ST90 (New Build) Electrical & Engine Problems - HELP PLEASE :-)

Discussion in 'CT90, CT110, ST70, ST90 Discussion' started by DAX-IT!!!, Mar 21, 2021.

  1. DAX-IT!!!

    DAX-IT!!! Member

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    Hi Guys
    Haven't posted for a while as I've been rebuilding the bike - its pretty much rebuilt now. The bike now starts/runs etc but here are a couple of my problems.

    Firstly, electrical. Can anybody tell me (in childlike terms as I am a complete THICKO when it comes to electrical issues and following instructions regarding electrics - assume I know NOTHING about testing items etc) how to test the OEM factory fitted rectifier that's on my ST90? I've looked on the net but its all about 12v rectifiers that are not similar to the one fitted on the ST90. Please guys tell me about the one fitted to the ST90, not one similar to it.

    Secondly, how can I test whether or not the alternator (submerged in the engine oil) in the engine is functioning correctly ??

    My reason for asking is that I think my battery is OK, (it was new 3yrs ago and has been kept on an optimate ever since) but I dont think its being charged properly whilst the bike is running. Lights are bright but dont appear to get brighter when revving the engine and neither do the indicators (they dont flash very fast either).

    Here's how I tested the electrical charging:-

    Battery connected to bike, I'm getting just over 6.35v.

    Switch on, bike NOT running, only neutral light on 6.05v.

    Start bike from cold, leave ticking over 6.7/8v.

    Leave ticking over, put h/lights on 6.1v.

    Leave ticking over, put lights and indicators on 5.8v.

    Then rev bike to a constant 3 to 4000rpm with lights & indicators on 5.8v.

    Then bike back to ticking over, 6.4v.

    My other issue is when bike is warm and I switch off, it sounds like something is still spinning round in the engine for a few seconds even though the engine has completely stopped. It sounds a little bit like a ratchet (like kickstart). :unsure: The kickstart works fine. Your advice/input appreciated :) (y)
     
    #1 DAX-IT!!!, Mar 21, 2021
    Last edited: Mar 22, 2021
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  3. lukelaw1

    lukelaw1 Active Member

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    ok here we go, btw i am no expert.

    long story short
    the rectifier converts the ac voltage to dc voltage.
    the end!


    The rectifier consists of diodes. in this example there are 4 diodes, i know this by looking at the st90 wiring diagram. a diode only allow electricity "current" to flow in one direction. "A ONE WAY STREET" we will use this later on.

    With the rectifier unhooked and removed from the bike it time to test.

    set your digital multi meter to ohms

    make sure you set the rectifier on a non conductive table. do this to prevent a false reading.


    disclaimer im not a professional
    when you do this testing do not pinch the end of the volt meter lead to the end of the wire with your fingers. the meter will read continuity through you skin.


    1st test:
    red test lead=green wire
    black lead=yellow wire
    record results

    red test lead=green wire
    black lead=pink wire
    record results

    red test lead=green wire
    black lead=red/white wire
    record results

    2nd test is the same as 1st test just interchange the red and black leads on the meter. and record results. i dont remember for sure but i think all of test results from test 1 will be OL. and test 2 results will have low resistance readings.

    if you have low resistance readings on both tests the rectifier is bad.
    if test results seem to be in line with above continue with test 3.

    test3
    red test lead=pink wire
    black lead=red/white wire
    record results
    (interchange red and black leads and record result again) one combination should give you OL ohms and the other should read low resistance.

    Test4
    red test lead=yellow wire
    black lead=red/white wire
    record results
    (interchange red and black leads and record result again) one combination should give you OL ohms and the other should read low resistance.


    this should test every combination of wires and current flow directions. if one of the diodes is bad you wont get the charge at the battery.
     
  4. lukelaw1

    lukelaw1 Active Member

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    st90 wiring.jpg here is the wiring diagram
     
  5. OLD CT

    OLD CT Well-Known Member

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    I am no expert but it sounds like the 3 year old battery IS to blame and it's failing the ''load test''...
     
  6. b52bombardier1

    b52bombardier1 Well-Known Member

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    Yes, a three year old battery is likely deader than Millard Fillmore. An operational test for the rectifier is done with a multimeter set to AC volts at the battery. Hope to see very, very low amounts of diode leakage there at way less than .1 volts AC (less than a tenth of one volt) with the engine running. Even revved up to half throttle, expect to see it still below a tenth of a volt.

    Much more means one or more bad diodes in the rectifier.

    Rick
     
  7. DAX-IT!!!

    DAX-IT!!! Member

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    OK guys, sorry for not getting back sooner; I've been a bit tied up with stuff. Firstly, thanks so far to luke law1 for his reply - I'll get the rectifier off the bike and see if I can do those tests. Secondly, thanks to the other replies aswell.

    Rick, (b52bombardier) if I understood only one part of your reply it would be the part where you said "An operational test for the rectifier is done with a multimeter set to AC volts at the battery." I guess that means turn the dial on the multimeter to AC volts and connect it to the battery whilst its in situ on the bike but, after that, everything you said about seeing very, very low amounts of diode leakage there at way less than .1 volts AC (less than a tenth of one volt) with the engine running is Gobbledy Gook to me - I simply dont understand what you mean or know how to interprete what is being displayed on the multi-meter - sorry :confused:

    I'm aftraid when it comes to electrics and reading digital meters on settings other than volts - I'm a total plonker !!!! :confused: I have borrowed a multi-meter off a friend of mine - here's a picture of it

    P1110073.JPG

    I think its a decent meter so hopefully should be fine. I'll put the results of the test on the rectifier up shortly. If anyone can tell me if theres a position on the dial (other than the DC volts and AC volts) that could be of use to me (and how to read and interpret the readings on the display) that would be helpful :)

    Also, has anyone got any info on how to test the alternator (submerged in the engine oil) whilst its still in situ on the bike?


    Lastly, anyone got any ideas on that noise from my engine that I described previously :confused:
     
    #6 DAX-IT!!!, Mar 23, 2021
    Last edited: Mar 23, 2021
  8. b52bombardier1

    b52bombardier1 Well-Known Member

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    That noise after the engine quits is the clutch spinning to a stop. Nothing to worry about as long as its shifting nicely.

    Rick
     
  9. DAX-IT!!!

    DAX-IT!!! Member

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    I hope you're right :) Thanks Rick (y)
     
  10. lukelaw1

    lukelaw1 Active Member

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    You have a pretty good Digital multi meter. Going clock wise from the off position is

    AC voltage
    DC voltage
    ohms with beeper
    ohms
    diode tester
    capacitor tester
     

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