1980 Honda CB750 Alternator Rotor Replacement

Replacing the alternator rotor on a 1980 Honda CB750f motorcycle. Not intended as an instructional video, it is part of a video catalog of our restoration project.

[@brianmaragos]

rittercon, you have no idea how much your video helped me today. I have a 1981 cb750k that wasn't charging. I tested the rotor and was getting 1.1 OHMs on my meter. My new (used) rotor came today and I couldn't get it off for the life of me. I ordered the puller with the part number you gave me and in 3-4 business days I will be rolling! Thank you SO much!

[@82cb900racer]

Very nice video. I've not had good luck with aftermarket rotors, but I was still able to buy one from Honda 2 years ago. Cost $500 cdn, but still working great after 30,000km. If you can't find a puller the thread chaser for automotive oxygen sensors works too. I have also taken the rear axle out and used it, but this is alot of extra work and the long axle bolt flexes quite a bit.

[@IrishWarCry11]

This video was a life saver. Thanks for taking the time to post it, you saved me a lot of time.

[@nandoGdog]

I needed one of those 22 years ago!

[@HTMR]

Nice vid! I uploaded a vid on my channel for the CB650, which rotor is on left side. I used the rear axle as a puller to remove rotor. Saved me $20!

[@rittercon]

So happy that the video helped you. I am not a pro, but have learned lots by watching KZbin videos. Thought I would do my own contribution. Regards-

[@rittercon]

Try pulling the # 3 spark plug wire, attach it to a loose spark splug and then ground the plug threads to the motor at some spot where you get a good ground. Make sure the bike is in "neutral" gear, turn on the ignition and crank the motor. You should see a spark emanate from the plug head (center electrode) to the end electrode ("L" shaped metal piece at the end of the plug).

[@rittercon]

I got my last one online from Rick's Motorsport Electrics. New ones are $180 us and rebuilt are $205 us. The rebuilds use a heaver gauge wire, which they say is the reason for the higher cost.

[@rittercon]

My new Rick's Motorsport rotor showed 3.6 ohms resistance between the two slip rings on the rotor. Rick's told me that they use a heavier wire than OE rotors, which causes a lower reading (typically 3 - 3.5 ohms). OE rotors usually show between 4-5 ohms.

[@rittercon]

The stator, which doesn't move, wraps around the rotor, which does move. You can see both at minute 1:50 in the video. The Stator is on the left, inside the alternator housing. The rotor is on the right, attached to the crankshaft. FYI- rotors go bad a lot more often than stators. Test your rotor as shown in the video at minute 2:00 (bad rotor) and again at 7:20 (good rotor).

[@rittercon]

Thanks. I muffed around a bit before I finally figured how to get the rotor off. Yes- that's the stator inside the cover. I did replace the rectifier/regulator; the connections were severely corroded and I wasn't getting the correct response to the tests.If you need the tool, I'll loan it to you, although it's not too expensive to buy. Mr. Bookout (commenter below) has it now and I thinks he's probably finished using it.

[@rittercon]

I bought the first rotor from Electrosport, but it failed after about 2 weeks. I got another from Rick's MotorSport Electrics and it has worked fine. Both companies are online. By the way, Rick's uses heaver gauge wiring than the OE rotor from Honda- it has lower resistance and supposedly works better and lasts longer. You might try that. Good Luck

[@brianmaragos]

so i got my puller and i couldn't get it off. Then I realized the bike was in neutral, lol. Put it in gear, whacked it 3-4 times, and voila! Off and charging! Thanks 100x!!

[@rittercon]

The Stator should have between 0.4 Ω and 0.5 Ω resistance between any pair of yellow wires and no continuity between any yellow wire and ground. Some rewound stators have been found to be higher in resistance, closer to 1 ohm between any pair of yellows, and still work fine. Stator voltage - measure AC volts between any yellow to any yellow wires on Alt/Stator connector (~8 to 15 VAC) while the engine is running at a respectable RPM

[@GustavoGarica]

Thank you soooooo much !

