mikewest

change the gearing on a antique mechanical tachometer?

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I have a teens  Corbin Brown tachometer I have connected to my engine off the end of the camshaft. I know the camshaft runs at  50% of crankshaft speed. Has anyone reading this had any experience changing the gearing in the camshaft or know of someone that can? Thank you Mike

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Not sure you would change the camshaft gearing, it would never stay in time with the crank.  Yes it absolutely runs 1/2 crank speed.  Assuming your tachometer was designed to measure crank speed revs you could just double the tach reading.  If that doesn't work for you and you have a convenient way to connect the end of the cam to a cable or input shaft of a small gear box you could try to find or make a 1 to 2 ratio up-drive to go between the tach and the cam.  To get some expert advice and maybe an up drive or conversion of your tach you could try Bob's Speedometer  

 

https://www.bobsspeedometer.com/1/120/index.asp

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Dave, You are correct. My tachometer came off a period starter /generator test bench and it is 1 to 1 gearing. Im not going to monkey with the gearing on the motor. I think the 2-1 gearbox will be the easy fix. Ill check with Bobs. Thanks Mike

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Mike... I looked into fitting a tach to my Mitchell and found that they actually aren't geared to the shaft. They use something akin to an old engine governor...spinning weights pressing against a spring. The reading on the dial is determined by the strength of the spring. I've never taken one apart to look inside because I eventually decided not to do it but I still have the tach...it's yours if you can use it.

 

j

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Joe , I have several tachs and have the one I want to use. I wonder if they could be adjusted to read more correct. I haven't found much info on them. The so called  expert I called said get some stickers and change the numbers to half of what the say.... OK I can do that without a sticker.

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