Tachometer Hook-Up

[olcah]

I was given the tach in the photo. The back sticker says Aquameter A635 636. These tachs are pretty common and I wondered if it can be used with a 1956 RD? I know that the tach must count pulses and as these motors have two coils it might require that it use pulses from just one of the coils. If so the tach would read only 1/2 actual RPM but that would be OK.

Has anyone used this type of tach with mid 1950s OMC non-generator motors? If so, how was it hooked up?
Thank you.

[frankr]

Pretty sure it is useless without the proper amplifier to adapt it to the motor. With the amplifier, it gets its signal from one set of points (center post of the vacuum cut-out switch)

[wbeaton]

Like Frank says, that one is missing the sender and won’t work without it. Model 653 will work on a motor with a magneto. I don’t know with which motors the model 635 works.Some compatible tachs have a built in sender. In either case, two wires go to the motor, one to ground and one to the magneto. The lead to the vacuum cut off switch will work for the magneto lead. The ground can be anywhere on the motor..

Wayne
Upper Canada Chapter

uccaomci.com

[olcah]

Frank and Wayne Thanks for the responses. I thought there might be a problem.

I am thinking about measuring RPM to look at propeller options. Other alternatives are a Tiny Tac or a cheaper knock off. There was a thread awhile back but as I recall no one said clearly if the Tiny Tac worked well on coil/points ignition or if the knock offs worked ok. I think there was trouble getting a clean signal.

Does anyone have any experience with the Tiny Tac or the cheaper knock offs on 1950s motors with coil/points ignitions?

• This reply was modified 6 years ago by olcah.

[garry-in-michigan]

The Tiny Tack works with an inductive pick up – A wire wrapped around a spark plug wire. It works on anything with an ignition. Four cycle motors only show half speed.

• This reply was modified 6 years ago by garry-in-michigan.

[frankr]

Don’t have one and they didn’t exist back in “The Day”, but if I were in business today I’d be looking at one of the new laser tachs for doing such tasks as propping, etc. Apparently you just aim it at the flywheel. Anybody here used one?

[David Bartlett]

Charlie,

I have a “Tiny-Tach” knock-off that I am using. So far so good. It took me a bit to get the setting set to the OMC twins but works good once I figured it out. My Chinese reading skills are lacking.

I have used it on my RD and SD motors, and I am happy with it. I can bring it to Doug’s meet and show you how it works, and let you try it if you want.

David Bartlett
Pine Tree Boating Club Chapter

"I don't fully understand everything I know!"

[olcah]

Dave,
I may not get to Doug’s meet but your experience is just what I need to know. Can you tell me the brand name on your tach?
Thank you,
Charlie

Thanks also to Frank, Wayne and Garry for their responses and info.

[dsaulsbury]

I have used a Tiny Tach on all of my old OMC racers for years with success. I presently use one on my Johnson Stinger 3 cylinder. I found that on alternate firing motors to put the pickup wire on the bottom cylinder and route the wire down into the bottom of the pan to keep it away from any chances of picking up any stray pulses. I have been told they don’t work well on Mercury products that use distributors as the ignition is very “noisy” and confuses the pulse pickups. I never checked to see how accurate they were. I expected they were at least consistent so that would be fine for checking out props. The battery in mine worked for years beyond the the stated life.

[David Bartlett]

Charlie,

I am at work right now so will check tonight and see what make it was.

David

David Bartlett
Pine Tree Boating Club Chapter

"I don't fully understand everything I know!"

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