Fitting later model ignition system to 1975 Johnson 115

[powerabout]

I went out and bought a better multimeter yesterday which can measure AC voltage in mV range and has max and hold functions. I'll put the '75 model ignition system back together and see if I can troubleshoot more accurately this time.

I will still probably change the system over though unless my no spark issue turns out to be something simple. Powerabout, if you can upload a photo of a mounting suggestion at some point i'd really appreciate it.

As far as compatibility of the bearing carrier, there was no numbers written on the older motor. But I looked up the part number for "Crankcase Head and Bearing Assy" and the part numbers are the same for both motors. The top of the assembly does look different between the motors though - there is an angled shoulder on the newer motor whereas it is squared off on the older one - see photos. I assume it should still work?

I worked out that I should be able to use my original harness and just relocate the kill wire from the terminal style powerpack on the 75' model to an unused position on the terminal block (looks like it will reach ok). If I unravel the harness from the newer motor and take the kill wire that goes to both plugs for the power packs and also connect it to this same position on the terminal block it should just require the mounts for newer packs and coils and take off old pack and coil assembly. Easy to change back if it doesn't work!

Older crank:
Attachment 498109

Newer crank:
Attachment 498110

Juswt put the sensor assembly over it and see that it is free to move.
You will still need a DVA adapter in a std multimeter to read peak volts

[Gilera]

I just tried the trigger and it does bind on the top of the crank. I guess there goes my idea of transplanting the later system and back to troubleshooting my own.

[powerabout]

I just tried the trigger and it does bind on the top of the crank. I guess there goes my idea of transplanting the later system and back to troubleshooting my own.

So the diameter of the bearing surface is different on each of the crankcase heads/bearing carriers?
How about swap the end caps, you can put a new bearing them.

[Gilera]

Not the diameter but the height of the recessed area inside the trigger. It hits the top of the upper crank bearing housing. I thought about swapping them over but after I undid the 4 bolts I couldnt get it off. Is there a trick to it?

[powerabout]

Not the diameter but the height of the recessed area inside the trigger is 20mm. The height of the top of the crank housing is 20mm. I thought about swapping them over but after I undid the 4 bolts I couldnt get it off. Is there a trick to it?

You might have to loosen the crankcase half bolts at the top.
Hopefully it hasnt been glued in.

[Gilera]

This bearing carrier is STUCK. Tried undoing crankcase bolts and heating it up. Levering up from various different points. Looks like just an o ring under it - do they normally come off pretty easily if not glued on?

[Gilera]

I got a new battery 100ah yesterday as my old one was dying. Engine spins very quick now. Still I was only able to get a weak yellow spark and only when the plugs were out.

[Gilera]

Not sure if anyone is following this but i finally got the bearing carrier off the 1980 model 85hp. There is one threaded hole in the back of the carrier to the right. Its that same thread size as the 4 bolts that hold it in. I took one of the bolts and ground down the head so it would fit in the head of my slide hammer. It took a bit but it finally came off. I then used the same technique for the 1975 model which came off alot easier. Next step is to fit all the electrics from the newer motor and see whether it works. Any advice on how to mount the power packs and coils would be welcome!

[Gilera]

That was short lived excitement. The other bearing carrier doesn't seem to fit in the housing of my 1975 model. Must be just the tiniest bit wider so you can't get it started. I could try chamfering the bottom edge below the first O ring with some sandpaper?

[Gilera]

Tried chamfering the bottom edge without success. The current replacement part numbers are the same for these two motors so I guess the diameter should be the same. Perhaps just variation from the factory. I can put the original bearing carrier back in my 1975 ok and it will slide down into the housing, but can't get the 1980 model one into it. I read in the factory manual that when reassembling the motor you normally put this "upper crank assy" in before bolting the crankcase together. I could try to remove the top bolts as advised to remove the stuck one but that was a seized motor that I didn't care about. If I do this i'm worried that I run the risk of the crankcase not sealing anymore.

[powerabout]

Tried chamfering the bottom edge without success. The current replacement part numbers are the same for these two motors so I guess the diameter should be the same. Perhaps just variation from the factory. I can put the original bearing carrier back in my 1975 ok and it will slide down into the housing, but can't get the 1980 model one into it. I read in the factory manual that when reassembling the motor you normally put this "upper crank assy" in before bolting the crankcase together. I could try to remove the top bolts as advised to remove the stuck one but that was a seized motor that I didn't care about. If I do this i'm worried that I run the risk of the crankcase not sealing anymore.

If the part numbers are the same then where the sensor coils run must be the same?

[Gilera]

If the part numbers are the same then where the sensor coils run must be the same?

That's what I had thought before I tried to swap them. What it seems like is that the original part for the 1975 model 0385504 has been replaced with the original part number for the 1980 model (0387432). Given the difference in shape I can see how the earlier timing base would be compatible with the later bearing carrier but not vice versa. My photo in post #15 is not the best but if you look carefully you can see that there is more of the shoulder cut away in the later model. The shoulder of the earlier bearing carrier is what interferes with the inside top of the later model timing base.

There is no difference underneath but you can see some deep scoring in the one I got from the 1980 model seized motor.

Off 1975 motor:


Off 1980 motor:

[powerabout]

That's what I had thought before I tried to swap them. What it seems like is that the original part for the 1975 model 0385504 has been replaced with the original part number for the 1980 model (0387432). Given the difference in shape I can see how the earlier timing base would be compatible with the later bearing carrier but not vice versa. My photo in post #15 is not the best but if you look carefully you can see that there is more of the shoulder cut away in the later model. The shoulder of the earlier bearing carrier is what interferes with the inside top of the later model timing base.

There is no difference underneath but you can see some deep scoring in the one I got from the 1980 model seized motor.

Off 1975 motor:


Off 1980 motor:

Can you take a photo of the top sides

[Gilera]

Don't know why the photos ended up upside down. The white one is the later model.

[Gilera]

Well I managed to get the later model bearing carrier in at least for testing purposes. It needed a bit of careful sanding to fit. Unsure if it was a result of the engine it was fitted to destroying itself or variation in tolerance from the factory. I made some brackets for the power packs. They look a bit asymetrical but i used aluminium angle and wanted it to sit flush with the original mounting points for the single power pack so that they would be more rigid. They feel very secure. The mounts are a bit different on each side. I could mount 2 coils in the original place for the 3 bolts coils that were on the '75 model, I could use one hole for the other 2 coils but made mounting plates to angle the other 2 in a way that fits. I still need to route the wires better and will replace the bearing carrier with a better one if I can find one as it has been knocked around and the bearing might not be the best. Anyway I turned it over and managed to get good spark from all 4 cylinders jumping a 7/16" gap on my spark tester!