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RPM Unit

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shinden33

Joined: 02 Nov 2007
Posts: 39

Posted: Tue Apr 28, 2009 9:21 am Post subject: RPM Unit

All,



Lost my RPM indication on my '52 last weekend.  Pulled the cannon plug on the back of the RPM sender apart and did not find any bad connections.  Continuity checked the wires to the back of the gauge and they all checked as well.



Question 1.  There are three pins coming out of the sender and four going into the back of the instrument.  Where does the fourth one go?



Question 2.  Anyone have and RPM sender and how hard is it to replace?



N8252 

Scott

dougsappllc(at)gmail.com
Guest

Posted: Tue Apr 28, 2009 9:36 am Post subject: RPM Unit

Did you loose indication in BOTH pits?

  

 Doug

 On Tue, Apr 28, 2009 at 10:21 AM, shinden33 <scott.t.glaser(at)gmail.com (scott.t.glaser(at)gmail.com)> wrote:

  	  Quote: 	
		  --> Yak-List message posted by: "shinden33" <scott.t.glaser(at)gmail.com (scott.t.glaser(at)gmail.com)>

 

All,



Lost my RPM indication on my '52 last weekend.  Pulled the cannon plug on the back of the RPM sender apart and did not find any bad connections.  Continuity checked the wires to the back of the gauge and they all checked as well.

 

Question 1.  There are three pins coming out of the sender and four going into the back of the instrument.  Where does the fourth one go?



Question 2.  Anyone have and RPM sender and how hard is it to replace?

 

N8252

Scott





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shinden33

Joined: 02 Nov 2007
Posts: 39

Posted: Tue Apr 28, 2009 9:52 am Post subject: Re: RPM Unit

Yes. I verified that it was not a single instrument failure.

mark.bitterlich(at)navy.m
Guest

Posted: Tue Apr 28, 2009 10:14 am Post subject: RPM Unit

The Tach Gen is very easy to replace.  Assuming the M-14.  Not sure of

the Housai, but it probably is close to the same.  The Tach Gen on the

M-14 has a big bright silver colored ring with little finger type

indentations that allows it to be spun right off.  You un-spin (new

word!) the ring, and pull straight out on the tach gen and out it comes.

Take the tach gen shaft and clamp it into an electric drill.  Spin the

crap out of it and measure the AC voltage coming out.  Should be the

same voltage on each pin at the same RPM.  If not, it is bad.  



Mark Bitterlich

 



--

gill.g(at)gpimail.com
Guest

Posted: Tue Apr 28, 2009 10:19 am Post subject: RPM Unit

I had a similar problem with my CJ.  Continuity checked ok but problem

persisted.  I resoldered the connections in the cannon plug and made sure

female ends were tight, problem went away.



Gill



--

mark.bitterlich(at)navy.m
Guest

Posted: Tue Apr 28, 2009 10:35 am Post subject: RPM Unit

Gill is absolutely correct.  



More on that:  



The solder used in those cannon plugs is extremely poor quality and it

develops cold fractures very easily.  It is the FIRST PLACE TO GO when RPM

indications go bad.  The wire itself is also very questionable.  I

resoldered mine.. More than once.  Then I said screw it and soldered in high

quality Teflon insulated aircraft quality wire to the plug, went back about

a foot and used environmental splices to splice back into the Russian wire.

Problem gone forever.  Then the Tach Gen itself went bad.  Came up with the

drill method to verify it.  This also works with the cannon plug hooked up

and driving the actual instruments in the cockpits.  



Mark Bitterlich



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shinden33

Joined: 02 Nov 2007
Posts: 39

Posted: Tue Apr 28, 2009 11:32 am Post subject: Re: RPM Unit

What is voltage output range roughly?

mark.bitterlich(at)navy.m
Guest

Posted: Tue Apr 28, 2009 12:22 pm Post subject: RPM Unit

I really do not remember. 



More than a few, less than a lot. 



I'll try to remember to go spin one and see.  However, very simply the

faster you turn it, the more it will put out, and not by millivolts, but by

10's of volts.  



Mark

 



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shinden33

Joined: 02 Nov 2007
Posts: 39

Posted: Tue Apr 28, 2009 4:06 pm Post subject: Re: RPM Unit

Good enough.  I'll give it a shot and see how it goes.  Thanks for the gouge all!



S

mike_beresford(at)yahoo.c
Guest

Posted: Tue Apr 28, 2009 9:55 pm Post subject: RPM Unit

Hi all



I recently had trouble with my RPM indicators. Also checked wiring continuity, all seemed fine. Turned out that the problem was in the generator itself, it had "lost" a phase. Initial test done by checking the voltage in turn between each pin and the earth. Replaced the generator, problem went away. Thanks to Mark B for his sound advice on that one.



A few points, which some of the experts may wish to confirm:

- As far as I can make out,the fourth pin on the connector in the cockpit is not used.

- Check your wiring layout before disconnecting anything. When I first checked my wiring, I found pin 2 in the engine bay was connected to pin 3 in the cockpit, and pin 3 in the engine bay to pin 2 in the cockpit. I assumed that this was an error, so I connected pin 1 to 1,pin 2 to 2, pin 3 to 3. RPM indicator then proceeded to work backwards! Swapped wires 2 and 3 around, indicators work properly again. 

- I have been advised by a few people to ensure that the wires are properly screened.



You may also want to check the connector plug in the engine bay. Some time back I had erratic indications, sometimes it worked, sometimes it didn't. I found that the insert (bakelite) was loose within the cannon plug, and the pins themselves were loose within the insert. Ss I tightened the plug onto the tacho generator it simply pushed the pins backwards resulting in a very poor contact. Bit of epoxy sorted the problem out.



Blue skies

Mike

--- On Tue, 28/4/09, Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E <mark.bitterlich(at)navy.mil> wrote:



[quote] From: Bitterlich, Mark G CIV Det Cherry Point, MALS-14 64E <mark.bitterlich(at)navy.mil>

 Subject: RE: Re: RPM Unit

 To: yak-list(at)matronics.com

 Date: Tuesday, 28 April, 2009, 11:21 PM

 I really do not remember. 

 

 More than a few, less than a lot. 

 

 I'll try to remember to go spin one and see.  However,

 very simply the

 faster you turn it, the more it will put out, and not by

 millivolts, but by

 10's of volts.  

 

 Mark

  

 

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