Aetna Tach’s

[Prudence]

Hello
I have a set of old Aetna 8905 tachs that I’m guessing are 20-30 years old, they are old enough to have been made in Van Nuys, Ca. They look great and test operate fine. I’m installing them on a pair of ford Lehman 120’s. My question is if anyone out there has a manual or knowledge of setting the switches? They only have 3 switches total. I have a set of 8902 sending units installed. Any help would be appreciated.
Brad

 

[tiltrider1]

Contact Aetna, they still exist and were helpful when I approached them 5 years ago.

 

[Prudence]

Old tachs

I contacted Aetna and the support tech didn’t know anything about them. Said he would look into it. Never did hear back.

 

[Mischief Managed]

if there are only 3 switches with two positions each, there are only 8 possible configurations. You could try each one and see which makes the most sense relative to a known idle RPM.



000

001

010

011

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111



If your tach drive is off the camshaft, it will be at half engine speed so you would expect to see 3 pulses per engine revolution. Try 010 (off on off) and see if it works.


IF the tach drive is off the crankshaft, you would expect 6 pulse

 

[ancora]

As an aside for you Aetna digital tach owners: I had a tach that stopped reading. Called Aetna and the tech told me to set all the dip switches to zero and then reset. Worked like a charm.

 

[Mischief Managed]

if there are only 3 switches with two positions each, there are only 8 possible configurations. You could try each one and see which makes the most sense relative to a known idle RPM.



000

001

010

011

100

101

110

111



If your tach drive is off the camshaft, it will be at half engine speed so you would expect to see 3 pulses per engine revolution. Try 010 (off on off) and see if it works.


IF the tach drive is off the crankshaft, you would expect 6 pulse

In retrospect, I am probably wrong about the number of pulses per revolution for the sender you are using, I cannot recall how many pulses the sender produces per sender revolution, it may be just two or even just one... But anyway, with only 8 choices, it should not take long to figure out the correct switch setting.

 

[C lectric]

I contacted Aetna and the support tech didn’t know anything about them. Said he would look into it. Never did hear back.

Don't give up so easily. Call them again and get a more experienced person.

Examine the guages closely for any part numbers, serial numbers, and model numbers. Any marking at all. Maybe even a photo to send when you get an email address.

Have those numbers/names at hand.

 

[Prudence]

Thanks for all the help. I’m going to follow Mischief Managed instruction this weekend - can’t hurt. I’ll post the outcome.
All the info I have says 8 ppr for the lehmans
Aetna Engineering tech support is shared with Fireboy and Xintex so finding a old Tachometer person might be a challenge.

 

[ancora]

According to my Aetna engine PPR selection guide, the Ford Lehman dip switch set-up looks like this:



SW2 SW1

1 2 3 4 1 2 3 4 5 6 7 8

0 0 0 0 0 0 0 0 1 0 0 0