Minimum Cruise 2300 RPM

[Colonel]

Feel free to shit on me from a great height as per usual, but
think very carefully before you cruise your direct-drive Lycoming
or Continental at less than 2300 RPM, [b]if your crankshaft has
counter-weights[/b].

I know that people love to drink the Kool-Aid of over-square
and lean of peak - no judgement.

However, highly destructive resonant vibrations can be very difficult
to detect until it is too late, and the damage is done.  Ask anyone
that makes a gear reduction unit.

Shit away.

[digits]

How can you know if your crankshaft has counterweights? Is that an internal thing linked to the engine model/serial nr, or is that something you can see externally?

[John Swallow]

Knowing nothing about counterweights, I googled...


https://mechanicsupport.blogspot.com/20 ... io520.html


I would hazard a guess that the engine manual should have info on that sort of thing?

[Colonel]

I have never seen a six cylinder Lyc or TCM without a counterweighted
crankshaft, but I'm sure someone will pipe up immediately with an
obscure example.

Most four cylinder Lycomings do NOT have crankshaft counterweights,
but some (notably fuel injected) variants do - you can tell by the alphabet
soup in the engine model number.

I used to fly a Mooney M20J - a fire-breathing dragon - with an angle
valve 200hp Lyc IO-360-A3B6D where the "6" as the fourth letter of
the model indicated counterweights.  You really don't want to know
what the "D" suffix indicated.

[Nark1]

Thanks Andy.  I usually cruise at 2250 or so.  I’ll bump it up a little.

[Slick Goodlin]

[quote author=Colonel Sanders link=topic=9071.msg24829#msg24829 date=1537660151]
You really don't want to know what the "D" suffix indicated.
[/quote]
Is it for the goofy double mag?

[Colonel]

(shudder) yes.

[url=http://www.tcmlink.com/pdf2/CSB09-11A.pdf]http://www.tcmlink.com/pdf2/CSB09-11A.pdf[/url]

and [i]twenty-seven[/i] Lyc 540 crankshaft failures at 2200 RPM:

[img][/img]

[Blakey]

Very interesting.  This Service Bulletin was released more than 7 years ago and this is the first I have heard of it.  My ignorance continues to astound me!

I note that the only non-injected O-470 listed is the O-470G.  Does anyone know if the "J" through "R" models found in 180s and other aircraft are exempt from this problem or is the list just incomplete.  I don't operate down in that RPM band with a high MP the description in the SB makes me nervous about even getting close to that.  I like my windows in my cabin, not in my crankcase!

[Colonel]

Yeah, I know that's kind of weird.  Is it a legal difference,
or an engineering difference, between the models of engines?

The problem with counter-weights misbehaving:

1) no one knows what they are
2) no one knows if they have them
3) no one knows if they are unhappy

until their crankshaft fails.

[David MacRay]

Yeah, I should probably put this on a t-shirt or hat.[quote author=Blakey link=topic=9071.msg24879#msg24879 date=1537897131]
  My ignorance continues to astound me!
[/quote]