Let's talk pistons in an engine build

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clutchdust

Millionaire Playboy
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I know that piston manufacturers tend to put a notch or some other kind of indicator on the pistons representing where front is on a piston. If it's a two valve relief or domed, I totally get that it needs to be correctly oriented to the chamber. But let's say you have a brand new flat top, dished, or four-valve relief piston in a fresh motor. So long as the rod is oriented correctly on the crank, does it really matter which direction the piston is facing?
I just don't see how it does but I'm always willing to learn. If it does matter, please explain why.
 
clutchdust said:
I know that piston manufacturers tend to put a notch or some other kind of indicator on the pistons representing where front is on a piston. If it's a two valve relief or domed, I totally get that it needs to be correctly oriented to the chamber. But let's say you have a brand new flat top, dished, or four-valve relief piston in a fresh motor. So long as the rod is oriented correctly on the crank, does it really matter which direction the piston is facing?
I just don't see how it does but I'm always willing to learn. If it does matter, please explain why.
Click to expand...

If you put a flat top or dished piston with 2 valve reliefs in backwards you would end up with bent valves for sure. The you have a 2 valve relief piston with a intake pocket and exhaust pocket and these are considered left or rights and depending on the manufacture they go by either exhaust pocket or exhaust pocket for your left or right.

Most OEM replacement 4 valve relief pistons have wrist pins that are offset appox. .060 and if put in backwards would make for a noisy engine.
 
Didn't know about the offset. Makes sense now though.
But as long as we're on the subject of pistons, let me ask this. If the second ring isn't a true compression ring, what's it's purpose?
 
clutchdust said:
Didn't know about the offset. Makes sense now though.
But as long as we're on the subject of pistons, let me ask this. If the second ring isn't a true compression ring, what's it's purpose?
Click to expand...

It is a scraper ring and most are a tapered faced ring, If put in up side down it will burn oil.
 
IMO the 2nd ring functions as both a compression and a scraper ring, the top ring seals oiff for the most part but the 2nd one aids in this and also scrapes oil If it were a pure scraper ring it could be constructed like the actual scrapers.

Another thing the rings do is dissipate heat into the cylinder walls.
 
Twin_Turbo said:
IMO the 2nd ring functions as both a compression and a scraper ring, the top ring seals oiff for the most part but the 2nd one aids in this and also scrapes oil If it were a pure scraper ring it could be constructed like the actual scrapers.

Another thing the rings do is dissipate heat into the cylinder walls.
Click to expand...

How would a tapered ring work as a compression ring??? Been building engines for 35 plus years and never heard of anyone using a tapered compression ring.

That being said some of the tall deck GM truck engines use 4 piston rings 2 top rings are compression 3 is a scraper 4 is the oil control rings.
 
http://www.hastingsmfg.com/Race_Catalog_Pdfs/Piston_Ring_Functions.pdf

http://www.hotrod.com/techarticles/engine/hrdp_0910_piston_ring_tech/viewall.html

hrdp_0910_02_z%2bpiston_ring_tech%2b.jpg
 
my aircooled VW pistons had an arrow but I can't believe it really matters how you install them on this engine :lol:
:lol:
:lol:
 
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