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

bill at antique-engines.com bill at antique-engines.com
Tue Apr 19 10:44:23 PDT 2005


Technical? Here ->

http://www.vtt.fi/inf/pdf/tiedotteet/2002/T2178.pdf

:-)

You can also think of the angles gap as a means of further restricting gas
escape. Although it's not really needed to any degree, it does offer SOME
improved sealing while allowing a larger gap.

You don't want the ring ends to line up over ports on a 2 stroker - they
can "catch" and cause problems with wear, etc. so most strokers are
pinned.
They also don't experience the same effects as rings in a 4 stroker
experience. There are differences in gas movements and pressures. So the
rings behave differently and wear differently.

I've also heard from old-timers (does Arnie fit that category?) that rings
were pinned early on due to the fear of gaps lining up. Pins were also
used for unscientific reasons in 4 stroke engines, so why continue if it
didn't make sense after later research showed it not needed? Pull the pins
and save production costs. They offer no improvement on a 4 stroke.

Bill

> Arnie and Bill,
> After digesting what both of you have written so well, you have helped
> me answered a question I have had for a long time. That is, why did the
> engine manufactures make the ring gaps with an approx. 45° angle instead
> of butt ends? Bearing in mind what you have both written, to solve the
> strange wear pattern that a pinned ring in conjunction with a butt end
> gap would create, the solution was to make the gap on a 45°. This
> assured the ring was wiping completely around the cylinder and would not
> leave an unworn ridge down the length of the cylinder. Seems kind of
> obvious now, but until I digested both of your points I had never put
> the pieces together enough to realize that one was a function of the
> other.
> Curt Holland
> Gastonia, NC
>
>
> Arnie Fero wrote:
>
>>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
>>>>
>>>>
>>
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>>
>>
>>
>
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