Date: Mon, 11 Oct 2004 09:03:19 -0700
Reply-To: Mark Keller <kelphoto@SHAW.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mark Keller <kelphoto@SHAW.CA>
Subject: Re: Safe 2.1/1.9 Rpm: survey/query
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I throw in my bit here too.
I brought up the issue engine durability and high rpm's vs piston ring
harmonic resonance a while back. Apparently when piston rings slide up
and down the cylinder walls beyond a certain speed i.e. feet per min, I
believe the criteria worked out that our 3" stroke engines reach this at
just over 4000 RPM, conditions begin to be conducive for ring resonance.
The Green arc on our tachs stop here, with a hashed green area up to
4400 Rpm., as "temporary operation" range.
When Bob Donalds speaks of not re-using old pistons when
reconditioning the engine, becasue the rings lands are always worn,
this is where damage from harmonic resonance shows up. One listee
wrote the list with a testimonal that he suffered engine problems,
right after a 4600 something Rpm Test Run and that tear down revealed
damaged ring lands. Abeit the last run was probably the "last straw
which broke the camel's back."
Piston rings do resonate at some velocity. Personally the RPM onset of
ring resonace is probably dependent: on milage, wear on the engine,
which piston and ring combo, cyclinder wall condition and etc. . My
feeling is that operation above the 4000 - 4400 range and up for
continued operation is incompatible with engine longivity. How long is
too long? Well condition and quality of your engine are the main
variables, The more miles on the motor, the less I'd be tempted to push
past the 4400 RPM limit for very long, remembering our camel example
above, and not knowing the PO's driving habits!
Another listee Frank Grunthaur(sp) wrote back on this topic, that
manufactures had devised a way to control piston ring resonance, with
some trade offs. If you were build an engine to rev high, I guess
4000-6000 rpm, lower tension rings could be used, but cylinder sealing
at lower RPM suffered-- something to that effect.
Piston Ring resonace damage is a real issue of a cumulative nature.
Testimonials from owners of VWs inline engines suggest that they run at
RPM above our limits for a lifetime of use without issue. Perhaps, and
not a reason for me consider a swap, but if you have a inline engine,
then go with the high rpm rating VW gives for inlines. For my peace of
mind, comments like Bob Mcdonalds, piston ring land wear, VW's "Green
Zone" on the tachometer, and the knowledge that piston ring resonance is
lurking in the high rpm range, lead me to believe my engine's durability
in enhanced by venturing above the limits only when needed.
Mark Keller
91 Carat
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