Project: Dual lighting coil SR stator into US KDX200

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TheRadBaron
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by TheRadBaron »

I don't really know about snowmobiles, but I don't think that Yamaha RDs were set up in that manner. They have two sets of points that fire each cylinder at different times (at least that's the way I understand it). Most other vintage 2-stroke twins that I know of are this way, also.
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Project: Dual lighting coil SR stator into US KDX200

Post by TheRadBaron »

I'm slowly making progress here. The first bit of news is that I took some measurements and it looks like the SR stator plate will be able to fit under the E-series flywheel with no problems. I took the measurements with the flywheel still on the bike so they're not super accurate, but it looks like it will work. As I reported earlier, the flywheel from the US-spec E-series KDX200 and the same years SR-model carry the same part number so I'm hoping that they are indeed the same part.
I would pull the flywheel off the bike and do a test fit of SR stator plate but I don't want to take anything apart just yet. My overall plan is to first verify the timing of the bike as it is now, in stock condition. This evening I located TDC using a TDC finder tool that threads into the spark plug hole and provides a positive stop for the piston by protruding down into the cylinder. To locate TDC you rotate the crank until the piston stops and make a mark on the flywheel at the position of the reference pointer on the engine case. Then you rotate the crank in the opposite direction until it stops again and make a mark. The exact midpoint between these two marks is TDC. I also found the midpoint between the two marks on the other side of the flywheel to indicate BDC. This will be necessary when I'm trying to determine whether the ignition fires the plug exactly every 180 degrees or not.
After I located TDC and BDC I used some swell geometry that I remember from school to figure out how to measure degrees on the flwheel. The flywheel is 112mm in diameter. Circumference is found using C=Pi x D, so 3.14159 x 112= 351.85mm. To convert that to degrees is 351.85/360= 0.977. So each degree is 0.977mm on the flywheel. I used some tape to measure out 10 and 20 degrees BTDC on the flywheel.
Image
My factory manual gives the ignition timing as 21 degrees BTDC at 6000 RPM. I have one of those hour meters that also functions as a tach so hopefully that will actually work and tell me RPM. I plan to use an inductive timing light to take a measurement at idle and every 1000 rpm until 6000. I know that the bike runs well as is so this will give me a good baseline as to what the ignition timing is doing. Once that is done I'll remove that piece of tape and make another one for BDC and perform the same tests to see what's happening at and near BDC. Once I determine all these things I'll hopefully be able to continue on to the next steps. Does my scientific method seem sound here?
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by chkdx »

I think you're right on target.

Just make sure your timing light isn't one of those "dial back" ones where you turn a dial on it until the timing marks on the flywheel are at zero, then you read the timing on the dial. Those kind are notoriously inaccurate at anything above a slow idle.

I assume your timing light is just a simple inductive one with no dial. Those work fine.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by newbbewb »

to find out if BDC is same as TDC, your research sounds great, kudos.

Rambling: I would imagine that the CDI changes dynamic timing somewhere do to compression changes inherent to the 2 cycle engine. I could be wrong, but my guess is somewhere around 5k the CDI timing will change.

This reads out bad, but why exactly do you care whats happening at BDC in order to make the sr stator work?
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by chkdx »

This reads out bad, but why exactly do you care whats happening at BDC in order to make the sr stator work?
This is explained earlier in the thread.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by adam728 »

TheRadBaron wrote:I don't really know about snowmobiles, but I don't think that Yamaha RDs were set up in that manner. They have two sets of points that fire each cylinder at different times (at least that's the way I understand it). Most other vintage 2-stroke twins that I know of are this way, also.
You are right. Its the upgrade units like Zeeltronics that utilize waste spark.

I've been looking at a lot of the RD stuff trying to decide what to do on my old CS5 (RD200 predecessor).
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by adam728 »

chkdx wrote:I think you're right on target.

