[DeTomaso] Piston Ring Rotation.

jtaphorn at kingwoodcable.com jtaphorn at kingwoodcable.com
Sat May 26 22:46:43 EDT 2012


This raises a question.  My previous research on engine rebuilding had authors consistent with the warning to not reuse engine rings.  This was championed even if the engine was being rebuilt after very low mileage.  I've interpreted the advice as being once a piston is removed from the bore, new rings are required.  I had always assumed it was because you would never be able to get the rings back in alignment.

So, is there another reason why rings shouldn't be reused or is it all a ruse by ring manufacturers to sell more rings.

I've had to pull pistons on several very low mileage engines for other issues.  Perhaps, I should have reused the rings.

JT 
---- Asa Jay Laughton <asajay at asajay.com> wrote: 

=============
I've created an illustration of the piston compression ring gaps on the 
disassembly of my old Mach I engine.

http://www.teampanteraracing.com/index.php?option=com_g2bridge&view=gallery&Itemid=57&g2_itemId=4970

In that same gallery I've posted a few photos of the main bearings and 
other wear.

Asa Jay

Asa Jay Laughton, MSgt, USAFR, Retired
&  Shelley Marie
Spokane, WA
******************************
http://www.racingagainstautism.com
http://www.teampanteraracing.com
http://facebook.com/racingagainstautism


On 5/26/2012 11:58 AM, 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
>
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