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Detroit tach adapter

Posted By Jeeperscreepers Last Month
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Jeff Lakaszcyck
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Tony Bullard (4/3/2021)
Here's a possibility for Jeff and Dan's buddy. The buddy may be looking for the 2:1 adapter because the techometer he has is 1:2 for a four cycle engine. If his tach was 1:1 as Jeff's is he wouldn't need the adapter. Jeff needs a 1:2 adapter or a 1:2 tach because he has a two cycle tach. If they swap tachs all problems may be solved.


I think my tach is 3-1/4 inches in diameter. 



Jeff
Jeff Lakaszcyck
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tundra (4/3/2021)
how are ya gettin along jeff ?????


Pretty good Jim, a little better every day. I'm about 90-95 percent, still can't pick up anything real heavy but I'm gaining on it ! 




Jeff
Tony Bullard
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Here's a possibility for Jeff and Dan's buddy. The buddy may be looking for the 2:1 adapter because the techometer he has is 1:2 for a four cycle engine. If his tach was 1:1 as Jeff's is he wouldn't need the adapter. Jeff needs a 1:2 adapter or a 1:2 tach because he has a two cycle tach. If they swap tachs all problems may be solved.


Tony
tundra
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how are ya gettin along jeff ?????
Jeff Lakaszcyck
Posted 2 Weeks Ago
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Thanks Tony, that is what I had been thinking but I'm glad you confirmed it. 

Jeff
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I haven't been able to get in touch with the fellow.  Doesn't answer the phone and no voice mail.  May reach him tomorrow.

Dan Cornett
Tony Bullard
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Jeff Lakaszcyck (4/1/2021)
Dan, I have been meaning to ask you if you had any of these, the tach I installed in my Federal is reading 1/2 speed. My thread size is 7/8-18. Straight or 90 degree would work. Here is a photo of the drive. 

http://forums.justoldtrucks.com/uploads/images/d68a867a-b603-442d-9125-5739.jpg


Jeff if that is off the distributor drive it is at half engine speed. The tach should be 2:1. It should read twice cable speed. Or as Dan said you need a 1:2 ratio adapter.


Tony
Tony Bullard
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Junkmandan (4/1/2021)
I have several coffee cans full of them .  You may know there's 3 different key sizes , plus at least 2 square drive sizes .............and probably Detroit used 'em all .  What Tony shows looks like .104 square drive .
By reverse rotation, I assume you mean that if input is clockwise, output should be CCW.   

Dan C.------I certainly don't need all mine .     But which one ?

After rereading Dan's description I think I see what he is looking for.
"a 90 degree, 2 to1, reverse tach adapter for a 71 series"
2:1 input to output. CCW input CW output to direct drive a 2:1 CCW tach.
This adapter would be for the right shaft.

I think all the drives are tang drive.


Tony
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Adding to the complexity , an option on V 71 and 92 engines was off the blower shaft...............which i prefer, because it can't interfere with accessories that might be added or changed later. as an engine might get repurposed .
Keep in mind also, rotation is changed on 53s as opposed to 71--92s.
As you say............MOST tacks read half crank speed, but Detroit sold lots of industrial and marine engines thay had a direct mounting provision righ on the rearhousing, with a short 6" cable direct in the tach head with no ratio adapters or cables.
Tony Bullard
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As far as I know most tachs read twice the cable speed and have a CCW left hand input looking at the drive. Most four cycle engines drive the tach at .5 engine speed in a CW right hand direction so they can direct cable drive the tach. All, (most?) Detroits drive the tach at engine speed. Rotation will depend on which shaft, cam or balance, or accessory and which end the the drive is on.
It also depends on the engine arraignment. The same applies to the inline engines.