[SEL] Re: Pinned Rings - Problems or Not?

[Arnie Fero]

Hi Bill,

Allow me to offer up a technical term on this line of reasoning.
Bullshit.

The problem with the two examples offered; namely a wristpin that pokes
out and wears a groove in the cylinder wall and a stuck piston ring
producing abnormal cylinder wall wear, is that neither one represents what
happens with normal pinned piston rings.

A normal ring makes contact uniformly with the piston wall and the oil
film based on the amount of "spring" that the ring has.  A stuck ring
can't move away from the wall, neither can the wristpin.

My 4 hp Robertsonville (a 4-stroke engine) has pinned rings.
Take a look at...
http://www.oldengine.org/members/arnie/Piston_Rings/rings_1.jpg
http://www.oldengine.org/members/arnie/Piston_Rings/rings_2.jpg
http://www.oldengine.org/members/arnie/Piston_Rings/worn_rings.jpg

As you can clearly see the rings are BADLY worn (not stuck).  The cylinder
wall had no indications whatsoever of any abnormality caused by the "ring
ends" even though the rings are pinned.  BTW I kept the pins when I
replaced the rings.

My two cycle Bessemer half-breed also has pinned rings, a lot of ring and
cylinder wear and no indication whatsoever of "ring end" effects.

Engine builders dropped the idea of pinned rings in 4-stroke engines for
one reason only.  The added cost was not offset by any performance
improvement.  Not because it caused problems.  We obviously don't see
problems in our two-stroke engines with pinned rings.

See ya,  Arnie

Arnie Fero
Pittsburgh, PA
fero_ah at city-net.com

On Fri, 15 Apr 2005 bill at antique-engines.com wrote:

> You'll wear a ridge where the ring gap is.
> http://www.sacskyranch.com/piston_ring_rotation.htm
>
> One way to show rotation is to disassemble an automotive engine - and look
> at the spot where the top ring lands in the cylinder at each TDC - if
> there was no rotation, you should see where the ring end gap left an
> unworn area in the cylinder, but you won't unless the rings were stuck.
> It's worn all the way around.
>
> > bill at antique-engines.com wrote:
> >
> >>On a 4 stroker it's normal and preferred.
> >>
> > Please elaborate. Why is ring rotation preferred as opposed to being
> > pinned in place?
> > Curt