magneto problems

[Eric_Phillips]

I have a '65 Gravely L8 with no spark. I tested the cutoff switch and when not pressed it has continuity to ground. I started tracing the short back into the magneto. From the points I disconnected the wire to the cutoff switch, the condenser and the wire to the coil. The terminal on the points has continuity to ground. There is no continuity from the condenser body to its wire lead. There is continuity between the insulated wire off the coil and ground, the coil ground wire was still connected to ground. There is no continuity between either the ground or positive wire of the coil and the spark plug connection on the coil. I did the testing with a digital multimeter. I either got no tone and no reading or it toned and gave a reading of 0 ohms. I am assuming the points should not have continuity to ground since this is the connection that gets shorted by the cutoff switch. I think the condenser is good. What about the coil? This thing has me baffled since 5 years ago it was running. It has sat in the barn since then because of a fuel system problem and I fixed that. The points look clean and in good shape so I can't figure out what could have gone wrong.

 

[rustydollar]

Five years is a long time for tungsten contact points to sit idle, they probably have formed a coating of oxide on the surface, try filing them then recheck the gap.

Anther possibility is that the impulse drive has a stuck spring, are you able to hear the magneto give a sharp clicking sound when turning the engine over slowly.

If the points were closed during your test they would have shown as grounded.

 

[Eric_Phillips]

Yes the impulse drive sounds like it is working.

Are you saying the only time the terminal of the cutoff switch is not grounded is when the points are open?

The points looked clean but I can dress them a little to ensure they are clean.

 

[rustydollar]

Yes the impulse drive sounds like it is working.

Are you saying the only time the terminal of the cutoff switch is not grounded is when the points are open?

The points looked clean but I can dress them a little to ensure they are clean.

Technically you do not require any external wires connected to the mag, the brass screw nut terminal top right hand side when grounded kills the mag by shorting out the condenser.

If dressing the points wont bring life to the magneto, I would first replace the condenser then if the magneto still refuses to make spark with the cap removed use a thin screw driver to probe the magnets to see if the screwdriver is attracted'

It's possible your magneto magnets have lost their magnetism and need to be recharged.

Here's a very well written article that explains the problem and the fix.

The Why and How of Recharging Magneto Magnets - Restoration - Gas Engine Magazine

 

[PILOON]

I would suspect that condenser as the most likely culprit, that is after eliminating obvious things as shorts, rusted points broken wires etc.

 

[rustydollar]

I would suspect that condenser as the most likely culprit, that is after eliminating obvious things as shorts, rusted points broken wires etc.

My money is on lost magnetism.

 

[PILOON]

My money is on lost magnetism.

4 sure a possibility but also the most costly component so eliminating all other causes first is a must IMO.

As an aviation mechanic I worked an my fair share of mags as every engine had 2 mags.
At that we always replaced the points and condenser as a pair but here we are talking a tractor and not an A/C.
FYI many an aircraft used basic tractor mags with parts actually interchangeable but prices 'sky high'. (pun intended)

 

[rustydollar]

4 sure a possibility but also the most costly component so eliminating all other causes first is a must IMO.

As an aviation mechanic I worked an my fair share of mags as every engine had 2 mags.
At that we always replaced the points and condenser as a pair but here we are talking a tractor and not an A/C.
FYI many an aircraft used basic tractor mags with parts actually interchangeable but prices 'sky high'. (pun intended)

The difference between a tractor magneto and the ones used in aircraft it that the later had to be very reliable, they used platinum contact points and some mags had two sets installed for reliability and safety.

Also you;ll find platinum contact sets were used on very old stationary hit and miss engines, the platinum alloy used in the contacts was 80% platinum with 20% iridium. The iridium was used to harden up the platinum making it more durable.

Spark Plug Inspection and Maintenance – Breaker Point Inspection

 

[Eric_Phillips]

Thank you everyone for the information. After doing more research in how an ignition system works I realized I had the functioning backwards. I always thought it was the closing of the points that made the spark fire not the opening of the points. I also learned that just blindly testing the cutoff post for continuity will most likely not tell you anything since the engine is most likely to stop with the points closed. Hopefully I will be able to get out and do some additional testing this week.

