Kohler 161 7HP Dead

[Junior Marbles 17]

I troubleshot the dead 161 single-cylinder engine in my Troybilt Horse (7HP) this far: 

Fuel delivery: check

points + condenser : check

Spark Plug: check

 

The wire coming from under the magneto cover to the points shows a short. 

Before I take the cowling off and get deep into the magneto section: any ideas why there is a short?

Is there a typical cause for shorts in these engines' electrical supply? (If I had a schematic, I could trace it a bit easier, but have not yet found one online.)

Thanks a bunch!

JM

 

P.S.: Until this happened, the engine would always start on the first or second pull.

 

 

Edited October 9, 2022 by Junior Marbles

[953 nut 56,179]

10 minutes ago, Junior Marbles said:

 

The wire coming from under the magneto cover to the points shows a short.

Did you have the ignition points and condenser disconnected from that wire while testing it?

To check the magneto you will need a very good quality ohm meter. Here is a rundown on the procedure.

 

The question of testing a Magneto has come up on Red Square from time to time and the simplest explanation I have found was on a site devoted to those Green tractors (sorry about that) I have a NOS magneto coil and a couple of used ones on the shelf and my results are the same.

 

The resistance of the secondary should be around 8k to 10k ohms. The resistance of the primary should be around 1.0 ohm. You need a good digital meter to tell the difference between a shorted primary and a good primary. If it really is shorted (unlikely) check the wiring harness where it enters the stator plate and under the clamp for a pinched or bare wire.

 

Both the primary and secondary coils surround an iron core and are grounded through the core to the stator plate. While the points are closed the rotating flywheel magnets induce a voltage and current flow through the primary coil which is made up of a few hundred turns of heavy wire. This current flow creates a magnetic field. When the points open the current flow stops and the field collapses through the secondary coil which is made up of thousands of turns of fine wire. This collapsing magnetic field creates a very high voltage in the secondary due to transformer action and the high voltage arcs across the electrodes in the spark plug.

The resistance of the primary is measured between ground (engine, or stator plate if the stator is dismounted) and the wire from the points and condenser. Resistance of the secondary is measured between ground and the spark plug connector at the end of the plug wire

[rmaynard 15,734]

My K161 would not produce a spark. After two owners being unable to locate the problem, I took the flywheel off and found that the insulation on the primary wire to the coil was worn and shorting to ground.

 

[Junior Marbles 17]

Did you have the ignition points and condenser disconnected from that wire while testing it?

 

Yes.

 

To check the magneto you will need a very good quality ohm meter.

I will measure again, this time with my $300 Fluke, which is very accurate in the < 1Ω range.

Thank you, I will update this thread as soon as I have the measurements.

 

JM

[Junior Marbles 17]

Resistance between ground and wire coming from the magneto: 0.7Ω

Resistance between ground and (+) of spark plug wire: infinite  i.e. open.

 

Eager to take your advice what to do next.....

[953 nut 56,179]

10 hours ago, Junior Marbles said:

Resistance between ground and wire coming from the magneto: 0.7Ω    Should be good

Resistance between ground and (+) of spark plug wire: infinite  i.e. open.   I would remove the spark plug wire from the coil and check resistance directly from the Magneto coil. Could be an open in the plug wire, if not then remove the coil, clean everything and try again, could be corrosion preventing continuity.  Always do the free stuff before buying a new part you may not need.

 

Eager to take your advice what to do next.....

 

[Junior Marbles 17]

Next problem: I cannot get the flywheel off, and have already nicked one of the cooling fins, trying to wedge a bar to keep the wheel from turning as I try to apply torque (see photo).

First question: has the central nut (15/16) a regular thread, i.e. counter-clockwise = loosening?

Second question: how to get the nut off?

Edited October 13, 2022 by Junior Marbles

[Heatingman 971]

7 minutes ago, Junior Marbles said:

Next problem: I cannot get the flywheel off, and have l ready nicked one of the cooling fins, trying top wedge a bar to keep the wheel from turnign as I try to apply torque (see photo).

First question: has the central nut (15/16) a regular thread, i.e. counter-clockwise = loosening?

Second question: how to get the nut off?

Have an impact wrench?

Edited October 13, 2022 by Heatingman

[Junior Marbles 17]

Yes. But I need to somehow lock the flywheel but canot find a suitable attachment point.

[Heatingman 971]

The thread direction is standard. Counter clockwise to loosen.

 

Whats on the other side of the motor? Perhaps you can grab the crank on that end. 
 

Or maybe a ratchet strap around the flywheel and around the frame below.

 

 

[Heatingman 971]

The k series manual gives pretty decent base schematics for the motor and various starter arrangements.

