Magneto ignition rotation?

[ian redshaw]

Hi folks.

A question for the more knowledgable. Basically, I have need to reverse the rotation of a magneto ignition. The flywheel and coil is now on the back of the engine so in effect is running in reverse. Basically the cylinder has been turned round 180 degrees and the original coil mount is used. So, I know I'll have to retime the flywheel but will the coily sparky bit still work as the magnets will effectively pass from the opposite direction??

Ian.

[David Brown]

That's a good one Ian, never tried but thinking on the Z38 probs people have had and posted on this site where they run backwards, I would think that it must work in reverse.

Dave

[ian redshaw]

Cheers for the reply Dave, it helps to confirm what others have said elsewhere, but it pays to ask!! This conversion is for the back cylinder of an inline twin, the front cylinder stays as standard. My second option would have been to mount another coil opposite the one mounted for the front cylinder, but that wouldn't be the ideal solution as it'd be a somewhat chunky front end to the engine! I know the easy route would have been two electronic ignition units but they are the work of the devil to a simpleton like me.

Ta again,

Ian.

[Cary Bailey]

Ian, the pick up determines when the ignition is to operate, therefore provided the pick up & magnet are in the correct "position" relative to where the piston firing point is, (x degrees before TDC)there is no problem. What you may have to address is if the ignition has an in built retarding system which is used for starting purposes as the "curve" used for one direction may not work when reversing it.
If the magnet cannot be repositioned you can always install the pick up on a "sliding" bracket that allows the pick up to be adjusted to get the correct degree for ignition timing.
Cary

[Andy Macqueen]

thats correct, most strimmer/chainsaws run in the opposite direction to our use so they will run never the less as long as timing is set accordingly,its much easier with an electronic ignition to do but as long as the mount for the mag pickup is close to the flywheel and timed, it will not matter.
what motor is it? you could always cut a new keyway in the flywheel rather than move the pickup.

[ian redshaw]

Cheers for that conformation Andy, cutting a new keyway is the plan for the back cylinders flywheel. The other option would have been mouting another coil on the front flywheel, but the former is a much neater solution in my case.

Thanks folks.

Now the next question, where does a new keyway go in the flywheel??!! I wouldn't know but my solution is simply to hold two flywheels back to back (or front to front, whichever is easier) and physically transfer the difference (magnets to keyways etc) from one to the tuther, that sound about right??

Ian.

[David Brown]

Does it need to be keywayed ??? if its only there to spin & not drive the prop then the taper should hold it with a little locktite to assist.

Dave

[Peter Clare]

I seem to remember that some of the old two stroke motorcycle engines did not have the flywheel keyed. I suspect the keyway is only provided for ease of assembly on a production line. The key is only likely to shear if it experiences a high shock load or serious backfire.
Go easy on the Loctite - a taper fit plus a strong grade of Loctite could turn out to be extremely permanent!

[ian redshaw]

Thanks folks. I think I'll redo the keyway though as it will ensure it gets assembled with the right timing. I imagine it might be a bit of a ball ache trying to set it otherwise. I'm going to do the keyway this lunch time hopefully. The way I see it, if I get two flywheels and sit them back to back, carefully lining up the two (4) magnets, then I can mark one keyway off of the other one through the tapers? That is giving me the correct reversed timing isn't it??

Here's hoping!!

Ian.

[Andy Macqueen]

Hi ian,
Im not sure what motor it is but i would say nearly all ive come across will use one,more so if its a mag because of the pottential to backfire when starting,although the taper will be a tight fit it will prevent you having to re time it if it does backfire/strike as it will spin easier.
best way ive found to do this is put the engine at tdc,and mark on the flywheel where the pickup is and measure round to the start of the first magnet,a fabric measuring device will work best(dont tell the missus) and repeat the distance appart when flywheel is reversed, be sure to check where the pickup will actually sit on the rear and get the correct distance to the magnet at tdc!
this will get you very close,if you need to be 100 percent sure you can always check with a strobe on a mag engine but you wont be able to do it with a cdi unit as the shielding will mask the signal.
hope this helps