update to engine dies

by Marc Hawley in 2 Stroke Technical Questions 14 years ago

:( Up date on previous ... After sorting out broken wire,a couple of days later the engine would not kill with mag switches, same side was giving post ignition!
Opened the coil and fly wheel housing as thinking that coil kit is faulty!
To my suprise I found that the magnet on fly wheel had broken in 2 places,seems that something has come loose or foreign object got between the field coil and ring magnet and gauged out some magnet and pieces were floating around in coil!!!!
Have inspected the coil kit and found nothing missing or loose? replaced fly wheel with a 503 unit and all well,fired up first time.
Any ideas?
Marc

Re: update to engine dies

by bill martin » 14 years ago

bill martin

10 757 0

Hi Marc,

If you're lucky, something came loose in the case or got in the case from outside (not likely). Worst case is that this problem sometimes is caused by a bad crank bearing on the mag end. You might want to pull the mag cover off, have someone turn the prop by hand and see if you can detect any sideways movement at all in the crank. Check the two screws in each pickup module. if they loosen or come out the pickup and magnets can contact each other.
That stator is very expensive to replace if damaged.

The post ignition is not uncommon if for some reason the plug is not firing at the top of the stroke. The plugs in both cylinders normally fire at the top of the stroke and also at the bottom of the stroke. This is no problem when everything is working as it should. The reason for firing at the top and again at the bottom of the stroke is to eliminate the need for a distributor in the ignition system. When the plug for some reason doesn't fire at the top of the stroke, it will leave unburned fuel in the cylinder which will sometimes fire at the bottom of the stroke. Post ignition won't damage anything, just makes strange noises.

If the bearing is bad, it can sometimes be detected by consistently low compression readings in that cylinder because the crank is flexing downward during compression stroke. You might want to pull the exhaust manifold or pull out the plugs and look in the cylinder for any signs of bearing parts on the cylinder crown. These are usually very small pieces of the cage that hold the ball bearings in place. I would also remove the carb and look in the intake port. Bearing pieces will often be blown back into the rotary valve. Look for scars or dings on the valve edge and the valve port. Bearings can go bad and still run for a while, but will without fail, eventually grenade the engine. Look also for oil leaks around the crank seal on the mag end.

Roger has a lot more experience with this than me, and can give you additional advice. I think it does deserve some serious detective work.

Bill.

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