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What would happen if you "Fixed" the mechanical advance

  • Thread starter Thread starter zacheriaj
  • Start date Start date
Z

zacheriaj

Guest
instead of letting it spin on the rotor, what if i just fixed it so it spins with only the crank shaft? Would it run just not as well? will it still throttle up?
 
I remember your thread of yours where the rotor seems to spin freely but did you figure out why this is happening? The rotor should only rotate when the weights move outward. It’s a very simple device. Is it a matter of the magnetic portion of the rotor coming loose from some sleeve? Please explain what’s wrong and maybe we can help.
 
Nessism said:
I remember your thread of yours where the rotor seems to spin freely but did you figure out why this is happening? The rotor should only rotate when the weights move outward. It?s a very simple device. Is it a matter of the magnetic portion of the rotor coming loose from some sleeve? Please explain what?s wrong and maybe we can help.
Click to expand...

Something broke and the weights dont move out. The rotor just spins without locking or moving the weights. I think there were metal tabs that locked onto the weights and allowed them to control when it spins. but now, it just spins freely on the whole mechanism. So in theory, when the engine is turning over, since the rotor spins freely, it would ultimatly stand still while the engine is turning over. Could i just fix the rotor to the whole mechanism so it spins with the engine? Or does it absolutely need the advance mechanism to run the engine?
 
You need that mechanism to work if you want your bike to run properly. Simply put, the faster an engine spins (up to a point) the more advance is required to ensure that the fuel is ignited at the ight time to develop power.
A pretty good example of what happens is on my wee PC50. There is no automatic advance / retard (in fact the only way of adjusting the timing is by altering the points gap). If it has too much advance (ie points too wide) it really struggles up hills; if it doesn't have enough advance (points gap too small) the top speed drops off dramatically.
 
The tabs that were originally there would "fix" the rotor to the crankshaft. It is supposed to turn at crankshaft speed.

There are actually a couple of parts involved in the advance mechanism. One part is attached to the crank and is driven by it. Another part has the magnets that will trigger the ignition sensors. And there are the weights. When the engine is turning, the magnets are also turning, providing a signal for the ignition to fire the coils. When you turn the engine faster, the spark needs to happen sooner, so the weights fly out, against spring tension, causing the magnet plate to rotate a bit, causing the spark to happen a bit sooner.

If your rotor is not attached to the crank, it will not cause a spark. If it has a little bit of tension and occasionally rotates, it might cause a spark or two, but they won't be at the right time. You definitely have to get this fixed for the bike to run, let alone well.

.
 
zacheriaj said:
instead of letting it spin on the rotor, what if i just fixed it so it spins with only the crank shaft? Would it run just not as well? will it still throttle up?
Click to expand...

There's something wrong with your description of the problem. Since we don't know what the exact problem is, it's hard to come up with solutions. If your mechanical advance is not fixed to the crank, it won't work. If you can (engine not running) rotate the mechanism, then it's not attached properly.

I can't imagine how it could be missing the alignment tab. That's a pretty stout piece of steel. I'd guess that you are missing a washer that holds it tightly in place...without that washer the advance assembly is sliding out on the shaft so it isn't seated and isn't spinning with the engine.

Maybe a better description of your problem is in order. Maybe even pictures
 
zacheriaj said:
instead of letting it spin on the rotor, what if i just fixed it so it spins with only the crank shaft? Would it run just not as well? will it still throttle up?
Click to expand...

The only time to permanently fix the position of the mechanical advance is on an engine that is not meant to run below 4000 RPM - ie. a racing engine. Even then, there's not a whole lot of good reasons to do it.

If something's not working right in your ignition/mechanical advance, read the manual, compare against the pictures, compare against the part diagrams, compare against a working bike if you can, think about it, and then _fix the problem_.

- Richard
 
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