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me again flywheel issue 425 magnum 4x4


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I also have a magnum 4x4 that I am working on it is getting a new piston, In the tear down I pulled off the flywheel

and found that all the magnets are not attached? why does this happen? there all in good shape so is it possible

to reattach them to the flywheel? I can buy a different flywheel, but it looks like around $300 or more and one of them on Ebay

looks like the spacing is off a little so it may have the same issue.

the stator looks good also 

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That sounds like badly made really.. Can you see how they were held in ? Some bikes the magnets are glued in and some have some sort of clip or blocks of hard rubbery stuff between the magnets holding them in.. I've seen cases where on magnet was loose.. but never the whole lot.

I don't think I'd try repairing it though.. to much potential for real damage if they came off again, smashed the stator, broke, and went through the engine.

Perhaps there is a problem with them.. and perhaps there is a superseded part.. I'd check the genuine parts supply, and check for warranty or recall info....

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I know nothing about this bike, I got it tore apart with the piston stuck in the jug, but it came with a used jug and a new piston and rings.

it's a 96 with 112 miles on it, well that is what the odometer says it's a 4x4 with real good plastics with nice tires my best bet though would 

be to find a new engine for it I think that I would have less money into it going that route, because I am not sure of the parts that I am missing now

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I was talking to my son last night over a beer, and he reckoned that if they are dry flywheels, the magnets come unstuck from sitting around.. he's had then deteriorate sitting on his parts shelf(my shelf really !).

He reckons rust creeps in if they get cold and wet.. poor little things..


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If the pistons stuck because of sitting it might be ok.. usable even.. If it seized from overheating and then got parked.. not so much..

Soak it is something.. diesel even does a good job.. then pound it (the piston) a bit with a wooden hammer handle, or solid dowel and hammer (one pound).. It'll come free.. Free the rings in their grooves carefully then take them out and and clean it all and put that top end back together.. It will be good enough to test the rest of the bike.. Then you decide whether to do more repairs or not..

That's what I'd do.

Ah.. Gwbarn beat me to it..

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  • 1 month later...

Just for grins I might try to start it just to see what it does, maybe check the compression, sometimes the rings will free up, soak them with carb cleaner, and PB blaster that will take care of the rust and dried gas residue. Make sure valves are not stuck turn over slowly before starting.

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You're not likely to get much compression if the rings are stuck. I'd work the rings free starting at their gap and levering the two ends apart a little with a tiny screwdriver, then once the ends start moving out, if you use a plastic screwdriver handle to tap the rings back into the groove while the screw driver is still in the gap you'll find that the ring lifts out of the groove a little further around. Then use a bigger screwdriver to lever the ends apart further and repeat the tapping so the ring lifts even further around the piston. If you keep spreading the gap, and then tapping the ring back into the groove while the rings ends are held apart you'll find they come free. Work  the tapping from the gap along towards the stuck place. Once they move you could take them off and clean the grooves, or if they seem to free up nicely then just give it a good clean. Oil the rings and put it together and it might come right. If the bore isn't grooved then I'd just clean it. If the bore has alumiium stuck to it then I use caustic soda on a small brush or rag and apply it to the stuck aluminium. Caustic eats aluminium but not the cast/steel so you can avoid honeing the bore which will upset the rings being run in, and cause more wear as they re run in. You need to apply the caustic in a really well ventilated space and stand up wind because it produces some really exceptionally toxic fumes.. I mean the fumes will have you choking from twenty feet away even outside if you are down wind. Because the caustic has such a violent reaction with aluminium it's important not to get it anywhere except on the aluminium in the bore, don't try dropping the whole bore into a bucket of caustic or you'll end up with just a steel sleeve left..

The caustic is really handy if you have a bore that's nitro hardened and which won't hone. I've recovered two stroke motorcross cylinders that had been proclaimed beyond reuse by bike shops using caustic. 

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  • 3 months later...

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