[@ronsullivan1045]

no special tool needed ,rear axle does the job

[@brymilan]

You make this look easy! Inspires a lot of confidence in a motorcycle maintenance noob like myself. You even have the same multimeter as me. :) I think I may have to do this to my 1980 cb750k. It's not charging the brand new battery that's in it. That's the stator inside the cover, correct? Also did you replace the rectifier/regulator?

[@rittercon]

Yes, they did. They sent me a replacement rotor, but it also failed after 3 weeks. They then refunded my money. I have no complaints against Electrosport, as far as customer service is concerned.

[@bhills73]

thank you

[@rittercon]

If no spark, try replacing the #3 wire with a different one (doesn't need to be new for this test). If still no joy, the issue is in the ignition, not the plug or wire.

[@TheBetaMale]

I need to replace the rotor on my 83 Nighthawk 750. I've pseudo-rewound the rotor by recoiling on top of the old winding but it seems that I used too small of a gauge. I'm going to try with a larger gauge and potentially rebuilding the rotor properly. Where did you get your rotor from? I was wondering in case my cheap fix fails and I need to simply buy a fresh one.

[@1977Gunslinger]

You got to whack it!!! love it!

[@handyman7297]

which book are u using for ilustration on minute 4:15..? a clymer one or honda service shop repair manual?

[@rittercon]

I can't say for sure, but you might want to test your regulator/rectifier. The R/R converts the alternating current from the alternator to direct current and regulates the charge to the battery at 14.5 volts with 1-3 amps. I'm not sure how many raw amps the alternator puts out; 7 might be OK

[@glara619]

Can these rotors be rebuilt? Thank you fir the helpful video. Great information.

[@markbookout1497]

Can u use a screw with the same tread and deminsions vs the puller I'm on a very tight budget

[@markbookout1497]

This dude is great and VERY HELPFUL! Please subscribe to him.

[@nathanhale7001]

WARNING. I followed the video and my alternator came loose in 600 miles destroying my new alternator, stator, brushes, and brush plate (a new brush plate is really hard to find since Honda discontinued it). SOLUTION: Get Blue Loctite and a torque wrench. Cover the threads with Blue Loctite and torque the bolt to 70 ft. lbs. I've had no issues in 3,000 miles. The bolt tightens in a clockwise direction and the crankshaft also turns in a clockwise direction which means with the engine turning clockwise, that motion is constantly trying to loosen the bolt. You can test by using a ball point pen. Hold the top of the pen facing away from you in left hand by thumb and forefinger and hold the bottom/tip of the pen in right hand using thumb and forefinger. Now, turn the top of the pen clockwise (crankshaft rotation) while holding the tip of the pen where it cannot move. The pen will unscrew itself. With the constant spinning of the crankshaft clockwise you MUST use Blue Loctite on the bolt threads and I recommend you set the torque at the higher end (70 ft. lbs.) of the recommended scale (58 - 72 ft. lbs.) or you could have a disaster like I suffered.

[@rittercon]

Thanks for the warning, Mike. Good info.

[@bhills73]

awesome video thank you, about how much did it ccost and where did you get it from, i think i need one on my 81

[@wil0099]

Thats probably true but mines an 82 cb750sc and the rear axle worked for me and the guys at Milwaukee cycle parts. Thats where I got my rebuilt rotor so if this one fails in time I will have to get a new one from Honda. Its apparently a dealer part.

[@Cigaristocat]

Hi! Can you tell me if the fairing that covers the rotor is supposed to get hot while running? I had problems with mine before where it was shorted to ground and did not generate so I'm afraid it might have been caused by the heat. Let me know if you can. Thank you.

[@rittercon]

Mine gets hot. Don't really know if it's internally generated or absorbing the engine heat.

[@Cigaristocat]

rittercon Thank you for the answer! I've made a gasket for the cover so I hope it is enough to reduce any heat transfer from the engine itself.

