Author Topic: Starter Problem (Read 2429 times)

Jim Harris · « **on:** November 29, 2020, 02:41:28 PM »

Good evening; I hope you all had a great Thanksgiving!
Did some annual maintenance on my 76 Honda CB750 today and ran into a starter problem. The bike is completely stock, everything ran fine before this work. I changed the points, the plugs, the condensers and replace the original 44 year old coils and plug wires with a new set, cleaned and adjusted the carbs and put everything back together.
When I tried to start the bike, the starter couldn't turn the motor over more than a couple of times before running out of power. All lights on and bright, over 12.8V across the battery. Thinking I must have run it down installing the points and other parts I tried a new battery and no improvement. Tested the started solenoid and got a nice click when I pushed the started button and read full voltage passing through on the multi-meter. My final thought was that the 44 year old starter motor finally gave up the ghost. Pull out the starter motor and tested it on the bench, to my surprise it jumped to life and spun like crazy. Could the starter motor still spin fast on the bench but just be worn out and not have enough torque to turn over the 750cc?
Thanks in advance for your help and suggestions!

69cb750 · « **Reply #1 on:** November 29, 2020, 02:47:05 PM »

Remove battery cables, clean ends.

scottly · « **Reply #2 on:** November 29, 2020, 07:41:02 PM »

What is the battery voltage when the starter button is depressed?

Jim Harris · « **Reply #3 on:** November 30, 2020, 12:05:39 PM »

Keeping in mind that the starter has been removed from the bike, so I'm using a test battery on the bench; I'm reading 10.5V across the battery when connected to the starter.

Bodi · « **Reply #4 on:** November 30, 2020, 12:53:49 PM »

The starter solenoid relay contacts get somewhat pitted and corroded but the unit can be disassembled and serviced. This is what usually causes weak starter action, and when it's happening a lot of heat is generated at the contacts... the solenoid can be destroyed if it's used like that for long.
Disassembly should be fairly simple and obvious. There's a copper bar contact that moves to bridge the inner ends of the terminal studs. Dress the bar with a file. The studs come out to make dressing them easier. Clean the end cap and internals, some dielectric grease where the bar slides helps it move smoothly.

seanbarney41 · « **Reply #5 on:** November 30, 2020, 01:50:27 PM »

When you replaced the points, did you know that point gap affects timing? Did you set the gap correctly and check the timing? Too advanced ignition timing can make the engine resistant to cranking.

Jim Harris · « **Reply #6 on:** November 30, 2020, 02:04:27 PM »

Yes, I set the points so the test light comes on at the exact center of the F notch in both 1-4 and 2-3.
I don't believe the points are the problem, they wouldn't be keeping the starter motor from turning over the engine. Even if the points were missing the engine would still turn over and try to start.

Jim Harris · « **Reply #7 on:** November 30, 2020, 02:08:57 PM »

In reply to Bodi...good suggestion about cleaning the contact points on the starter solenoid. I'll clean up the solenoid when I get back in the shop tomorrow and let you know if it makes any difference.
I'm also thinking about taking the starter motor to a rebuild shop to see if they can test it while its out of the bike, so we can rule that out and I can reinstall it to test your solenoid cleaning idea.
Thanks!

seanbarney41 · « **Reply #8 on:** November 30, 2020, 04:32:04 PM »

Quote from: Jim Harris on November 30, 2020, 02:04:27 PM

Yes, I set the points so the test light comes on at the exact center of the F notch in both 1-4 and 2-3.
I don't believe the points are the problem, they wouldn't be keeping the starter motor from turning over the engine. Even if the points were missing the engine would still turn over and try to start.

Hey, just trying to find some kind of cause and effect...old points, starter worked, new points and maintenance, now starter does not work...

HondaMan · « **Reply #9 on:** November 30, 2020, 05:19:56 PM »

When I rebuild these bikes I always take the starter apart, too, because the black carbon dust from the brushes builds up inside and can cause troubles when it gets to about the depth that equals the brushes wearing out. (That's about 4mm depth!). You can remove the 2 long screws that hold it together, then pull off just the rear cap: that's where the brushes live. See if their copper braid wires are touching the frames: if so, the brushes are worn out. About 25% of them i see are worn this much. New brushes are available from PartsNmore, Honda, sometimes CB750Supply, etc.

Jim Harris · « **Reply #10 on:** December 01, 2020, 08:06:27 AM »

Reply to seanbarney41 - Thank you sir for your suggestion about double checking the points, no harm intended in my earlier reply.

Reply to HondaMan - Since I have the started out anyway, I'll remove the starter mounts and check the areas you mentioned. Thanks for your help!

Jim Harris · « **Reply #11 on:** December 01, 2020, 01:45:33 PM »

Here's a photo of the starter motor we are discussing above. Again, the symptoms are, completely original, 44 years old, was working fine, but failed to crank over the 76 CB750 after some annual maintenance. I believe someone suggested cleaning the terminals and connections, which I will do. Does this photo look like it's due for a re-build kit?
Thanks for your help!

HondaMan · « **Reply #12 on:** December 01, 2020, 05:13:05 PM »

Quote from: Jim Harris on December 01, 2020, 01:45:33 PM

Here's a photo of the starter motor we are discussing above. Again, the symptoms are, completely original, 44 years old, was working fine, but failed to crank over the 76 CB750 after some annual maintenance. I believe someone suggested cleaning the terminals and connections, which I will do. Does this photo look like it's due for a re-build kit?
Thanks for your help!

The brushes look about average, 50% worn (not bad for 50 years, right?). If you have some brakecleaner, I'd suggest washing the area down (hold it downward to reduce the fluid flowing up inside where it takes a long time to dry) with some spray. This reduces the parasitic losses due to carbon filings making little short circuits here and there when the starter is sitting sideways in its hidey-hole.

