Tach problem

[Richie the C]

Our M20 J tach  bounces all around, between 600 and 2400 rpm. Engine runs normally, I.e. sounds OK and no indication of surging. Anyone else had this problem?
 

[PT20J]

Mechanical or electric tach? If it’s mechanical you might try disconnecting the cable at the tach and pulling the core out and lubricating it with speedometer cable lube.

[Richie the C]

12 minutes ago, PT20J said:

Mechanical or electric tach? If it’s mechanical you might try disconnecting the cable at the tach and pulling the core out and lubricating it with speedometer cable lube.

 

[Richie the C]

Thanks. How can you tell it mechanical?

[Fly Boomer]

1 minute ago, Richie the C said:

 

Your response got lost in the Internet somewhere.

[Fly Boomer]

Just now, Richie the C said:

Thanks. How can you tell it mechanical?

Now I see it -- carry on.

[PT20J]

I believe all the mechanical tachs Mooney used were 3-1/8" diameter and have the recording hour meter built into the tach. I believe all the electric tachs were 2-1/4" diameter and have a separate recording hour meter. You can tell for sure by looking behind the panel and seeing if a speedometer cable comes out the rear of the tach.

[Richie the C]

It is mechanical. Thanks for the response.

 

[N201MKTurbo]

I’ve seen that happen with Mitchell tachs. They are very sensitive to the tach cable pushing on the input bearing. This is caused by a cable that is worn out. The factory SW tach will run just fine with the warn out cable.

I would suggest getting an electronic tach, your problems will go away.

[Richie the C]

Thank you. Good idea. Mr. Maxwell made the same suggestion.

 

 

[haymak3r]

I have a tach for sale too. from a 79 J  Not sure how compatible they are. It is definitely mechanical.