Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: atlsec on June 20, 2015, 08:13:15 PM
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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 .
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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.
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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
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Hi ,
Thanks for the replies ,I will try that this morning ,will keep you posted . Thanks , Alan .
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Wouldnt it be worthwhile replacing the bushes while you are at it. They are really cheap anyway.
Cheers
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They're called brushes not bushes. I used to hear that all the time when I worked for Hotpoint.
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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 .
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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
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Cant you get starter motors rewound?
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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.
[attachimg=1][attachimg=2][attachimg=3]
Ash
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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 .
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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 ;D
https://www.dropbox.com/s/anpzqn2r55f1o9k/CB750%20Mega%20Parts%20Service%20and%20More.pdf?dl=0
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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 .
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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
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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
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Hi Guys,
Thank you for all your help . Have you ever been as red faced as I am now !!!!!!!!!!!! ,a bloody flat battery and an iffy solenoid caused these problems . Two sodding wasted days of work and a lot of your valuable time wasted as well .I do apologise for my stupidity . It goes to show that you must always look for the simple things first .I am going to lie down now ,I may be some time . Cheers ,Alan the stupid .
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Don't worry about it, we all do it.
You need the Ashimoto patented low voltage protection device. B8stards I worked for let the patent lapse so you can copy it. :D
http://www.google.co.uk/patents/US5604656
[attachimg=1]
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The effort wasn't entirely wasted, at least you've checked and serviced the starter - most people don't bother with it.
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Thanks Mike,
At least that makes me feel a bit better ,your right to say that some things just get left because they still work but I can tell you I have the cleanest innards of any starter motor bar none now . Just to let you all know that I have just ordered all my new bodywork from Yamiya .I will let you know how good etc , Also I have used Marcel in Holland to do my dials .I sent them to him Parcelforce and they were smashed on arrival (more expense) so be warned and pack them well .
That's all for now ,Cheers ,Alan .
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Ash.... you never cease to amaze. You're on the wrong forum....... or is is this just forum #74 of many, with a 'Master Builder' moniker on NASA somewhere in the top 5?
In awe as always.
Atlsec... great! At least you don't take it all too seriously to own up! Made me laugh, only because I've been there (too many times) myself!
Simon
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Hi Simon ,
I was also having a laugh at my own expense until the starter played up again !!!!.This time making a horrible whining noise and going slow .After a strip down again I noticed a wear mark on the armature as if rubbing on something ?. It turned to be an exceedingly worn end bush which you cannot spot when re-assembling allowing the armature to move laterally in the housing .Bought a replacement starter and all is well again . New bodywork here and is amazing quality (gold) .Also fitted new exhaust system ,not too difficult and looks gorgeous .I think when this bike is done I will put it on a pedestal and just look at it . Got the clocks back from Marcel ,he really knows his stuff and they also look new as well . Just waiting for my seat and shocks to arrive from the States and for Steve at Wheelwise to do his bit and we are almost done .Thanks for all your help in doing this ,Cheers , Alan .
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Sounds like no expense has been spared.... can't wait to see the pics.
Pedestal in the living room sounds ideal.... certainly way better to look at than the bloody telly.
I too used Marcel for my CB750 faces... what a great service. I may (ultimately) export my bike to Oz; he sent me a free KPH face FOC. Fantastic service.
Cheers again, and glad you've fully fettled that starter...
Simon.
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Hi Simon ,
Your right about the astronomic cost of doing the bike right . What amazes me though is the amount of bikes I see for sale as supposedly correct but even a newbie like me can spot the errors . It always seems to be the same things that people get wrong namely the seat the shocks or the exhaust .As mine is a K1 I have had the extra expense of the K0 shocks and exhaust which is much more expensive than a K2 .I fitted these parts so if anyone looks at it I do not want the embarrassment of these things being pointed out to me . That does not mean I have got every thing right though . I am sure when I post the pics someone will tell me otherwise ,I hope . Cheers Alan .
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Nice to have the bike spot on, but when it costs more than the bike is worth is it really necessary? I was outside my local Honda dealership with my restored 750F2 with the aftermarket exhaust (Motad), and the so called classic expert that works there asked me why I didn't have the standard 4 into 2 exhaust fitted. Glad I didn't go to the ridiculous expense of a NOS 4 into 1 now (that's if I could even find one). Very few people will spot the errors, and who cares anyway if its a superb looking bike. Just my opinion, hope I don't upset anyone. :D
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