Oliver 70 Bosch MJC Magneto

[Sturdily7974]

I am working on the magneto for my Oliver 70. I worked on the tractor about 15 or so years ago, purchasing new parts, etc. Well it sat without being finished until now. So far I have not had it running. Currently I am making sure the magneto is timed and putting out good sparks.

When attaching the magneto to the tractor, the drive coupling is not perfectly horizontal. The manual says to match the red tooth on the small magneto gear to the white line on the larger gear. The small gear has a raised tooth but just one tooth before that there is a red paint dot. Well I cannot attach the mag to the drive coupling with the red tooth pointing up, only the raised tooth. I'm not sure why the manual mentions a red tooth when the drive coupling would have to be less horizontal than it is now for that tooth to be accurate.

The mag fires on number 1 just a bit after the white Ignition / Gas timing mark passes by. I'd say the timing is dead on because the piston isn't fully up yet when the timing mark is visible, so just after should be good. So the raised tooth has to be the correct alignment.

I seem to be getting a spark on the number 1 plug when the mag gear hits number 1 and again on number 2. Number 4 never sparks. I've had the spark plugs out and resting on top of the holes so I can see them sparking when I use the starter. 1 and 5 are consistent but the others don't seem to be firing very often.

When hand cranking the magneto, I cannot see a spark sometimes on any of them. I do hear the audible click from the magneto on every fire. But when I crank with the starter and then afterwards go back to hand cranking, the audible click is missing for some time and then after several rotations it's back again.

I'm not sure what all this means but I am going to make a small spark plug wire and purchase a spark tester so I can test close to the mag. Maybe this will tell me if they are all firing or not. The points are gaped and cleaned. I've done what I can except for taking the whole magneto apart and cleaning it up. Not that I want to do that if I don't have to but I cannot find parts for the MJC models online and I don't know of anyone around here that works on them. Sending it out would be expensive too with shipping both ways.

I thought about converting it over to a distributor but since I cannot find the distributor housing assembly that would mount to the tractor, that is also never going to happen. https://www.tractorpartsasap.com/distributor-remanufactured-delco-remy-1111412-205103.html This would never work without it.

I have read that these magnetos are just weak overall. Perhaps it is sparking as good as it ever will and I just cannot see it every time. Should I move on to getting the carb ready to fire and see if it will turn the engine over or keep working to get a good blue spark before moving on? It just doesn't seem like there are as many parts available online as when I first started working on this tractor. I hope I don't run into any more surprises before I can see it running.

 

[scootergmc]

I just fitted my mag back onto my 70 a couple months ago and if I recall correctly, the mag drive on the engine wasn't perfectly horizontal/or vertical (I don't remember) when the flywheel was lined up on the correct mark. I don't recall the manual saying it had to be perfectly aligned but I can look again. My only issue is that I was 180 out on the internal mag gears once the mag was fitted. Just a bonehead move on my part.

As for the mag itself, I put a new condenser in and cleaned up the points and reset the gap. Parts can be scoured on eBay and the like. I have the luxury access to a test stand as well. After I did the work I had a bright orange spark rather than a weak yellowish spark. I never got to a good blue/whiiteish spark.

 

[Sturdily7974]

I already had new points and condenser, purchased years ago for way too much money. I took the magneto apart and cleaned it all up, re-greasing the bearings. I sparked a 12 volt battery across the casing, the only way I had to re-magnetize the core. Putting it all back together, the sparks looked to be more powerful this time. The last two plugs to fire, 2 and 4 cannot be seen. I know they are getting a spark because my father accidentally put his hand on number 2 when turning over the engine. For some reason the large gear with the white mark now lines up with the red dot instead of the raised tooth. I keep forgetting to take pictures.

I could purchase a new coil (SM137) easy enough but I still cannot find a new brush and spring. I found some brushes from some other parts laying around and tried to grind them down and put a spring on one. The first spring was too long and didn't work but I managed to get one working. Perfect? I don't know but unless someone knows where an exact replacement brush can be found it will have to do.

I don't care about keeping the tractor original. I would replace the magneto or put a distributor and coil on it if I knew where to get one that would fit.

Right now I'm just going to get the carburetor and gas line hooked up and see what happens when I try to turn the engine over.

 

[scootergmc]

Don't bother with fuel yet. Spin it it over and give it a little shot of starting fluid. No point bothering with the fuel system if you haven't resolved ignition. You won't know whether you're chasing fuel or spark if you start monkeying with fuel before establishing spark.

