Starter Motor

[atlsec]

Hi Guys,
              Having now got to the point of starting the motor (k1) the starter ran ok on and off for about a week while testing but now runs very hot and slows down very quickly , (no plugs).There seems little resistance when turning the motor by hand so I assume the starter windings are dying . If so does anyone have a good starter to sell me? .I have looked at the ones DK are selling and they all seem to have been just hacked off the motor with no thought to the parts .I also do not think they are tested either . Please let me know asap as this is now holding up work on it . Thanks a lot , Alan .

[mike the bike]

Why not have a go at stripping it sown and servicing it.  There's only one moving part to worry about. I wouldn't mind betting the brushes are worn and the commutator needs a clean up.

[Trigger]

Hi Guys,
              Having now got to the point of starting the motor (k1) the starter ran ok on and off for about a week while testing but now runs very hot and slows down very quickly , (no plugs).There seems little resistance when turning the motor by hand so I assume the starter windings are dying . If so does anyone have a good starter to sell me? .I have looked at the ones DK are selling and they all seem to have been just hacked off the motor with no thought to the parts .I also do not think they are tested either . Please let me know asap as this is now holding up work on it . Thanks a lot , Alan .

These never go wrong. You will need:
1 tin of carb cleaner
1 tin of WD-40
Some tooth picks.
It will be down to carbon build up. Strip the motor down and clean it with carb cleaner. Use the tooth picks to scrap any carbon out of the groves. A quick look for any wear and if all looks good, a coat of WD-40 and put it back together.

 http://www.sohc.co.uk/index.php/topic,7202.msg46787.html#msg46787

[atlsec]

Hi ,
      Thanks for the replies ,I will try that this morning ,will keep you posted . Thanks , Alan .

[ginger_jim]

Wouldnt it be worthwhile replacing the bushes while you are at it.  They are really cheap anyway.

Cheers

[mike the bike]

They're called brushes not bushes.  I used to hear that all the time when I worked for Hotpoint.

[atlsec]

Hi Guys ,
              Stripped and rebuilt ,same problem .Even under no load the outer case gets very hot very quick . I suspect there is a field winding short as it registers virtually 0 ohms when measuring it .Its a pity as the rest of it looks in lovely condition .Just to let you know I am a qualified electrician so I know roughly what to look for . I could really do with trying another one just to compare the results . Thanks for all your ideas though .Cheers ,Alan 
PS , Still on the lookout for a replacement starter to buy .

[Bryanj]

I have 4 or 5 in my lockup but not sure if one is a 750 as i don't do much with those. Post a pic and i will try and compare

[ginger_jim]

Cant you get starter motors rewound? 

[AshimotoK0]

Field is virtually short circuit anyway. Best way to check is connect 12v in series with an 18 watt bulb and the field winding. The 1.5 A series current, should magnetize the pole pieces . Check that both fields have approx. same magnetism. Identify with an ohm-meter the pairs of segments on the commutator  relating to each armature coil, in turn  and pass the 1.5 A(using the bulb)  through each in turn and check for magnetism with a screwdriver on the laminations. If all OK with approximately the same magnetism, suspect the commutator is faulty or a sticking brush or brushes not contoured to the curvature of the comm. Clean up the comm as described by Trigger. If its badly scored or worn have it skimmed. The 'undercut'  of the mica between segments of the comm should be more than 0.2mm (I think but will check). As Trigger says, clean out with a toothpick and cleaner.. also Check that there is infinite resistance between the copper segments and the armature laminations and also the field coils and the tubular casing. If you can find an old motor shop with a 'growler' they can check the comm magnetics but my method above works for me.

Bet you can fix it if you do all of above or at least convince yourself that it is indeed sha**ed but as Trig says, they are normally very reliable.

The original shop manual gave very little .. My 1968 CB250/350 manual was the best on it.

Below is the '77 CB750 offering from Honda but I would still use my method in the absence of a Service tester (basically used as an Ohm-meter anyway in this test)

I do have a spare motor but I won't let it go until I have rebuilt my K0.



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Ash

[atlsec]

Hi,
     Thank you Very Much for those replies and especially the pics ,I am doing the test as Honda has shown on the field coil as we speak . Will appraise later . Thanks again , Alan .

[AshimotoK0]

Hi,
     Thank you Very Much for those replies and especially the pics ,I am doing the test as Honda has shown on the field coil as we speak . Will appraise later . Thanks again , Alan .

I know I keep banging on about it but the information is here in bucket loads in my Dropbox.... 125 meg download though so be warned 

https://www.dropbox.com/s/anpzqn2r55f1o9k/CB750%20Mega%20Parts%20Service%20and%20More.pdf?dl=0

[atlsec]

Hi Ash,
            Thanks for the drop box info ,I wish I had that before for other stuff . It seems as though the field coil is short circuit to itself and not to earth as first thought ,therefore it is not generating the correct magnetism .I will now look for a replacement .Thanks for all the help . Alan .

[Bryanj]

Resistance on field windings is very low and difficult to measure they also rarely go wrong, or to put it another way never heard of one in all the years since 75 but everything is getting older so nothing is impossible.

As said post a pic of the casing(especialy bolt orientation) and armature gear end and i will lokk in my lockup

[billy192]

I am doing up a CB 500t and the starter was not moving at all. Blowing fuses so I followed the steps on the link. The magnets (not sure what they are called) were all rusted in place. So stripped cleaned all bits light sanded the winding and the copper bit at the top. Put it back together and boom works great. The engine also was not earthen well so took off some powder coat and all works fine.

Just for info

Billy