Incorrect Stator / Rectifier (KZ750 LTD F1)

KZ Riders,

Some History (Skip if you just wanna get to the bike related stuff)

So I bought a 1983 KZ750 LTD (F1) back in 2009 or 2008, I can't really remember, but I always had charging issues with the bike. I posted here and received great advice and feedback on how to test that charging system. I did some of those checks and I found a lot of OTHER issues with the bike's wiring and decided that my need of a college commuter bike were not that great, so I parked the bike for the foreseeable future. I ended up taking the engine out and fixing some other mechanical issues with gaskets and seals over the years. Then along came my brother in law who wanted to step up to a larger bike and sold me his 2006 SV650 for basically nothing... impossible to pass up. Eventually I met my wife and sold the SV to help finance the engagement ring (Women! Always ruining our moto dreams!). New house and couple of kids later and I need a little project to do after the kids are asleep to relax with. The past few weeks I've been jumping back into getting the F1 back in running condition.

Here is the current question I have for you knowledgeable Riders:

It looks like somebody before me replaced the charging system on a 750 with one from a 440.

I've cross referenced the part numbers on BOTH the stator and Rectifier that are physically ON my bike and they are single phase systems from a KZ440 which does not match what the OEM part numbers should be. Wiring diagram for the 750 shows a 6 wire rectifier and a 3 phase stator. I'm not sure if this was causing some of my issues, but I do know that the KZ440 stator looks significantly smaller with less "windings" around the circumference. I'm wondering if the voltage output was correct, but it just couldn't keep up amp/power wise. In any case, I've been looking at Electrosport to get a replacement rectifier and stator, but I see that the image shown for the ESR140 (It is listed as being an OEM replacement for what SHOULD have been on my bike from the factory) shows a 5 wire rectifier. I've reached out to see if the image is representative of the product, but my MAIN concern is with the rotor that is on the bike and it matching up if I replace the stator to the Electrosport one.

How can I tell if the rotor on the bike is a 440 vs 750? Diameter difference?
Any rotor differences between single vs 3 phase systems?

Thanks for reading! I'll post back if I find an answer to my questions in the meantime. I apologize if this has been addressed before, but I've been way out of the KZ Rider loop for the last 9 years.

As far i can investigate

The 440 LTD two phase stator is a 12 coil unit
Rotor has one magnet ring with one gap





The 750 LTD three phase stator is a 18 coil unit
Rotor has four magnets with gaps between them





Both rotor diameters unknown

All sources Evil-bay and Google

I assume the F1 is an inline four motor, and not the twin.

The main issue is the stator diameter as it matches the flywheel. I'm surprised to hear a 440 stator would physically bolt onto a 750 cover. Hopefully someone with a 750 can measure a spare stator to get the outside diameter measurement.

Electrically, a 1-phase stator can use the same flywheel as a 3-phase stator, (on most Kz lines), as long as the physical dimensions don't interfere. (This is only in regards to permanent-magnet alternators.)

There 12 magnetic poles in the flywheel/rotor. 6 north and 6 south. Mathematically they work out for either the 3-phase(18-pole) stator or the 1-phase(12-pole) stator. The physical magnets may be in fewer sections. I usually see 3 physical sections on the 550's, and i think on the 440 as well. Scirocco's photo does not show the sections clearly, but there look to be 3. A pole test will show 12 alternating poles.

A 750 alternator might have higher output than a 440 due to the extra ignition circuit and maybe more powerful headlights.

I would have expected an 83 Kz750 to be 3-phase with a 6-wire regulator/rectifier combo unit. Some earlier Kz's in the 650/700/750 line were 1-phase with 4-wire reg/rec, or possibly 3-phase with 5-wire reg/rec, or each of those could have an additional wire called the "sense wire" because it senses system voltage. The most common ones are 1-phase with 4-wire reg/rec and 3-phase with 6-wire reg/rec. That extra wire is almost always brown on Kz's.

As a side note, 2-phase does not exist on kz charge systems. 2-phase does exist in industry, but 2-phase systems would require at least 3 wires. A 2-wire stator is 1-phase.

Thank you both of you for the information! I greatly appreciate it. The 1983 F1 was an inline 4, the KZ440 was a twin.

It is definitely a 1 phase Stator with 12 coils and a 5 wire rectifier, both from a KZ440. as verified by the part numbers on the components. The rotor has 1 gap, so it's also safe to infer based on the information you've provided that the whole of the charging system was replaced with a kZ440 one, Rotor, Stator, and Rectifier. The voltage output on the system when I tested it long ago seemed ok at the time, but as you've stated, the higher power headlight and ignition differences might have accounted for the issues I was having with the bike.

I will be upgrading the parts to what should be on the bike. Thanks again for the information!

To me the photo shows two other gaps (at the green arrows).

Magnets are very brittle so it's probably easier to manufacture and glue them in multiple pieces.

Since it has come up several times over the years, here is a diagram of the magnetic poles on the cup-shaped Kz rotor/flywheels.

I drew each pole as if it was made of two halves. Each "N" or "S" represents half of a pole. That was to illustrate the fact that each magnet-section end is a half-sized pole. When it is laid into the cup (flywheel), each magnet section is oriented so the half-pole at each end lines up with the same type (N or S) half-pole of the adjacent magnet section.

This is done for a reason. Because each magnet-section end is the same polarity as the adjacent magnet-section end, they push away from each other. This tries to expand the ring. The cup -shape of the flywheel holds the ring together. This means the magnets are naturally holding themselves into the cup. They are epoxied in place, but the natural polarity of the magnets is also trying to hold themselves in the cup. (Kind of ingenious, in my opinion.)

Notice there are at least two types of rotors. Those with 3 sections and those with 4 sections. It is possible that a magnet in the 4-section type can be installed backwards. This is not possible in the 3-section type. Having one or more sections reversed in the 4-section type would reduce the output of the alternator.

Some 650 alternators ('78 and '79 1-phase) have shown to have slightly lower output. They are of the 4-section type (presumably, along with the 700 and 750-four). I wonder if the rotor magnets were installed with the wrong orientation.

Kz550 uses the 3-section type.

This vid shows how to check the magnet poles. It's possible that a 4-section rotor (as found on the Kz650/700/750 can be manufactured incorrectly. But I have never tested or found one that is made wrong. I'm just mentioning it as a possibility for explaining why some 650 and 750 charging systems seem to be weaker than others.

All you need is a tiny high-powered magnet. Mark each side differently. It doesn't matter which end is N or S, they can be marked A and B etc. As you slide the magnet across the magnet face, it will flip on its own when it comes across a different pole. In between poles, it will stand upright.

You are just looking for 6 of one and 6 of the other, in alternating sequence. If there are more than 6 of either one (probably both), then one of the 4 sections may be installed backward.