Author Topic: CB900c starter won't spin and oil pressure wire is cut (Read 9492 times)

Hondawggie · « **on:** January 15, 2012, 05:10:46 PM »

Hi folks -- I just found a neglected 1981 CB900c and I have her ready to go with flushed gas tank, new inline gas, filter, plugs, oil, carbs ready, battery at full charge -- I put the key in the ignition and all dashboard indicators work, horn works, etc.

When I pull in the clutch and press the starter button with the off-run-off switch in the 'on' position the starter motor does not spin. Just to make sure I put my motorcycle/snowmobile portable jump starter on and no change. The starter motor won't turn.

So I got to looking around the starter motor area just below the carbs.

There is a wire on the right side of the starter motor cover, just a single wire, and it's broken -- I believe it originally was connected to a round cap of some sort on top of the crankcase immediately behind the cylinder in the middle top of the crankcase, to the right of the starter motor cover.

I believe this round 'cap' might be the neutral switch or the oil pressure switch.

Would this broken wire explain why the starter won't turn over?

grcamna2 · « **Reply #1 on:** January 15, 2012, 05:43:51 PM »

Hondawggie,
What will it do if you try jumping the starter across the solenoid directly w/ a large flat screwdriver ?

City Boy · « **Reply #2 on:** January 15, 2012, 06:03:27 PM »

Hi.First up,the broken wire goes where you figured and that is the oil pressure switch .Easy to hook back up.I have some experience with this engine family and I would say the starter electrical system is pretty solid IF it has not been buggered with.Like grcamna2 says,look to the solenoid under the left side cover first.If the bike has sat awhile it may be just stuck.Try a few light taps on the sol.magnet as you engage the starter.If that fails, like said before,jump the solenoid and then go from there. Good luck and Rock On

Hondawggie · « **Reply #3 on:** January 15, 2012, 06:05:44 PM »

Quote from: grcamna2 on January 15, 2012, 05:43:51 PM

Hondawggie,
What will it do if you try jumping the starter across the solenoid directly w/ a large flat screwdriver ?

Not sure but I suspect the screwdriver blade will get mighty hot. Before I take such a measure -- do you know if that broken wire when re-connected will fix it? There is a single wire coming out next to the right side of the starter motor cover that connects up to either a neutral switch or oil pressure switch, not sure what kind of switch it is.

Hondawggie · « **Reply #4 on:** January 15, 2012, 06:08:22 PM »

Quote from: City Boy on January 15, 2012, 06:03:27 PM

Hi.First up,the broken wire goes where you figured and that is the oil pressure switch .Easy to hook back up.I have some experience with this engine family and I would say the starter electrical system is pretty solid IF it has not been buggered with.Like grcamna2 says,look to the solenoid under the left side cover first.If the bike has sat awhile it may be just stuck.Try a few light taps on the sol.magnet as you engage the starter.If that fails, like said before,jump the solenoid and then go from there. Good luck and Rock On

I will be tapping on that guy tomorrow then thanks to both of you. Correct me if I'm wrong but a disconnected oil pressure switch plays no role in whether the starter motor will turn.

w1sa · « **Reply #5 on:** January 15, 2012, 06:25:22 PM »

The 'oil pressure switch' wire serves as a ground connection (thru the pressure switch), only. ........it is not part of the starter relay/switch circuit.

Hondawggie · « **Reply #6 on:** January 15, 2012, 06:37:22 PM »

Quote from: w1sa on January 15, 2012, 06:25:22 PM

The 'oil pressure switch' wire serves as a ground connection (thru the pressure switch), only. ........it is not part of the starter relay/switch circuit.

That does me. I have thus eliminated that broken wire as the cause of 'starter won't spin.'

So I guess with all the other electrics working -- I will look at the following tomorrow, let me know if I'm on track and/or left something out that could be checked. By the way the bike sat outside for 2 years but very little rust so must've had a tarp on it. The guy put it away dry -- empty gas tank and empty carbs (yay). Gas tank has very minimal inside oxidation, 90+% of bare metal is clean in there.

Here's what I'll check, keeping in mind the dashboard lights (neutral, turn signals, beam, horn) all work fine:

1) switch at clutch lever -- there are 2 blade-style contacts at the clutch lever so I assume there's a lock-out switch in the lever area so the starter won't spin unless the clutch's pulled in, I'll use my ohmmeter to see if the clutch-is-closed-now switch works

2) starter button -- probably check for 12 volts into the switch then 0-or-12 volts on the output side of the starter button as I push and release the switch

3) check for 0-or-12-volts on side of the starter relay not connected to the battery -- I noticed one side is connected to the battery and the other side of the relay I believe needs to show 12 volts when I push the starter button

Then if that's all fine, next I'll find the ground for the starter motor and see if it's good.

If that's all good I'm pulling the starter motor out to bench test it and maybe replace it.