Beyond that, it doesn't look terrible at all!

Did you get a look at your starter relay's contact bar? I have 2 that are toast. Both had symptoms of slow-turning starters. One of those starters was waist-deep in brush powder, with little arc marks burned into the inside of the case when I took a look inside. The brushes were also down to their nubs.

scottly · « **Reply #13 on:** December 01, 2020, 05:53:16 PM »

Quote from: Jim Harris on December 01, 2020, 01:45:33 PM

Again, the symptoms are, completely original, 44 years old, was working fine, but failed to crank over the 76 CB750 after some annual maintenance.

Sounds to me like you depleted the battery during your maintenance? Have you tried charging the battery? What type of battery do you have?

SquierA · « **Reply #14 on:** December 02, 2020, 11:53:18 AM »

Hey Jim,
I have a 1973 Honda CB500 and a 1973 Honda CB350F that are completely rebuilt with original starters in them and had the same issue with each bike. I purchased a starter rebuild kit on ebay for $15.00 and watched Common Motor Collective's YouTube video on how to rebuild a Honda CB350 starter motor and rebuilt the starter and they work perfectly now. Before doing this I was replacing the battery every year thinking the battery had failed and the entire time it was a worn out starter. Now the starter cranks fast and long and the bike fires up without draining the battery!

Jim Harris · « **Reply #15 on:** December 02, 2020, 01:19:32 PM »

Reply to HondaMan - 50% worn for almost 50 years sounds good to me too...I'll move on to washing down the armature, brushes, etc with brake cleaner, holding it upside down as you suggested, instead of rebuilding it at this point, then I'll reinstall the starter motor and focus my attention to cleaning the terminals etc. on the starter solenoid, replacing that if necessary, I can always pull the starter motor again if needed now that I've figured out how to get it out once, second time will be a piece of cake.
Thank you sir, you are a gentleman and a scholar!

HondaMan · « **Reply #16 on:** December 03, 2020, 06:36:19 PM »

Quote from: Jim Harris on December 02, 2020, 01:19:32 PM

...I can always pull the starter motor again if needed now that I've figured out how to get it out once, second time will be a piece of cake.

A hint: when you put it back in, wipe a tad of grease on that O-ring at the nose. I have put them in (too soon in the rebuild) to discover they got really STUCK the second time in(!).

Maltboy · « **Reply #17 on:** December 05, 2020, 05:57:57 AM »

Dumb question: I'm looking at the insulation on the brush wires on the right side, and it looks very worn where the wires bend down. Is a short in those wires a possible culprit?

Bodi · « **Reply #18 on:** December 05, 2020, 07:05:42 AM »

The wires to the "ground" brush are bare, the positive brush wires are insulated. These wires are very flexible to survive vibration but really don't move much. If the insulation is rotted and disintegrating you may get trouble but yours looks ok to me although pretty dirty. Rinse the whole area with brake cleaner to be able to see the insulation condition clearly. The wires - with insulation I think - come with replacement brushes. Your brushes are not close to being worn out but new ones aren't super expensive. Clean the commutator with a toothbrush and brake cleaner to get the carbon out of the grooves but it doesn't look bad enough to warrant pulling the rotor out for redressing, to me at least.
Personally I have never replaced brushes on a Honda bike starter... maybe because Canadian weather means bikes here don't wear out so quickly? I checked my 67 CB77 starter last year and the (original) brushes are like yours, worn somewhat but still good.
I still suspect the solenoid more than the motor.
And, off topic, I wonder how long the starters and solenoids will last on new vehicles that shut the engine off then restart at every stop and go?

Stev-o · « **Reply #19 on:** December 05, 2020, 07:18:20 AM »

Rolled my K4 out of the garage yester for a "Happy Hour" cruise and when trying to start, the starter motor would not turn off even with the key or kill switch! Never had that issue before. My first thought was disconnect the battery so I opened the seat and then it stopped. I then started it up and went on my ride no further issue. Odd. Carbon buildup within the starter?

MauiK3 · « **Reply #20 on:** December 05, 2020, 08:14:30 AM »

Back when I was building nuclear submarines the electrical guys that serviced the various motors and motor/generators would actually wash the rotors and bake them dry to get dust and carbon out of the windings. These were very large units, they had a very large washing facility.
I'm thinking the battery may actually be under par but still showing voltage, I had that problem.
The other thing is the solenoid, like others have said here, internally they may make connection but with high resistance.

Don R · « **Reply #21 on:** December 05, 2020, 10:59:58 AM »

Quote from: Stev-o on December 05, 2020, 07:18:20 AM

Rolled my K4 out of the garage yester for a "Happy Hour" cruise and when trying to start, the starter motor would not turn off even with the key or kill switch! Never had that issue before. My first thought was disconnect the battery so I opened the seat and then it stopped. I then started it up and went on my ride no further issue. Odd. Carbon buildup within the starter?

Sticking start relay, my brother had that, couldn't get it out of gear and eventually had to let go of the clutch lever. The bike ended up on it's side in the yard. Even turning off the key didn't help.

ekpent · « **Reply #22 on:** December 05, 2020, 03:00:02 PM »

I've had a solenoid stick before also. Kind of unsettling when that happens.

Stev-o · « **Reply #23 on:** December 06, 2020, 06:46:59 AM »

Quote from: ekpent on December 05, 2020, 03:00:02 PM

I've had a solenoid stick before also. Kind of unsettling when that happens.

Absolutely! I was like WTF...what can I do?!
Thanks for the info guys, I’m sure I have a replacement on the shelf.

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Author Topic: Starter Problem (Read 2429 times)