 

 

Kohler_k_series_manual.pdf

[Junior Marbles 17]

Great resource, that manual. Thank you!

I will try to lock the engine by engaging a gear, then using an impact wrench.

[953 nut 56,179]

Your flywheel probably has one or more holes drilled into it for balancing, find a piece of round stock (I think it was 5/8") insert the round stock in the hole and brace the other end against the frame on the left side, now you can apply lots of torque to the nut and the flywheel will stay put.

[Junior Marbles 17]

Great advice. I already thought of it, but was afraid to bend the tiller's bumper/frame. Will try the stock in the deepest hole.

[Junior Marbles 17]

Update:

Nut is off (thanks to a neighbor's impact tool) and flywheel is off, too. I then measured again the secondary resistance at the spark plug, and it now read correctly (around 5.5kΩ). God knows what condition made it read open before.

But still no spark. I installed yet another brand-new condenser, no luck. After correctly gapping, I also measured the points when closed, and they ready 0Ω, i.e. no corrosion in the way of conductance. Also installed a new spark plug.

 

In any event, it's time to buy a new magneto coil, they are cheap enough to eliminate the original part having some freaky condition beyond two healthy-measuring coils. (Is there a condition of no spark, even when both coils of the magneto read correctly?) These coils are suspiciously cheap. I hope the Chinese-made ones don't add a new problem...

 

 

[Junior Marbles 17]

On 10/16/2022 at 7:35 PM, Junior Marbles said:

...Is there a condition of no spark, even when both coils of the magneto read correctly?....

 

 

That is the big question for me right now, otherwise I am tapping in the dark where to turn my attention to.

[wallfish 17,114]

On 10/16/2022 at 10:35 PM, Junior Marbles said:

(Is there a condition of no spark, even when both coils of the magneto read correctly?)

Bad magnets on the flywheel

Coil wired backwards

[953 nut 56,179]

On 10/16/2022 at 10:35 PM, Junior Marbles said:

Is there a condition of no spark, even when both coils of the magneto read correctly?

Air gap between the magneto and flywheel not correct.

[Junior Marbles 17]

5 hours ago, wallfish said:

Bad magnets on the flywheel

Coil wired backwards

That would not explain the occasional spark I got from the spark plug early on in my investigations.

[Junior Marbles 17]

4 hours ago, 953 nut said:

Air gap between the magneto and flywheel not correct.

The machine worked flawlessly last year- no air gap changes I could even theoretically think of. Air gap is also not adjustable on that engine, as far as I can determine. I also found the magneto assembly nicely torqued to the back plate.

[rick 237]

I have a TB Horse with a K161 Kohler left for repair here, owner said "someone told me it needed a carb kit".  I did clean and rebuild the carburetor, the engine started and ran for a while and died.  No spark.  Replaced ignition parts one by with new or switched parts from my running K161 from my TB Horse all but the flywheel.  No luck.  This winter I'll try again double checking every thing carefully.  He bought another tiller so left it here. 

[Heatingman 971]

Scrub the inside of the flywheel. Clean the mounting points of the magento to a shine. 

 

Make sure all battery terminals and wire connection are clean. Same for ground connections.

 

no ground, no function. Make sure the case of the magneto to battery negative has .1 ohms resistance - good continuity. 

 

Just had a voltage regulator/rectifier not working. Battery was not recharging. Had no continuity between the case of the rectifier to battery negative. 
 

ran a dedicated wire to a good ground. Problem solved. 

Edited October 19, 2022 by Heatingman

[Junior Marbles 17]

8 hours ago, Heatingman said:

Quote

Scrub the inside of the flywheel. Clean the mounting points of the magento to a shine.

Did that already

 

Quote

Make sure all battery terminals and wire connection are clean. Same for ground connections.

No battery on a 7HP Horse. It's the old pull rope.

 

Quote

no ground, no function. Make sure the case of the magneto to battery negative has .1 ohms resistance - good continuity.

Mine has .03Ω.

 

Quote

Just had a voltage regulator/rectifier not working. Battery was not recharging. Had no continuity between the case of the rectifier to battery negative. 

ran a dedicated wire to a good ground. Problem solved.

Does not apply to my model. No battery.

 

 

Tomorrow I will install the new Magneto. We will see...

Edited October 20, 2022 by Junior Marbles

[rmaynard 15,734]

Clean the contacts on your points and set them to.020. I don't know how many times I've forgotten that points oxidize just sitting there. 400 grit sandpaper does a great job. Even new points can be oxidized.

[Junior Marbles 17]

Done that, too. Measured resisstance when closes: 0.0Ω. No spark still...