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Transmission rotor rpm cable and dual tach

Service and maintenance tips, questions, and issues.

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Transmission rotor rpm cable and dual tach

Postby seneca2e » Sun Jan 06, 2013 9:07 am

Well despite cleaning and lubing the rotor rpm cable my tach keeps bouncing around plus when they "marry" up there is about a 100 rpm gap between them. The engine tach is correct since when it reads 2900 rpm I shot the main rotor speed with a very accurate tach checker aimed upward thru the blades and it read 472 rpm-right on the money! The rotor rpm reads above the redline erroneously. So I think that gauge is gonna have to come out for an overhaul and sync(about $500). Probably get the MP gauge diaphragm done if I have to be down at the same time($225). I already changed the engine tach cable complete. I also order the inner cable for the rotor rpm since I'd cleaned and lubed it but it still is not acting right. To start with it's the wrong lay cable-suppose to be a right lay and someone put in a left lay at some point-maybe not a big issue initially but over time with friction the wrong lay cable will tend to unwind and cause bounce in the rpm readings I believe.

Another thing about that long rotor inner cable-the book shows the transmission end of it to have a female end and mine was male on both ends. Talking to others indicates there was lots of variation in these cables over the years. I called the cable fabrication shop and they said they hadn't seen any of the female fittings in a very long time. It just so happens the tang in the transmission where the inner cable would have slid over (if it had been female) was a square hollow piece. Therefore a square male end slides inside it-again not what the book shows but apparently the way a lot of them came from the factory or were changed to over time in the field as parts availability changed.
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Re: Transmission rotor rpm cable and dual tach

Postby Ken_Shea » Sun Jan 06, 2013 2:55 pm

$500 bucks now, one can easily forget just how far inflation has taken us till you look back, had mine overhauled about mid 1970 and quite certain the cost was less the $80.
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Joined: Fri Nov 02, 2012 10:13 am

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