[DeTomaso] Piston Ring Rotation.

Will Kooiman will.kooiman at gmail.com
Sun May 27 00:26:23 EDT 2012


The compression rings rotate all over the place as the piston moves up and down.

I'm not sure about the 2 oil rings.  If I remember correctly, my oil rings were notched to keep the gaps 180 degrees apart.  They were the only rings I've ever found like that, though.

I would reuse rings depending on the mileage.  If you use new compression rings, you need to have the proper cross hatch on the bores to allow them to break in properly.

On May 26, 2012, at 1:58 PM, Asa Jay Laughton wrote:

> Most of us are aware of the proper ring positioning when assembly an engine:
> http://www.351c.info/gallery2/d/218-1/ringspacing.jpg
> The two compression rings should be spaced about 30* (or about one inch) 
> from the front centerline of the piston, one on either side.  The oil 
> ring segments are the same on the opposite  side of the piston toward 
> the rear.  The illustration above shows this quite well.
> 
> But do the rings rotate after assembly?
> 
> A few years ago at the POCA Fun Rally, Jack had an expert who was 
> familiar with pistons.  He said indeed the rings do rotate, so in the 
> end it doesn't really matter where you index them to start with... 
> they're going to move.
> 
> Today I recorded the ring locations on my forensics engine.  I had been 
> careful not to turn the rings on the pistons when I removed the 
> pistons/rods from the engine previously.  Because I can't insure they 
> didn't move at all, the relationships below are rounded.  Here are the 
> results.  My "timing" is from the -front- of the engine, moving 
> clockwise.  The piston position at 12 o'clock is the part facing front, 
> the position at 6 o-clock is at the rear.
> 
> The first compression ring is at the top, the second on the bottom.
> 
> Piston    1st Comp    2nd Comp    Oil/Oil
> #1        8 o-clock   4 o-clock     4/2
> #2        10          11           12/3
> #3        10          2            10/1  (probably the only one closest 
> to installed)
> #4        8           8             8/8  (All ring gaps were lined up)
> 
> #5        9           2             5/5
> #6        12          9             5/5
> #7        5           4             6/5
> #8        9           3             3/7
> 
> As you can see, they are all over the place.  I'll work up a good 
> illustration and post it later.
> 
> Does this mean I won't index them the next time I assemble and engine?  
> Actually, I'll most likely still index them when assembling, only 
> because I'm anal about those things and I do believe spacing them does 
> assist with initial break in.  If they are spaced the same, I look at 
> that as an easy path for compression gasses to get past.  In other 
> words, gases might get past the lower tension oil ring segments and past 
> the gap in the bottom compression ring but then they'll have to travel 
> around the edge a while before they meet up with the gap in the upper 
> ring.  In the end, it may not really matter.
> 
> Asa Jay
> Pantera Research Institute, Pacific Northwest
> 
> -- 
> Asa Jay Laughton, MSgt, USAFR, Retired
> &  Shelley Marie
> Spokane, WA
> ******************************
> http://www.racingagainstautism.com
> http://www.teampanteraracing.com
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> 
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