GY6 Flywheel Comparison (11 Pole Upgrade) By jstluise (Read 13,728 times)

[jstluise]

I am currently in the middle of the 11 pole upgrade for my 2009 Kymco Agility 125 (GY6). Slowly but surely I have been making progress with help from John (tvnacman) and others over at Scooter Doc. I purchased the parts from John, who has also sold the same parts to other riders for successful 11 pole upgrades on their scoots.

There was question of whether or not the new flywheel I bought would cause ignition timing issue or not since the location of the trigger magnet (in relation to the key way on the flywheel) was different between the two. Here is a picture showing the Kycmo flywheel (left) and the replacement (right):



As you can see, the location of the trigger magnets are very different. We suspect that there will be timing issues since the CDI relies on the trigger to know the rotation of the engine; changing the location of the magnet will obviously change when the trigger signal is sent to the CDI. The trigger should occur when the engine is at TDC, and this will not be the case with the new flywheel.

Another issue was whether or not the old flywheel would work with the new 11 pole stator. Both flywheels contain 8 magnets (see video below), and after measuring, the inner diameter of the flywheels are the same. Given that, we don't foresee a problem with using the original Kymco flywheel in the upgrade, even though everywhere you read online states that an 8 pole flywheel is different than 11 pole flywheel. Also, the Kymco flywheel has stronger magnets, which will result in better performance.

Just wanted to get this out there for everyone to see. I'm not sure why the new flywheel is different...the Kymco is either a different breed (though I thought all GY6s were mostly the same), or there was a manufacturing mistake with the flywheel.

I would love to hear (as I'm sure John would too) any thoughts regarding this issue. I'm making progress on the upgrade, though just found out I need to get a AC CDI since Kymco uses DC CDIs, so that has slowed my progress.

Here is the video showing the two different flywheels and their magnets (I show the Kymco first, then the replacement):

[JR]

Jstluise I read all the debate on Doc and so since you came here to ask I'll sort it out from all you've been told.

The 11 magnet flywheel if it even exists is rare. Some people order from parts sellers and then get the flywheel only to discover it's still only 8 magnets so on that myth put it to rest, the 11 pole stator will work find with a 8 magnet flywheel. Many have installed a 11 pole stator on the typical GY-6 and never changed the flywheel including myself. The Kymco GY-6 is generally the same as any other GY-6 other than better bearings and the crank, and it looks like the stator also. Why? Simple they want you to buy Kymco. No need to worry about the firing of the CDI on it because it's simple.

Lay your old stator out exactly like the position it is mounted on your scooter. If need be draw a straight cross of lines on a piece of cardboard or very this sheet metal for a template put it on the scooter with a hole in the center so the crankshaft will go through and then make reference holes on the template for how the stator bolts on.

Then place your old stator on the template and mark a center mark of where the CDI pick up coil is. Then place the new stator on the template and compare. If the new stator pick up coil lines up with the old mark then you're good to go use the old flywheel . If not then you've got to do this;



Using your template spin the new stator pick up coil to line up with the mark of the old stator and drill new mounting holes in the new stator. This can be done but simply put it's got to be dead on to make sure the stator is centered well or it'll rub or not be lined up properly with the magnet. I have done this.


Some stators have multiple mounting holes for different applications, some don't?


Stronger magnets, not enough to really make any difference on your charging because charging output is controled by the regulator if you remember and the stronger magnets will not be noticed for this reason alone.

Now the grand debate on the CDI? The "myth" of a DC type CDI is better is just that, some swear by the "the scooter starts better in cold weather" Own both systems AC and DC and IMO it's hogwash. But I will say this when you are stranded with a dead battery you'll love the AC type CDI so you can get home with a kickstarter and saying it'll run off of the R/R power is iffy, some will some won't and you've forgot one thing that hasn't been mentioned in this debate at Doc.

You've got to wire in a 7-pin R/R the old R/R you have will not work and since you now have a AC type stator for a AC type CDI that will keep you going with a dead battery why not take advantage of it?

Advantage you say? Yep if you're riding down the road and the R/R goes out the battery will be down to under 11Vdc in a very very short time. Why? DC powered CDI will suck it down in less than 20 miles. A DC powered CDI WILL NOT fire at less than 11 VDC.

The AC type CDI/stator system could care less if you have a battery or R/R when it comes to running the engine. Means a lot when you want to get home even with a dead battery.