The magnetism thing sounds interesting. I am hoping that is not the issue since I didn't find the link very clear on how to re-magnetize the magnet.

 

[Eric_Phillips]

I checked the points and when open the cutoff post has no continuity to ground so they do break. I checked the gap and it seemed a little tight so I recapped them. I then hooked everything back up and tested the cutoff post and sure enough there was continuity to ground again. I disconnected the coil and the wire to the points and the ground wire is shorted, no resistance. From the spark plug terminal to either the ground or points wire is open, no continuity at all. It is a Zico X5700B coil. Am I correct that this is a bad coil?

 

[rustydollar]

I checked the points and when open the cutoff post has no continuity to ground so they do break. I checked the gap and it seemed a little tight so I recapped them. I then hooked everything back up and tested the cutoff post and sure enough there was continuity to ground again. I disconnected the coil and the wire to the points and the ground wire is shorted, no resistance. From the spark plug terminal to either the ground or points wire is open, no continuity at all. It is a Zico X5700B coil. Am I correct that this is a bad coil?

Disconnect the wire connected to the outside terminal, keep the lose end away from the terminal. Crank your machine over now and see if there is spark, or if you go the route to start the engine and she fires up you can stop the engine by grounding that terminal with a screw driver.

Testing your coil maybe a futile effort unless your sure which coil is being tested, inside the main coil there are primary and secondary coils, the latter coil produces the high voltage spark supplied to the spark plug.

Some magnetos came equipped with a kill button, shown below.

 

[rustydollar]

Your coil obviously looks much different than the one shown in the youtube video but the procedure for testing is the same.

 

[PILOON]

Magneto coils will share a common ground.
One side will read low resistance while the output will be very high, the high is the one that goes to the plug.
Points switch the low side.
In that magneto coils are 'potted' I suggest that rarely do they go bad.
The main usual problem will be the capacitor or possibly badly pitted or glazed points.
As a remedy the points can be 'dressed' (fine emery or a file) but that is not really permanent. (dressing damages the fine polished hardened surface)
The usual recommendation is to replace points and condenser as a pair.
Point gap is somewhat critical as over or under changes the timing.

My 2 cents, hope I help a bit.

 

[Eric_Phillips]

Your coil obviously looks much different than the one shown in the youtube video but the procedure for testing is the same.

The first coil he tests looks to be the same coil I have. When I test the primary I get no reading so it looks like the primary is open. When I check the secondary I get 0 ohms like it is shorted. Being $60 for a new coil I just wanted to make sure it was the coil and not something else.

Wouldn't burnt or corroded points show some resistance when closed?

 

[rustydollar]

Wouldn't burnt or corroded points show some resistance when closed?

Not unless you dressed the contacts to remove any surface oxides present.

 

[Eric_Phillips]

I used an analog meter to test the coil and I checked the accuracy of my digital meter. My meter on only measures 0-2000 ohms with an accuracy of 1.5% + 2 Ohms. So trying to read about 1.2 Ohms and 9000 Ohms won't work. So the analog tester I used said 1 Ohm across the primary and 12000 across the secondary. From what I can dig up this coil is supposed to be 1.2 and 9000. I think this coil is good. My screw driver stuck to the magnets so they are not dead. I guess I start with the cheap stuff and try new points and condenser.

 

[rustydollar]

For those tired of troubleshooting points and condensers along with magneto ignition systems there is life after death.

Here are some alternative replacement systems that will modernize yoru ignition system.

Ignition Solutions for Small Engines and Garden Pulling Tractors

 

[Eric_Phillips]

I put it all back together to give it one more try. Sure enough now I have spark. Not sure what the problem was but now I am back to fuel issues.

 

[DJ54]

Here is a link to quit a few Gravely manuals, from service manuals, for engines, mags., carbs., and attachments. Maybe you can find some useful information in them. They are copies of OEM Gravely manuals in PDF form. GravelyManuals.com - OldGravelys.Info: Gravely Manuals & Parts Lists: Walk-Behind Tractors

 

[Eric_Phillips]

DJ, thanks for the links but I already had the manuals from that site. I cleaned up the carb and it is now running again. Thanks for everyones help.