<VV> tach

[Frank DuVal]

My 64 Spyder coupe sticks at 3000 rpm. I think it is a gage fault, not 
electrical. Like a piece of dirt preventing the needle from passing the 
3000 mark. I have not had time to dissassemble it to check. But, I have 
had other meters in electronics stick due to dirt.

Frank DuVal

Bryan Blackwell wrote:

>I've seen a couple posts on the inner workings of the tach - I'm not  
>enough of an electrical guy to recall any of it, but you might dig  
>through the archives a bit.  Here's one post regarding calibration  
>that may help from Frank "man of many nicknames" Burkhard:
>
>Les, Jim and VVers,
>     Jim jostled my memory on this tach calibration question.  The 6  
>cyl.
>Corvair engine produces 3 ignition coil pulses per revolution since  
>all 6
>cylinders fire every 2 revolutions of the engine.  If the engine is  
>running
>at 2400 rpm (or 40 revs per second) that makes 120 pulses per second  
>sent
>to
>the tachometer.  This is exactly the same number of 12 volts pulses (or
>peaks) of DC voltage produced by a full wave rectifier battery charger.
>The
>battery charger takes 120 volts AC at 60 cycles per second and  
>converts it
>into 12 (more like 15) volts DC with 120 pulses per second IF the  
>charger
>uses a full wave rectifier.  If it uses a half wave rectifier, it  
>produces
>60
>pulses per second DC which would be equivalent to the Corvair engine at
>1200
>rpm.
>The power company takes considerable pains to maintain the 60 cps quite
>accurately since it governs the speed of electric clocks and other  
>devices
>that depend on the frequency to control motor speed of things like  
>VCRs and
>CD players, etc.
>     See, Les, no begging required !!(:-)
>     Frank "gauge lover" Burkhard
>
>On Sep 25, 2008, at 4:09 PM, Arend Huisman wrote:
>
>  
>
>>i have installed a Spyder dash in my '64 monza; everything works  
>>well except for the tach, which gives a reasonable good idle speed,  
>>but doesn't go further up than 1500 rpm. I looks like it responds  
>>to the vacuum directly. It is connected to the minus pole of the  
>>distributor coil as discribed in the electrical scedule (Classic  
>>Corvair, Bob Helt) Can someone help me out?
>>    
>>
>
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