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Author Topic: 1980 CB900F Build  (Read 4287 times)

Re: 1980 CB900F Build
« Reply #20 on: Jan 17, 2018, 00:28:38 »
Nope. Installed the battery and checked volts, 12.79V so far so good. Turned bike on to idle and it dropped to 12.38V held the revs at 3000 and it stayed on 12.38V. So no magic fix today. The reg/rec has its own earth bolt to the frame to make sure its grounded good and proper. The purple wire that shares that ground is the oil temp sender earth. I checked that its getting some AC current to it but don't know how much it should be getting so that doesn't really answer anything.
There is a pic of the earth for the crank case, big thick wire straight from the neg terminal of the battery.
Also last pic is of the earth block for all the front lights and switches. As I said, not really proud that its just tech-screwed in but its a solid earth that doesn't rely on the bearings in the head stem to be making contact.

Sooo.... why isn't it charging?
A knight in shining armour is a man who has never had his metal truly tested.

Re: 1980 CB900F Build
« Reply #21 on: Jan 17, 2018, 06:45:17 »
So I have done some reading and followed everyone's fault finding guide and I'm starting to think my Reg/Rec is not working. I pulled apart the only 3 original plugs from the wiring loom and cleaned the male and female connectors up with emery paper and pinched the female sides closed a little bit more with my long nose pliers. (pictured) After that I reassembled the plugs and was even a little bit happy with how well they clipped together, but after starting the bike and getting nothing but battery voltage out of the Reg/Rec output side i'm pretty sure that's where the problem is.
I did check the resistance of the stator slip rings and the continuity and they were all good. Seeing as its only a $25 part i'm just going to see if the one motorbike shop in this town has one in stock. (pictured)

Also I have to look into what dielectric grease is and where to get it.
A knight in shining armour is a man who has never had his metal truly tested.

Offline cxman

  • DTT SUPPORTER
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  • Posts: 2513
Re: 1980 CB900F Build
« Reply #22 on: Jan 17, 2018, 07:42:40 »
check the resistance on the charging rotor

and inspect the brushes if they do not have good continuity thet reg cant energize the rotor

make sure they meat left and are not sitting at the replace mark

what was the resistance of the rotor?

if you are stuck i probably have a few airboxes from where i swapped carbs on mine
« Last Edit: Jan 17, 2018, 07:45:15 by cxman »
1978 CX650 Super Deluxe
1979 XS1100 Special
1974 xl350
1983 cx650 Custom
1973 cb750
1980 cb750
1981 cb650
1982 cb900 c
1974 kawasaki 350 bighorn
1983 GL1100 aspy full dress
1983 GL1100 Nekid
and a bunch of others

Offline crazypj

  • Posts: 13178
  • Split personality, I fake being smart
Re: 1980 CB900F Build
« Reply #23 on: Jan 17, 2018, 09:55:42 »
It's a long time since I worked on 750/900 (mid 1980's) Pretty sure the earth is under one of the rear case bolts then onto frame either on a tapped hole in lower rear engine plate or under a bolt head? ( I would have to dig out a manual to check)
Generator rotor could be suspect, they are very reliable but don't like being smacked about (do any of us?  ;D )
 I only read about the cover damage this morning (it's 8.54am in Florida)
Did you get correct instructions with battery? Let it stand a minimum of 1 hr but preferably 24 hrs, check voltage  and charge at 1/10 of capacity for 12 hrs or max charge rate printed on it somewhere for 1~3 hrs (may be on instruction sheet.
SLA has a slightly 'more acidic' acid than conventional 'wet cell' ( from memory I think 1.32sg instead of 1.26~1.27sg)
« Last Edit: Jan 17, 2018, 10:02:26 by crazypj »
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline jetmechmarty

  • Posts: 343
Re: 1980 CB900F Build
« Reply #24 on: Jan 17, 2018, 10:47:14 »
Also I have to look into what dielectric grease is and where to get it.

Dielectric grease is an insulator.  It can not make your connections better.  It can make them worse.  I know there is controversy over the stuff.  It's good for lubing o'rings, otherwise, I have little use for it.
Marty (in Georgia)
XS650

Offline jetmechmarty

  • Posts: 343
Re: 1980 CB900F Build
« Reply #25 on: Jan 17, 2018, 10:56:53 »
CXMAN asked the resistance of the rotor.  Good question.  It should be about five ohms.  You'll have no field if it's shorted, just a dead battery.  I'm not familiar with your Honda, but from my chair I'd ask if a shorted rotor could damage the regulator.  Measure slip ring to slip ring. 
Marty (in Georgia)
XS650

Offline crazypj

  • Posts: 13178
  • Split personality, I fake being smart
Re: 1980 CB900F Build
« Reply #26 on: Jan 17, 2018, 11:25:51 »
It's an EMF system, so shorted rotor could damage reg/rect as it will try  to power field coi,l not get  expected~14v so allow full battery voltage. As it's voltage regulated not current regulated it shouldn't be possible to overheat windings with a dying battery. If you connected a car battery  up with engine running, that could easily supply enough amps @ around 15v to fry things.
I'm guessing $25.00 is price of used part?
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline jetmechmarty

  • Posts: 343
Re: 1980 CB900F Build
« Reply #27 on: Jan 17, 2018, 15:36:11 »
If the rotor is bad, the best option is

Custom Rewind
2014 Pratt Hwy, Birmingham, AL 35214
205-798-7282
Marty (in Georgia)
XS650

Re: 1980 CB900F Build
« Reply #28 on: Jan 17, 2018, 19:13:32 »
Thanks for the help fella's, to answer a few questions the brushes have a fair bit of meat left on them as seen in the pic and there is no resistance between them and the bolts holding them in. I know the pic I put up here says 4 Ohms but thats because I was holding it in one hand to take a pic and couldn't get a great connection, but with two hands it was definitely 0.
The resistance between the slip rings on the generator rotor is 4.3 Ohms and from memory that within range?
Also resistance between the stator coils is 0.4 Ohms which is inside the allowable 0.4 to 0.5 range. and I checked all 3 yellow coil  wires not just the one pictured.

Who would have known this would be so much fun!
A knight in shining armour is a man who has never had his metal truly tested.

Re: 1980 CB900F Build
« Reply #29 on: Jan 17, 2018, 19:17:55 »
It's a long time since I worked on 750/900 (mid 1980's) Pretty sure the earth is under one of the rear case bolts then onto frame either on a tapped hole in lower rear engine plate or under a bolt head? ( I would have to dig out a manual to check)
Generator rotor could be suspect, they are very reliable but don't like being smacked about (do any of us?  ;D )
 I only read about the cover damage this morning (it's 8.54am in Florida)
Did you get correct instructions with battery? Let it stand a minimum of 1 hr but preferably 24 hrs, check voltage  and charge at 1/10 of capacity for 12 hrs or max charge rate printed on it somewhere for 1~3 hrs (may be on instruction sheet.
SLA has a slightly 'more acidic' acid than conventional 'wet cell' ( from memory I think 1.32sg instead of 1.26~1.27sg)

Instruction with the battery were "The instructions are inside" I read it and it said it only needs 20 mins for the electrolyte to flow in then its good to go. I did think there was more to it than that. Now I know for next time.
A knight in shining armour is a man who has never had his metal truly tested.