Adding a Tach Gauge?

[Craftsman Garage]

Im looking to add a tachometer gauge to my 2014 Craftsman T7400 with a Kohler KT735 engine. The tractor already has 2 holes for 2.25" gauges so I would be replacing the ammeter with a tach. How would I set it up to get the engine's rpm signal though? Has anyone done anything similar before? Thanks for the help.

 

[StarTech]

Most tachs for small engines are inductive pickup.Those just have a lead the wraps around one the spark wires.

But what tach gauge are looking at installing?

 

[Craftsman Garage]

Just a generic tach. It has to be 2 1/4" to fit in the factory hole, but those are fairly easy to find. My only question is how would I get the signal? I have one of those tachs with a wire that you loop around and that's what I'm trying to get away from. These tachs say to attach the signal wire to the coil ground of cars, so would it be the same for this engine with magnetos? I might be overthinking this. I'm looking at this amazon one: https://a.co/d/0fxlbwyk

 

[Auto Doc's]

I have to ask.... Why do you want a tach?

Those engines are designed to run at idle or full throttle at 3400-3600 RPM.

 

[Craftsman Garage]

I have to ask.... Why do you want a tach?

Those engines are designed to run at idle or full throttle at 3400-3600 RPM.

Convenience, checking rpm under load (I'm suspecting the rings may be worn already, it feels weak compared to a newer engine of the same model that roars to life), idle adjustments, etc. I think it would be more useful than the ammeter that is there right now.

 

[Auto Doc's]

Have you considered checking the valve lash adjustment? Early adjustment just after break-in is imperative.

 

[Craftsman Garage]

Have you considered checking the valve lash adjustment? Early adjustment just after break-in is imperative.

I think I do need to adjust the valves. It has 170 or so hours and I bought it from an old guy at 150 hours.

 

[StarTech]

Just a generic tach. It has to be 2 1/4" to fit in the factory hole, but those are fairly easy to find. My only question is how would I get the signal? I have one of those tachs with a wire that you loop around and that's what I'm trying to get away from. These tachs say to attach the signal wire to the coil ground of cars, so would it be the same for this engine with magnetos? I might be overthinking this. I'm looking at this amazon one: https://a.co/d/0fxlbwykView attachment 72667

Diesel RPM Tachometer 2-1/16" 52mm Automotive Tacho Gauge for Car Interior 0-6000RPM 2" RPM Meter for 2-8 Cylinder Diesel Engine 12V​

Are you dealing with some stupid AI?

I see at least a couple problems.

The first one is a major one. Diesel engines don't have ignition coils or even spark plugs; unless, it is some version that I never about ever.

Even a gasoline engine ignition system are a different beast than magneto systems. On small engines you have no access to the coil's ground. It is the frame of the coil and is already bolted to ground.

These vehicle tachs simply will not work on magneto systems. You have to pick-up the ignition impulses off the plug wires. Now someone could come up with a trigger circuit that pickups an impulse off the flywheel but that would take some doing.

 

[Craftsman Garage]

Are you dealing with some stupid AI?

I see at least a couple problems.

The first one is a major one. Diesel engines don't have ignition coils or even spark plugs; unless, it is some version that I never about ever.

Even a gasoline engine ignition system are a different beast than magneto systems. On small engines you have no access to the coil's ground. It is the frame of the coil and is already bolted to ground.

These vehicle tachs simply will not work on magneto systems. You have to pick-up the ignition impulses off the plug wires. Now someone could come up with a trigger circuit that pickups an impulse off the flywheel but that would take some doing.

I don't think so. The diesel and gas gauges are the same as far as I know because both just use a signal wire. On a diesel it would go to a sensor, and a Gas would go to the coil ground. I could always be wrong though.

 

[StarTech]

Okay explain this wiring diagram that appear to source the generator/Alternator for the impulses. Note this the wiring diagram for the gauge you linked. And your image provided don't even the diagram. So what gauge is it? This particular gauge will require a tach to adjust it.

So I need to compare apples to apples and not apples to lemons. OR that how I research things here.