2.0 Oil Ring

[304065]

Why is the oil scraper ring on the bottom of the piston skirt?

Why did they move it up under the compression rings for the 2.0T?

Why such a big piston skirt? Did this change occur when the "slipper skirt" was invented?

Inquiring minds want to know.

[304065]

One thing that occurs to me is that it's easier to install the cylinders with the rings at the top. With the oil ring at the bottom, the piston has to be all the way inside the cylinder, which makes it impossible to install the piston pin. With the rings at the top, you can compress all three, stick the piston partially into the cylinder, then mate the piston to the rod and slide the cylinder all the way on.

[jluetjen]

I donno John. I took a look in some of my books for an explanation, and while they can explain the 2ndary vibrations of a flat-plane V8 and the theory of oil-ring cross-section design, they don't explain that. I did notice that some of the 356's had pistons like that, as did the Maserati 250 engine and other pre-60's engines. But many didn't. I've rarely seen it in "modern" engines.

[304065]

Yep, it's definitely an old school concept. Here are some old MGA pistons, too.

[TimT]

John I noticed this thread dropping to the nether world of this BBS. I was hoping for a moment of clarity that would enable me to explain why they had those rings down there.

alas I cannot.

Then you post a pic of 5 ring pistons...

oh the humanity

Maybe chalk it up to ****ty machine practices and manufacturing tolerances

[304065]

Here is an interesting article which cites a book produced by Mahle.

http://www.babcox.com/editorial/ar/eb40354.htm

The reduction in number of rings and their width is intended to reduce friction, a good idea. As the rings get narrower, the piston is less able to tolerate bore distortion. . . do I hear water cooling?

[cstreit]

Interesting article, thanks John.

[304065]

356 Pistons