure, some pistons have offset pins to keep the piston loaded on the thrust side to reduce the rattle on TDC/BDC transition. Any given piston design could do that no matter what the CH.

 

I guess this is something I will need to understand piston by piston, and it was exactly the feedback I was looking for. Thank you.

Again, I totally agree here. I guess my concern would be the same. I also think that it tends to be a larger part of the longer stroke and more extreme angles... but what I am really trying to figure out is how much of that effect can be contributed to stroke/rod angles and how much the higher pin height.

Looks like I'm going to be calling a few piston manufacturers...

 

Here's one from the tractor. I honestly never paid attention to how low the oil tings were. It does take 22 qts of oil to fill and blows out 2 qts per run.

 

my thoughts the closer pin to the top helps take stress off rings .allowing you to use thinner compression rings & shorter skirt pistons. but the offset is oil rings being close the pin with out the support of piston cause them to flex and the heat from pin is there. alot pistons rings come extra oil scraper. to go on the bottom oil ring for support, example at beging of post same stroke & same rod length just different c.h.//// let say a 5 gallon bucket is piston .take 1 bucket and run a rod through it (representing piston pin) take another and run rod through it but closer to the open in of bucket representing a different c.h. now take grab the rod (piston pin) with each hand (arm representing connecting rod) .lift over your head.bet you can control the one at bottom bucket better.just my 2 cents

 

Yea you can control it better... But does having the pin so close to the rings actually end up putting more force on them against cyl walls? Concentrate that force in a way.

The other thing to consider is that i think the LSA and LS9 have a lower pin height than the rest of the LS engine family

 

I do, But I'm not telling...






































JFWY....


There are a few things that have to be taken into account that determine were the pin ends up on a piston in a stroker application.

1. Deck Height in relation to crank center line.
2. Effective Cylinder length.
3. Available rod lengths for a given application.

A piston Will have an Approximate length for any given application. They usually like to make sure the Lower oil ring and the wrist Pin stays Approx. X amount above the bottom of the cylinder. This ensures you don't launch it out the side of the block should you have a short cylinder. You also can only bring the side skirt's so far down out of the hole before you lose support and put excessive stress on it.

Remember a Piston is not a true cylindrical shape from top to bottom. The bottom is always bigger toward the bottom of the skirt.