Guys I'm going to be gone for the day will check back in tonight.

JR

[tvnacman]

JR , you make some very interesting points above . DC CDI using hight current stealing from the charging system . The AC CDI has it own power coil isolated from the charging system . So charging problems and battery voltage has no effect if the engine will run .

Sorry JR I don't see how the cdi effects cold starting , if spark is present with fuel , with a well adjusted valve train . The scooter should start without trouble . I could see on a cold day with a low charge or weak battery a DC CDI not firing .

In short I like the ac cdi ignition , it is only dependent on the coil from the stator , the cdi itself and the coil and the plug .

John

[jstluise]

Wow thanks guys for the help! Very good stuff!

Aug 4, 2012 5:25:36 GMT -6 JR said:

Lay your old stator out exactly like the position it is mounted on your scooter. If need be draw a straight cross of lines on a piece of cardboard or very this sheet metal for a template put it on the scooter with a hole in the center so the crankshaft will go through and then make reference holes on the template for how the stator bolts on.

Then place your old stator on the template and mark a center mark of where the CDI pick up coil is. Then place the new stator on the template and compare. If the new stator pick up coil lines up with the old mark then you're good to go use the old flywheel . If not then you've got to do this;

Could you explain this a little more? I am confused because you are making reference to the pickup (trigger) coil when talking about the stator, and they are independent of each other (as far as mounting goes).

Are you talking about the independent coil on the stator that is used for the CDI? If that is the case, I don't understand why the location of the matters. For that matter, I don't understand why the position that the stator is mounted in matters at all; all we care about are the magnets passing over the stator coils. Unless one of the flywheel magnets must be precisely over one of the stator coils at a certain position of the crankshaft (TDC?), then I could see there being an issue, but the adjustment is small since there are 8 magnets on the symmetric flywheel...I guess you have a 45 degree adjustment angle (360/8).

There must be a relationship between the stator coil, flywheel, and trigger coil that I am not aware of.

Also, remember my original Kymco stator doesn't have an independent coil for the CDI because the Kymco CDI is DC.

Using your template spin the new stator pick up coil to line up with the mark of the old stator and drill new mounting holes in the new stator. This can be done but simply put it's got to be dead on to make sure the stator is centered well or it'll rub or not be lined up properly with the magnet. I have done this.

If this needs to be done, I'll pop it on the mill at work; I'll have more precision that I'll probably need.

Now the grand debate on the CDI? The "myth" of a DC type CDI is better is just that, some swear by the "the scooter starts better in cold weather" Own both systems AC and DC and IMO it's hogwash. But I will say this when you are stranded with a dead battery you'll love the AC type CDI so you can get home with a kickstarter and saying it'll run off of the R/R power is iffy, some will some won't and you've forgot one thing that hasn't been mentioned in this debate at Doc.

I have to agree I saw mixed responses about the AC vs. DC CDI. I AC CDI makes sense for the reasons you mentioned and I'm sure I won't notice an difference between either as far as performance goes. I do have to say I was in the situation of a dead battery with the scoot cold...there was no way I could have kick started it (I tried..a lot). I have kick started it without a battery, but the scoot was warm. So it is possible...just not easy in some situations.

You've got to wire in a 7-pin R/R the old R/R you have will not work and since you now have a AC type stator for a AC type CDI that will keep you going with a dead battery why not take advantage of it?
JR

Yep, I got the 7-pin R/R from John. I have no questions about it and the wiring is straight forward. Right now it was just the flywheel/CDI situation we were dealing with.

I like the benefits of the AC CDI...especially since it runs off its own stator coil; I can imagine the DC CDI sucks a lot of juice out of my system before...this would be an issue since I want to run an extra lamp on my scoot (won't be an issue with the 11 pole stator).

Thanks again! John will be sending me an AC CDI soon so I can running. Please let me know about the stator mounting position questions that I posed above.

[tvnacman]

I missed the USPS today it will go out on Monday .

John

[JR]

Could you explain this a little more? I am confused because you are making reference to the pickup (trigger) coil when talking about the stator, and they are independent of each other (as far as mounting goes).

Are you talking about the independent coil on the stator that is used for the CDI? If that is the case, I don't understand why the location of the matters. For that matter, I don't understand why the position that the stator is mounted in matters at all; all we care about are the magnets passing over the stator coils. Unless one of the flywheel magnets must be precisely over one of the stator coils at a certain position of the crankshaft (TDC?), then I could see there being an issue, but the adjustment is small since there are 8 magnets on the symmetric flywheel...I guess you have a 45 degree adjustment angle (360/8).