I would reset the mag to the correct position, reset the tractor to #1 TDC using the mark on the flywheel (and I like having the valve cover off to watch and see when it's coming), and try again. If the mag is timed correctly and you have four of six, it's going to fire off. Are you using the (I'm assuming new) plugs to check for spark or are you checking from wire to top of plug/block? Did you clean your connectors, both inside the mag at the plugs?

 

[Ken Grimm]

I already had new points and condenser, purchased years ago for way too much money. I took the magneto apart and cleaned it all up, re-greasing the bearings. I sparked a 12 volt battery across the casing, the only way I had to re-magnetize the core. Putting it all back together, the sparks looked to be more powerful this time. The last two plugs to fire, 2 and 4 cannot be seen. I know they are getting a spark because my father accidentally put his hand on number 2 when turning over the engine. For some reason the large gear with the white mark now lines up with the red dot instead of the raised tooth. I keep forgetting to take pictures.

I could purchase a new coil (SM137) easy enough but I still cannot find a new brush and spring. I found some brushes from some other parts laying around and tried to grind them down and put a spring on one. The first spring was too long and didn't work but I managed to get one working. Perfect? I don't know but unless someone knows where an exact replacement brush can be found it will have to do.

I don't care about keeping the tractor original. I would replace the magneto or put a distributor and coil on it if I knew where to get one that would fit.

Right now I'm just going to get the carburetor and gas line hooked up and see what happens when I try to turn the engine over.

I have a couple used distributors and drives and a couple new ones too if interested

 

[Ken Grimm]

I have a couple used distributors and drives and a couple new ones too if interested

And a 70 id sell

 

[Sturdily7974]

I finally got to see a spark on all 6 wires. I checked next to the mag so I could see it while I was turning it over. I was relying on someone else to tell me if it sparked before, so who knows if they could see it. I had a couple of different spark plug testers and the one that worked the best was the Oregon one. Turning it over manually, I saw a spark on each clunk of the magneto and using a screwdriver with a paint mark, made sure each one was hitting at the top.



You can see the white marks match on both gears when number 1 is at the top. Currently the large gear in the magneto is lined up with the red dot on the small gear. For experimentation: I set it one tooth back, which would line the white line on the large gear up with the raised tooth on the small gear. This would put the white mark on the large gear just ahead of the window on the mag cover. Got a spark all the way around and the pistons were all where they should be. The manual specifically talks about a red marked tooth so I'm going to leave it unless the engine tells me otherwise. Red tooth or raised tooth, I don't know which is right. You do have to attach the mag to the tractor with the raised tooth pointing straight up or it won't align and mount up. The oliver manual never mentions a raised tooth that I can find. Both teeth will fire them all off.

I did polish out the inside holes on the mag cover, so maybe that helped. Now I need to check for a spark at the plugs. I switched wires around and spark plugs and 2 and 4 were not firing that anyone could see. Could be they were sparking on the back instead of the front and nobody could see it.

When setting the spark plugs on the edge of their holes touching metal, they should all spark when turning the engine over. 2 and 4 cannot be seen. Yet now I know they are firing because I saw the sparks in the tester. I'll keep playing with it but I think I can say my magneto is in working order, even with my custom built parts.

 

[Sturdily7974]

I have a couple used distributors and drives and a couple new ones too if interested

I may take you up on the offer some day, we'll see how it goes. You just can't find parts any more like you used to.

But no I don't want another tractor. =) This one's sat long enough.

 

[scootergmc]

You can see through your mag window, I'd be thankful. Mine's a cloudy haze. As long as you have the line/dots line up on the mag gears, you should be see the correct mark when it's mounted with flywheel in place.

Are you using new plugs? They're cheap enough I would.

 

[Sturdily7974]

Yep. New wires and spark plugs.

 

[Sturdily7974]

It's now lost it's spark again. Too weak to be seen in the tester so I'm giving up on the magneto.

 

[Sturdily7974]

Is this the best information available on switching from a magneto over to a distributor:

Oliver 70 - Yesterday's Tractors

I have a Oliver 70 that the magneto went bad and I replaced it with a distributor, it has lost a lot of power since I put it on. Does anytone know if

www.yesterdaystractors.com

 

[Ken Grimm]

I would think so