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I'm curious as to why both 4- and 5-ring pistons are offered (by
Moss). Does it vary by year or model, or just builder preference? As
far as I can tell, cars came from the factory with 4 ring pistons.<br>
<br>
FWIW, I have a DWM 3-ring Omega set in my BJ8, and I haven't noticed
any piston slap.<br>
<br>
Bob<br>
<br>
<div class="moz-cite-prefix">On 4/19/2021 5:14 AM, m.g.sharp--- via
Healeys wrote:<br>
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cite="mid:002001d73515$86b4f330$941ed990$@sympatico.ca">
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<p class="MsoNormal"><span lang="EN-US">Many thanks to everyone
who responded to my question about the rings. Seems that
there are examples of people fitting that fifth ring and
leaving it off, and no-one reported a problem or bad
experience either way. It also seems there is no hard
knowledge on why that bottom ring was fitted, but several of
us, me included, think it may have been aesthetic: simply to
reduce the noise from piston slap. I thought Earl’s
response was most telling in that he had been through a
complete engine cycle (i.e. he is on his second rebuild
after 140,000 miles on the first) with a 5-ring piston and
there were no issues noted on the strip-down and good
performance.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">While I have no doubt
that extra ring may result in extra friction and rob the
engine of a horsepower or two, no-one has measured it, so we
do not know if that is significant in any way. The only
other potential down-side is that the bottom ring will
scrape the oil from the cylinder wall on the down-stroke,
reducing lubrication on any piston-cylinder wall contact
between the two oil control rings. However, the bottom ring
may also prevent the piston from making contact with wall,
or at least <u>reduce</u> the friction, so maybe that is
not an issue.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">My goal is a well-built,
reliable, original car with factory-level performance.
Given that, and some concerns about the unknown consequences
of an empty ring groove, I am electing to install the 5<sup>th</sup>
ring. Also, I think there is wisdom in Hank’s comment that
as a general rule parts should be installed as the
manufacturer intended – who are we to second guess the
engineers who thought it necessary to add that ring?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Interesting discussion,
and if anyone ever turns up hard engineering evidence as to
why that extra ring was added, I would be very happy if they
would share it.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">As always, this list is
amazing for providing a forum for providing a forum for
discussion on the things we find interesting – as arcane
they may be!<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">With thanks, Mirek<o:p></o:p></span></p>
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