There must be a relationship between the stator coil, flywheel, and trigger coil that I am not aware of.

You answered your own question and sorry I did mean the trigger coil.

I'm fully aware of the fact the kymco does not have the independant coil for AC power to the CDI but it does have the trigger coil and a seperate magnet like in your picture to pass by the pick up coil when the piston is at or extremely close to TDC. If the magnet is not placed in relation to TDC then the scooter will pop, misfire and act stupid.

So if you take your old stator and put it back on and make a reference mark to where the triger coil is and then put the flywheel back on, turn it by hand, line up the single trigger magnet and then check the piston will be at TDC. Also remember the CDI fires on both the compression and exaust stroke.

So now with the old stator in place put the new flywheel on and do the same thing, turn it until the single trigger magnet lines up with the pickup coil and then check to see if the pistion is TDC if so then it's a-ok then put the 11 coil stator on and the old flywheel and go for it, I'm betting it's not.

Now do the opposite, put the new 11-coil stator on, make a reference mark and put the new flywheel on, line the trigger magnet with the trigger coil and check TDC. Then slip the old flywheel on with the new 11 coil stator and do the same, you'll get your answers on timing then with no guess work.

Like I said Kymco does things different on purpose, a typical Chinese 11 pole stator is plug and play on a typical 8 coil Chinese scooter but by your pictures it says the Kymco is not a typical Chinese stator set up.

I ran into this on a Malaguti scooter a good time back and a guy bought a 12 pole stator off of ebay that is on a few scooters out there like some BMS ones and when he got it he discovered his error but we made it work by re-drilling the mount holes to make it line up at the proper time to fire in relationship to the piston timing.

Now here's another thought since you have access to a mill and good machinery you could slot the bolt mount holes on the new 11 pole stator and could advance or retard the timing by turning the stator ever so slightly?

Just a thought.

JR

[jstluise]

Before I respond to your entire post/instructions, I think I need to gain a better understanding how the stator/flywheel/pickup coil work together. It seems I am confused with some terminology and how the engine timing is accomplished.

Aug 4, 2012 20:56:24 GMT -6 JR said:

You answered your own question and sorry I did mean the trigger coil.

I'm fully aware of the fact the kymco does not have the independant coil for AC power to the CDI but it does have the trigger coil and a seperate magnet like in your picture to pass by the pick up coil when the piston is at or extremely close to TDC. If the magnet is not placed in relation to TDC then the scooter will pop, misfire and act stupid.

So I was using "Trigger Coil" and "Pickup Coil" interchangeably because I thought they were the same thing, but from the sounds of it they are two separate components....? I thought trigger/pickup coil was referring to the coil mounted outside of the flywheel which sends a signal to the CDI when the trigger/pickup magnet (which is mounted on the OD of the flywheel) passes by it

It sounds like you are saying the "Trigger Coil" is a coil on the stator, and the "Pickup Coil" is the externally mounted coil to signal to the CDI. Is this correct? I've looked at the Kymco 8 pole stator and all the coils look the same to me...

My understanding was this: the stator simply supplies AC power to the R/R and CDI (in Kymcos case, just the R/R, which gives us DC for the CDI). The flywheel has a pickup magnet mounted on it so that when it passes by the pickup coil, the CDI gets a signal at that point of the cranks rotation (TDC). The signal tells the CDI that the engine is at TDC (or close to it), and the CDI adjusts the timing based off the engine speed.

As far as the stator having any influence on timing, I don't see it. In between fires, the capacitors in the CDI are charged via the stator, but rotating the stator's mounting position will only change what point in time the CDI is charged (in the AC CDI case). I'm curious, but I doubt it takes one full rev (in between fires) to charge the CDI. If it does take exactly one full rev (8 magnets passing over the CDI charging coil), then the position of the stator must be precise...but still, this has no effect on timing, just charging for the CDI.

What really drives it home for me is to think about the DC CDI setup. First, the CDI receives constant power (DC) for charging the capacitors, thus the mounting location of the stator has no effect on the power supply to the CDI. Second, from just looking at how everything is wired up, the only communication with the CDI is power (DC from the R/R) and the pickup coil...nothing from the stator. This tells me timing is only controlled by the relationship between the pickup magnet and the pickup coil.

Basically, I just need to know how it is possible to retard/advance the timing by rotating the mountain location of the stator. I am missing something. The only way I see to retard/advance the timing is to move the location of the pickup magnet that is mounted on the flywheel. In my case, I am using the original flywheel with the new 11 pole stator, so I don't foresee having any timing issues.

Obviously you have encountered this problem before and rotating the stator was the solution, so I just want to know why. I really appreciate all the help! I always like to learn!

[JR]

OK let’s start over and clear our heads and get on the same page and then I think it can be understood how it works so let’s take it all one thing at a time.

Now the CDI and lets use the AC type because you must remember the new 11 pole stator you want to use does have a AC coil that has one purpose and that's to send power to the CDI so it can store it build it up and then send it to the coil. It sends it through the single black/red wire. You are correct on the Kymco and the DC type CDI the stator has no such coil because it is fed from the battery. So that's simple enough.

So now here is where I think the confusion comes in (me I was born confused) Both flywheels the new one and the old one have the pickup coil magnet or trigger magnet on the outside of the flywheel just as you have their location marked in your pictures above. With the keyways of flywheels located in what I will call the 12 o'clock position it obvious in your pictures that the trigger magnet on the OEM flywheel is in the 2 o'clock position.

So your original 8 coil stator mounts on the engine and the outside trigger coil magnet or pick up coil in the position that is timed in a way that when the flywheel trigger magnet passes around it sends the signal or pulse to tell the CDI to fire and that's it. It has nothing to do with the voltage being sent to or stored in the CDI. It simple says fire when the piston is at TDC on the compression stroke.

So as you mentioned in all of this will the new 11 coil stator flywheel be in timing with the engine? First let’s look at your picture and see the location of the trigger magnet on the new flywheel and it's in the 9 o'clock position.

If you go to the tech section and look at the pictures of the 11 coil install you'll see that changing out the 8 coil to 11 coil on the standard GY-6 is easy because you use the OEM flywheel and then trigger coil is the same and even the AC coil is in the same location.

But your origianal question was will the new flywheel work and will it be in timing with the Kymco engine and my answer is no. The trigger magnet is in a different location in relation to the OEM trigger coil/flywheel.

I'm sorry about the slotting and redrilling on the stator thing I forgot on this engine the stator is not on a mounting plate with the trigger coil on the same plate. The trigger coil is mounted in the same place on this engine no matter what stator you use.

We did have a scooter once that used a back mounting plate and this is the one we put the 12 coil stator on and we had to relocate everything.

But like I said it would be easy to check the new stator flywheel especially since I've cleared my head a little. Just slide it on the shaft, line the trigger magnet up with the pickup coil and the check the location of the piston. Pull the plug and put a soft wire in the hole and turn it by hand utnil the pistion stops at TDC and then look at the location of the trigger magnet.

I hope this clears this up and again I'm sorry for any confusion, it's been a difficult week for me I just laid my mother to rest and just haven't been myself.

I don't think you'll have any issues at all with the new stator and the OEM flywheel.

JR

[jstluise]

Thanks, JR. I'm sorry to hear about your mother...my condolences.

We are on the same page now after your clarification. The biggest thing that cleared the air was this:

...I forgot on this engine the stator is not on a mounting plate with the trigger coil on the same plate. The trigger coil is mounted in the same place on this engine no matter what stator you use.

For the life of me I could not see how rotating the stator would change the timing, UNLESS the trigger coil was mounted on the same plate as the stator. Then it would all make sense.

You are right that the new flywheel will cause issues because of the new location of the pickup magnet. Using the OEM flywheel is the way to go.

I think we can call this problem solved. I will respond with an update once I get the new CDI and everything wired up.

I do have one question that may deserve another thread, but its quick. Does the housing of the 7-pin R/R need to be grounded (via the mounting bolts)? The reason I ask is I found a good spot to mount it (since it is so big compared to my other R/R, it won't fit in the same spot), but it involves mounting it to plastic, instead of metal like the old one. If it does require grounding, I'll have to make a ground strap to go from the mounting bolt to a spot on the frame.

[JR]

Yes the R/R has to be grounded and thank you for your kindness. When I went to the 11 pole stator upgrade in the tech section I realized then that this scooter didn't have the mount all backing plate like the one we did with the 12 pole stator upgrade did.

Like you said with the trigger coil in a fixed position the stator mounting is illrevelant.

JR