Just make sure your timing light isn't one of those "dial back" ones where you turn a dial on it until the timing marks on the flywheel are at zero, then you read the timing on the dial. Those kind are notoriously inaccurate at anything above a slow idle.

I assume your timing light is just a simple inductive one with no dial. Those work fine.
We have a MAC and a SnapOn at work that are the "dial back" type. There's some calculations made by them based on rpm and the degree reading that determines when to flash the strobe. Both hate >5,000 rpm. They will double the timing after that point, ie, if advance is 25 degrees at 8,000 rpm you actually need to set the timing light to 50 degrees to align the TDC marks.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by TheRadBaron »

adam728 wrote:
TheRadBaron wrote:I don't really know about snowmobiles, but I don't think that Yamaha RDs were set up in that manner. They have two sets of points that fire each cylinder at different times (at least that's the way I understand it). Most other vintage 2-stroke twins that I know of are this way, also.
You are right. Its the upgrade units like Zeeltronics that utilize waste spark.

I've been looking at a lot of the RD stuff trying to decide what to do on my old CS5 (RD200 predecessor).
That's interesting. I wasn't aware that those aftermarket ignitions were wasted spark. That might suggest that there is indeed an advantage to having a 2-stroke fire near BDC. Someone should ask Kevin Cameron.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by fuzzy »

If wasted spark was not utilized on multi-cyl engines a distributor would be needed. Probably more 2-strokes are wasted spark than not.
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TheRadBaron
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by TheRadBaron »

fuzzy wrote:If wasted spark was not utilized on multi-cyl engines a distributor would be needed. Probably more 2-strokes are wasted spark than not.
That's true for a 4-stroke but not necessarily a 2-stroke. Since a 2-stoke fires every revolution there's no spark to waste. That's true for multi-cylinder 2-strokes as well. A BDC spark could be added if desired or if it somehow simplified some aspect of the design, though.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by TheRadBaron »

Also, the wasted spark on a 4-stroke generally happens near TDC on the exhaust stroke, not BDC like we're talking about.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by bufftester »

As an engineer I like how this is taking on it's own life as a science project :grin: I'm still not convinced KDX's run a wasted spark, there's no compelling reason for it from a design standpoint (you would actually be making the process more complicated). Keep in mind that the CDI does retard the ignition at around 6k rpms to acount for the KIPS valve opening (IIRC KDX timing curve is 6 BTDC at idle up to 21 BTDC around 6k, then once the KIPS opens the timing falls back to 6 BTDC) A lot of discussion has been made about tuning the KIPS opening rpm, ideally you want it to match exactly when the CDI retards otherwise you're just inefficient. Anxious to see some results.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by Jaguar »

I know all about KDX CDI's and can tell you for sure that they don't produce two sparks per revolution.
Click on my signature link to see a timing graph for the KDX CDI.
Performance CDI -- KDX motocross mods -- the SR KDX -- expansion chamber analysis---> http://www.dragonfly75.com/moto/
TheRadBaron
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Project: Dual lighting coil SR stator into US KDX200

Post by TheRadBaron »

