Results 1 to 8 of 8
  1. #1
    CB750 Enthusiast leo750k's Avatar
    Join Date
    Jul 2019
    Location
    central florida
    Posts
    33

    battery not charging

    Discovered today that my battery is not charging, I have a manual, and haven't started going thru the list yet,
    was wondering if anybody had any advice on what to start with first? I was thinking maybe the brushes on the stater coil?
    thanks for any advice

  2. #2
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,569
    One of the most common early DOHC fails...............the rotors. They can check as good and still be bad too. Lots of trouble with the rebuilt ones too. The stator and brushes are relatively reliable unless brushes are simply worn out. The rotor going out commonly ruins the regulator too.

  3. #3
    CB750 Enthusiast leo750k's Avatar
    Join Date
    Jul 2019
    Location
    central florida
    Posts
    33
    just got done measuring the resistance on the rotor, 1.5 ohms plus or minus a tenth, bad rotor?

  4. #4
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,569
    Thinking the spec is 4.4 ohm or something like it. Lower resistance is often a good thing but there it is a BAD thing. Shows the layers of wire are shorted and what they do. Many of the ebay ones are bad too FYI.
    Last edited by amc49; 10-22-2019 at 09:18 PM.

  5. #5
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,569
    Here we go................service manual spec. 3.6-4.4 ohm. Nothing outside of that number and they can be bad inside the range there too.

  6. #6
    CB750 Enthusiast leo750k's Avatar
    Join Date
    Jul 2019
    Location
    central florida
    Posts
    33
    Have you known of anybody that has successfully rewound one of these coils themselves? doesn't seem that it would be too hard, IF you knew the wire dia,and number of wingdings. I have a good friend that is a chemist in the semi-conductor industry, he could spec. the potting compound for me.

  7. #7
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,569
    It's harder than you think, the wire coating glue (an epoxy) down job has to be done through the entire wind, surface of the outside only is nowhere near enough. You need a winding machine unless you wind the core and then mount it on the two split halves of the rotor and then you are faced with whether that went back together tight enough. Try winding a core with all the moving in and out to avoid the touching of the rotor wings which with one scratch through the paint insulation scraps the whole job and you'll know why they need a machine to do it or wind the core separate and then you have to make sure it also mounts in tightly enough and glues down well enough the inertia of running never tears the core loose from the rotor iron. Then it needs balancing there at 10,000 rpm and where to do that? The choice of the paint coating on the wire can kill you by itself.

    Now you see why the rebuilders themselves have such utter fits getting them right and they DO have fits, and many still go bad very quickly anyway. Even Honda could not make them last. I lost my first one at 3000 miles.

  8. #8
    CB750 Enthusiast leo750k's Avatar
    Join Date
    Jul 2019
    Location
    central florida
    Posts
    33
    Quote Originally Posted by amc49 View Post
    It's harder than you think, the wire coating glue (an epoxy) down job has to be done through the entire wind, surface of the outside only is nowhere near enough. You need a winding machine unless you wind the core and then mount it on the two split halves of the rotor and then you are faced with whether that went back together tight enough. Try winding a core with all the moving in and out to avoid the touching of the rotor wings which with one scratch through the paint insulation scraps the whole job and you'll know why they need a machine to do it or wind the core separate and then you have to make sure it also mounts in tightly enough and glues down well enough the inertia of running never tears the core loose from the rotor iron. Then it needs balancing there at 10,000 rpm and where to do that? The choice of the paint coating on the wire can kill you by itself.

    Now you see why the rebuilders themselves have such utter fits getting them right and they DO have fits, and many still go bad very quickly anyway. Even Honda could not make them last. I lost my first one at 3000 miles.
    "whether you think you can, or whether you think you cant, Your are Right"
    but I dont have any way to balance it, so that is a deal killer. thanks for your input

Similar Threads

  1. Best Battery For 79 CB750K?
    By rs_ss350 in forum The CB750 Garage
    Replies: 6
    Last Post: 01-26-2016, 02:54 PM
  2. What is this tube next to battery?
    By George1285 in forum The DOHC Garage (1979-1983)
    Replies: 5
    Last Post: 11-25-2015, 10:48 PM
  3. Battery Help
    By CivilPenny in forum The CB750 Garage
    Replies: 2
    Last Post: 07-15-2015, 11:16 AM
  4. Battery Not Charging / 'Cold' Weather Starting
    By Gergify in forum Electrical
    Replies: 1
    Last Post: 06-17-2015, 07:56 PM
  5. Ballistic Battery
    By aeromech in forum The CB750 Garage
    Replies: 4
    Last Post: 05-29-2014, 12:28 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •