Ironhead Magneto removal and reinstall drop in?

[Todd007]

Hi. First post. I’ve lurked here a while now.

I have a 1970 XLCH motor with magneto and need to replace the oil seal. I understand how to set the advance, static timing and so forth but … if I marked the alignment of everything, can I lift out the mag, install the seal and mount and drop it back into place, without re-setting advance, timing etc? Thanks. T.

[Ferrous Head]

Yes, you can.

Sometimes it's a little bit "hit and miss" but I have done it many times.

I set the engine at it's firing point (45 BTDC) on the narrow lobe before I pull it out.

When you pull the magneto out it will turn due to the worm gears driving it. But that's OK. When you replace the magneto it will reverse it's direction as it goes back in.

If you have not moved the magneto shaft while it was out you should have no problem. If it goes back in but the timing is now advanced or retarded by a significant amount (it will be obvious - it's like 12 degrees or so) then you are a tooth out. You need to pull the magneto out again and move it slightly in the required direction.

[Monte03]

Ferrous gave a great reply but why would you Not check ? Assuming you will have the Cap off and will be checking the points , checking that both Lobe Gaps are at .015 on the lobe NOSE , checking that the skinny lobe ( front cylinder ) points just start to open .. * adding some oil down into the Cams helps a bit with the re installing gear mesh

[Captain Johnny]

Knowing that everything must be right for a magneto bike to start and run, why would you not check piston position, set the points, drop it in then static time?

Agree with the first 2 posts.

[Todd007]

Thanks all. I likely will/would check but having not removed one I was curious if it could be done that way as I couldn’t see why not. T.

[Ferrous Head]

Guys, he knows about timing the mag. But if you have never pulled a mag or a distributor before you just want to be sure you can get it all back correctly.

I understand how to set the advance, static timing and so forth

Smart man to ask questions if your unsure.

[Todd007]

Originally Posted by Ferrous Head

Guys, he knows about timing the mag. But if you have never pulled a mag or a distributor before you just want to be sure you can get it all back correctly.


Smart man to ask questions if your unsure.

Exactly. I always get a bit stressed and don’t want to find myself off the road unnecessarily because of some error or misunderstanding. (I have service and parts manuals, but as you know, they’re not always the best or sole reference.)

[Monte03]

Originally Posted by Ferrous Head

Guys, he knows about timing the mag. But if you have never pulled a mag or a distributor before you just want to be sure you can get it all back correctly.

—— Exactly why he should check everything with the magneto cap removed , why go through all that, install the carb, try to fire up then find its not in time? plus you learn, many just do not see the point in the Roll of the Dice method
Smart man to ask questions if your unsure.

[rejeanprimeau]

Mark the position with a felt pen and voilà, just realign the marks.

[Ferrous Head]

OK.

It can be a little frustrating sometimes. The magneto shaft doesn't just spin smoothly like a gearbox shaft. If you take the time to spin a magneto y hand you quickly see what I mean. The magnets inside the magneto makes the shaft want to only sit in discrete locations. What this means in practice is that the shaft will move slightly when you pull it from the mating hear on the cam shaft.
So, you often drop the magneto back in what seems like exactly the correct position only to find your a tooth advanced or a tooth retarded. Just pull it up and move the head approximately one tooth's worth in the required direction.
It can be sort of trial and error but just persevere. Sometimes it drops in first go.

By having set the ignition before you do this and having the cam in the magneto in a known position it's easy to tell when you have it on the right tooth.

It's much easier to show someone how it's done compared to typing in a description.