I spent the last few hours out in the shop working on the KDX and I have some very interesting findings. First I used my inductive (non dial-back) timing light to get a baseline of the timing curve. I wasn't able to get a tach hooked up so I just sort of went by sound. The timing on my bike is steady at 21 degrees BTDC at a high idle up to near redline when it pretty quickly retards back to around 10 degrees. This sort of corresponds to what bufftester said a few posts back. The main difference is that my bike is at 21 BTDC at an RPM just above idle. If I slow the idle down low enough that the bike is struggling to stay running I can see the timing start to retard.
With that knowledge I took off that piece of timing mark tape and put it at BDC. Turns out that my bike does NOT fire the plug near BDC or anywhere else other than the main ignition firing near TDC. Only one spark per revolution.
I then installed the SR stator plate and stock US-spec flywheel. I lined up the timing mark on the stator plate just like I would have on US-spec plate. The SR plate fit under the flywheel with no problem so that potential snag can be crossed off the list. I took the plug out of the bike grounded it to the motor using a wire with a clamp on each end. I did this so that I wouldn't risk any damage to my motor if the timing was way off when I tried to start it. I put the timing tape back on the TDC mark and I was able to kick over the bike while pointing the timing light at the flywheel. To my surprise, the spark was still taking place at TDC. I put the plug back in and gave it a kick. The bike seemed to be kicking back a bit more than usual so I was thinking that the timing might be advanced a bit. Dude541 noted the same thing when he put an SR stator and flywheel on his KDX220. After a few kicks the bike started and sounded fine. I shot it with the light and found the timing to be about 25 degrees, so it was indeed advanced. I popped the flywheel back off and got the timing correct. I started the bike again and revved it up to check the timing curve and found that it was still identical.
Hmmm. So even though the source coil is 180 degrees off and the ignition does NOT spark every 180 degrees, the plug is still firing at the proper time. I guess this takes me back to my original question about what, exactly, signals to the CDI that it's time to fire?
Next, I compared the SR and US-spec source coils and noted that they were different. The SR coil is taller. The mounting bolt holes are the same, though. Just for the sake of science, I put the US coil onto the SR plate and put everything back together. Timing was still spot on. So whatever signals the CDI to fire must not be the source coil, at least in this instance. I feel like I must be missing something obvious but I really cant figure out what the signal is.
I haven't ridden the bike yet but everything points to everything working perfectly fine, at least as long as the ignition system is concerned.
So in summary:
-The SR stator plate is basically a direct bolt-on for the E-series KDX200. Only minor timing adjustments are needed to get it dialed in and they're well within range of the adjustment slots on the plate. Minor wiring changes will also be needed. I'll get to that later.
-The SR and US-spec flywheels are identical, and the taller coils of the SR plate fit under it just fine.
So this is all good news, even though I don't quite understand exactly what's going on :?
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by chkdx »

Very interesting! Now you've got me wondering why my engine seemed to have a waste spark, hmmm. Next time it's running (in the process of building hybrid now) I'll have to recheck it.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by bob_jones »

@TheRadBaron How did things turn out with this? Does the bike run well / normal and all that? Any changes? How do the electrics perform etc? Thanks.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by TheRadBaron »

Everything works great. The bike runs brilliantly and all of the lighting works properly. I actually haven't ridden it very much with the BD kit on it. Both headlight bulb filaments broke with about 100 miles so maybe a more robust bulb is called for. I never did ride the bike at night so I can't really report on how well the headlight lights up the road/trails. Sorry for the lack of good follow up info.
All of the work I did dual-sporting my KDX ended up being kind of a waste because I decided to de-emphasize its DS use in favor of making it a more hard-core race bike for hare scrambles. All of the wiring and stuff is still in place so it wouldn't be a big deal to convert it back over to street legal and I probably will strap it back on at some point this year for a DS ride or two. I was planning on getting a different bike for DS use but I've had a few financial setbacks so I'm not sure that it's in the cards this year. Oh well, the KDX is a great platform for a hard-edged DS bike and it won't hurt my feelings to use it for another year.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by bob_jones »

That's great! So, you said that the SR stator was basically a direct bolt-on replacement but you said minor wiring changes would be needed but that you'd "get to that later"... were those wiring changes to the stator?
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by TheRadBaron »

Hey, sorry for the very delayed response. I guess I missed the notification that a reply had been posted.
Anyway, the minor wiring change that I did to be SR stator was just to float the grounds on the two lighting coils. I won't bother explaining the basic process since it's easy to find in a search, but it's simple to do. The same procedure is used on the dual-coil stator, you just have to do it twice. I soldered another wire onto each coil and ran both of these new ground wires through the grommet and up to where the rest of the stator wires make their connections. I put both wires into the same crimp terminal and mated it to the BD lighting kit.
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Re: Project: Dual lighting coil SR stator into US KDX200

Post by bob_jones »

Excellent thanks very much!
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