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Old October 27th 15, 05:32 PM posted to rec.crafts.metalworking
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Default Mount a 2 stroke upside down?

On Tue, 27 Oct 2015 07:44:33 +0000, Charlie+ wrote:

On Mon, 26 Oct 2015 14:06:48 -0700, wrote as underneath


I just wonder if the ignition in a point-less system will work so well
if the flywheel rotation is reversed? With the points type magneto it
makes no difference but with the pointless type the system is optimised
with a mapped timed firing by potted electronic components built into
the coil assembly (hence the modern easy start 2-stroke systems) and the
coil can be much smaller and cheaper as the UHV is generated by
electronic circuitry rather than directly by the magneto. So- maybe the
mapping will not make the corrections in the right direction etc.? I
would anyway try running it in reverse with an electric drill etc. to
see how the ignition might work if you do this?! Just a thaught - I
havnt tried so absolutely no actual experience with running this type of
ignition in reverse, someone else here might have?! C+

Thanks for the reply Charlie. It would be a good idea to see when the
spark occurs. If, for example, it happens at 12 degrees before TDC
then I need to make sure it happens on the other side of TDC since the
crankshaft will be spinning the other way. Using a drill to spin the
engine so I can watch the spark timing is a good idea. The electronics
for the ignition are located away from the engine, it appears that the
magneto coil is only a coil and has no device for sensing crankshaft
position, so all the timing is done in the black box that is mounted
away from the engine. But I still need to see what the timing is to
make sure I get it right when reversing the engine.

These modern pointless systems have two hall effect detectors (built
into the magneto coil system) to detect the speed of rotation and fix
the firing point in software ... and also by default the direction of
rotation I assume!! Your split box system I havnt come across - It must
still have the timing sense from the coil unit somehow, probably a
multiple cable connection to the cdi box. The modern ones only have the
plug lead and a kill switch wire, nothing else that shows externally...
I happened to have a modern chainsaw partly in bits yesterday so I
followed my own advice to you and span it in reverse with the ignition
on and watched the plug: correct direction, nice fat spark : reverse
direction, nothing... so be warned!!
I only ran it at speeds enough to get the spark to work properly and
then the same speed in reverse - no test to destructio!! No point in
wrecking a perfectly good chainsaw motor! If I were doing this I would
correct the position of the coil or the flywheel firing point AND also
turn the coil unit upside down so that it all works in the directions as
designed... maybe an oscilloscope and metalwork will be involved and
there maybe space problems! Could be interesting, keep us informed! At
full chat a high speed 2-stroke can be timed near 30 degrees BTDC I
believe! C+

I have a couple electronic points replacement modules made for the
typical lawn mower engine that used points. To use them the wire to
the points is cut and connected to the module instead of the points.
The only other connection for the module is ground. Anyway, these
modules work great and I believe the ignition on the engine we're
talking about works the same way. But I was wondering if the direction
the coil is wound in relation to the rotation direction of the magnet
would make any difference. Fortunately it looks like the magneto coil
can be inverted like you suggest. So if coil direction matters it
looks like I'll be OK.