[@glara619]

Man this first bolt is a pain in the butt!!!

[@mtrcycls]

"I couldnt wack it and hold on to the camera...." lol

[@s.h.1527]

Where did you get all your parts? I have a 1980 cm400t that needs a new alternator and i can't seem to find one. I'm new to bikes and don't know where to look

[@rittercon]

Try Electrosport and Rick's Motorsport Electrics. One of the video viewers also recommended Milwaukee Cycle Parts.

[@Lude34]

Did Electrosport honor their 1 year warranty? Is the $30 price difference between the two worth it? Thanks

[@elwoodwilliams4604]

Easier if you put the back wheel on the ground, put bike in gear. Then you can remove & tighten the nut w/o engine rotating.

[@bhills73]

Have you noticed a difference with the higher gauge wire?

[@iviaverick52]

The alternator has to be torqued down to 60-70 ft lbs. How do you recommend doing that since it's freely spinning?

[@rittercon]

The manual states: "If necessary, use a strap wrench to keep the rotor from turning while removing [or attaching] the rotor bolt, or shift the transmission into gear and hold the rear brake on."

[@markbookout1497]

I ask cause from the video and what I can find online picture wise it appears like a simple hollow bolt

[@rittercon]

The Clymer manual. The part number (07933-4250000) is on page 197 and the picture (Figure 11) is on the next.

[@rittercon]

Yes, they can. I've heard Jim Parrott does a very good job on rebuilds; his site is tpe-usa.com. He'll rebuild yours or sell you a rebuilt one for about $90. I know some folks rebuild their own, but I'm not one of them.

[@rittercon]

No difference that I can perceive, other than it works fine.The rotor shows 3.6 ohms resistance between it's two copper slip rings, meaning it has somewhat less resistance than OE rotors, which usually show between 4-5 ohms.

[@wil0099]

Check out Milwaukee Cycle Parts they sell rebuilt ones and so far I havent had any trouble. They ask for a exchange which will save u 50 bucks if not they sell for $229.00

[@rittercon]

Yes, it's a bolt. I'm the nut...

[@richhartman5350]

I got some really go stuff off KZbin

[@vientosnomadas3668]

en español seria bueno

[@User6327]

Bolt. Not nut... :)

[@chrisg6ekd451]

Ever heard of a torque wrench? Misuse of a wood working hammer! No gasket.

[@lokotron1]

why didnt you just smacked the bolt instead of getting a special part for it?

[@rittercon]

+lokotron1 The threads on the rotor are larger than the oem bolt, so the oem bolt just passes through the rotor and screws into the crankshaft. You want a bolt (larger size than oem) that screws into the rotor and presses against the end of the crankshaft.This puts pressure between the rotor and the crankshaft. When you whack it, it's enough of a shock to dislodge the rotor from the shaft it's pressed on. The end of the special part is tapered, so it fits nicely against the crankshaft. A regular bolt might work, as long as it screws through the rotor and presses against the crank, Just be careful the end of the crank doesn't get damaged, or you may not be able to get the oem bolt back in.

[@lokotron1]

what about smacking without the bigger bolt? just on the surface of the rotor, once the oem bolt is removed?

[@rittercon]

+lokotron1 I don't think you want to directly hit the surface of the rotor, as it may push the rotor even tighter onto the crankshaft and possibly damage the crank. You need some way to apply tension between the rotor and the crankshaft. Remember, it is a "pressed" fit and needs tension to "un-press" the rotor from the shaft.

[@lokotron1]

i get it.. seems like i need that screw

[@rittercon]

+lokotron1 I had one and loaned it to a KZbin viewer, who promptly "lost: it...

[@rittercon]

I would think as long as the threads match, and you can "bang" on the end, it should work. I know that some people use the rear axle off of certain models. I'll loan you mine if you promise to send it back. Send your address to me at (rittercon at yahoo dot com)

[@richhartman5350]

I got some really go stuff off KZbin