MTH Flywheel Tach

JPThutOGR Forum Member

Gentlemen, I am in need of some information about MTH motor flywheels and how they affect speed control. I needed to replace a bad motor on a Railking RS3 and was able to find the correct size motor for sale used. When I mounted the motor I realized that the flywheel on the "new" motor was just slightly larger than the one I had removed. The sensor, when mounted in its holder touches the flywheel so I mounted it with double-stick tape on the outside of the holder. That makes it about 1/8" away from the flywheel. The engine runs but the speed steps are quite a bit too fast. Does the sensor need to be closer to the flywheel or does the slightly larger size of the wheel cause it to run too fast? Thanks for your help.

JP Thut

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10/15/224:38 PM

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DanrOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

That sensor should be about 1mm away from the tach strip. That would be about 1/32” or 0.039 if you have a feeler gauge.

10/15/227:48 PM

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JPThutOGR Forum Member

Thanks Dan.

John

10/15/227:53 PM

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gunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

That picture shows the tach reader WAY too far from the flywheel, just FYI.

10/15/228:02 PM

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JPThutOGR Forum Member

Thanks, that's why I included it.

10/15/2211:38 PM

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Alan MancusOGR Forum Member DIGITAL SUBSCRIBER

some techs just use the thickness of a Dime which is close enough but also feeler gauges are not expensive from harbor freight! also, you can change the tach reader they make which extends the height so it will be closure to the flywheel!

Alan

10/16/229:04 AM

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Engineer-JoeOGR Forum Member SUPPORTING MEMBER

shouldn't the tach board be slid inside the holder mount?

10/16/221:16 PM

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JPThutOGR Forum Member

Yes, but as I stated, it hits the flywheel when it is placed there. Not sure why.

10/16/221:38 PM

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gunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

@JPThut posted:
Yes, but as I stated, it hits the flywheel when it is placed there. Not sure why.

Well, I can tell you why. The tach sensor you're using has the spacer under the sensor, for that motor/flywheel combination, you need the remove the spacer and have the sensor flush with the PCB in order to have the proper clearance.

10/16/221:47 PM

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harmonyardsOGR Forum Member

@gunrunnerjohn posted:
Well, I can tell you why. The tach sensor you're using has the spacer under the sensor, for that motor/flywheel combination, you need the remove the spacer and have the sensor flush with the PCB in order to have the proper clearance.

It sure does have the wrong sensor for that bracket John,…..he needs the sensor without the spacer to work with that tach bracket,…….

Pat

10/16/222:12 PM

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JPThutOGR Forum Member

Is the spacer difficult to remove? I have a friend who has a wheel/flywheel puller and I also could switch the flywheel from the old bad motor to the new motor so the sensor would be spaced correctly.

10/16/225:39 PM

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harmonyardsOGR Forum Member

Swapping the sensor would be a safer, easier move, I’d think,…..you always can risk damaging those gears & flywheels trying to remove them,…..

Pat

10/16/225:57 PM

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gunrunnerjohnOGR Forum Member SUPPORTING MEMBERDIGITAL SUBSCRIBER

You're making this way too difficult! Pulling flywheels is the hard way. If you don't know what you're doing pressing the flywheel back on, you can wreck the new motor, I've watched someone do it. MTH has the tach reader sensors with no spacer on their parts site.