Sound right? Have I missed anything?

w1sa · « **Reply #7 on:** January 15, 2012, 07:46:47 PM »

You shouldn't need to pull the clutch lever to activate the starter, unless the bike is in gear or the neutral switch/diode are malfunctioning/disconnected......

Hondawggie · « **Reply #8 on:** January 15, 2012, 08:30:54 PM »

Quote from: w1sa on January 15, 2012, 07:46:47 PM

You shouldn't need to pull the clutch lever to activate the starter, unless the bike is in gear or the neutral switch/diode are malfunctioning/disconnected......

There's something electrical though going on with the clutch lever being pulled-in/released -- there at 2 wires leading to 2 blade-type connectors on the lever's perch, right behind the cable. Not sure why any other part of the bike would need to know if the clutch is pulled in besides the starter motor.

Brings up a bad memory. I had a '72 cb750 with a near-perfect gas tank on the side stand. An acquaintance was over that day. When the starter button was pushed the bike being in gear leapt forward, right off the side stand, now the '72 near-perfect tank is dented and the bike is down on the left side.

Of all the gott-dang shimmy-doo-hah you do not want a moron around your nice '72, they did not have a starter lockout for the clutch lever.

w1sa · « **Reply #9 on:** January 15, 2012, 09:14:31 PM »

Yea, you are spot on, especially with earlier models.......I didn't mean you shouldn't pull the clutch lever to activate the starter, it is an extra safety feature we should all use more often.........I simply meant, you can physically activate the starter, without pulling the clutch lever, so long as the neutral switch is activated and functioning correctly........each of the neutral switch and clutch lever switch provide and share a ground path, allowing the starter circuit to function properly....

Hondawggie · « **Reply #10 on:** January 15, 2012, 09:54:18 PM »

Quote from: w1sa on January 15, 2012, 09:14:31 PM

Yea, you are spot on, especially with earlier models.......I didn't mean you shouldn't pull the clutch lever to activate the starter, it is an extra safety feature we should all use more often.........I simply meant, you can physically activate the starter, without pulling the clutch lever, so long as the neutral switch is activated and functioning correctly........each of the neutral switch and clutch lever switch provide and share a ground path, allowing the starter circuit to function properly....

You sound knowledgeable on this and it is appreciated -- sounds like as long as the neutral light comes on the starter should spin and the neutral light was in fact coming on today when I tried to start her.

That pretty much eliminates a lot of that checking of switches I was going to do, except maybe the actual start button itself.

Sounds like I need to check for 0v-then-12volts on the non-battery side of the starter relay as I push and release the start button.

I will first give the relay a tap with a large screwdriver handle before checking it. If I see 12v-then-0v on the starter side of the relay as I push-then-release the starter button -- either the ground for the starter is not making contact or the starter is froze up which would surprise me as the cb900c only has 10,000 miles on her and I've never heard of or seen a Honda starter motor go bad on that low miles. First time for everything though I reckon.

Come to think of it -- I just realized something. Today when I was pushing the starter button, I did not even hear the relay clicking open/close. That tells me it's either the start button or the relay is stuck.

I'm itching to check these 2 things as I feel a lot closer to solving the real problem which apparently has nothing to do with my opening surmise in this thread, what turned out to be a side issue the oil pressure switch, I'll get to that later tomorrow. First I want to start this beast after 3 years of setting.

I did spray some Amazing PB Blaster in the cylinders and put it in 5th gear with the spark plugs out and rotated the back wheel to lube up the cylinder walls, seems like she's turning over fine.

w1sa · « **Reply #11 on:** January 15, 2012, 10:22:57 PM »

Yea....I would check the connectivity/continuities between the battery/switched power from the ignition switch to the starter switch and then to the starter relay switch....s/b red to black at ign sw, black to red/yellow at starter sw, red yellow at starter relay............proper connectivity should allow voltage to the end of that red/yellow wire at the starter relay end.....
If the neutral switch activation/ground is not connecting thru the diode to the starter relay and, the clutch switch ground path is also interrupted/faulty, you still wont get the starter to operate normally via the starter switch....(less likely problem, but not impossible)

Hondawggie · « **Reply #12 on:** January 15, 2012, 10:28:07 PM »

Quote from: w1sa on January 15, 2012, 10:22:57 PM

Yea....I would check the connectivity/continuities between the battery/switched power from the ignition switch to the starter switch and then to the starter relay switch....s/b red to black at ign sw, black to red/yellow at starter sw, red yellow at starter relay............proper connectivity should allow voltage to the end of that red/yellow wire at the starter relay end.....
If the neutral switch activation/ground is not connecting thru the diode to the starter relay and, the clutch switch ground path is also interrupted/faulty, you still wont get the starter to operate normally via the starter switch....(less likely problem, but not impossible)

Okay sounds like a good plan of things to check -- hopefully tomorrow I'll find the issue and report back that the bike runs after 3 years of being neglected.

Hondawggie · « **Reply #13 on:** January 16, 2012, 06:34:29 PM »

Here's the update after I checked my '81 cb900c today.

Yesterday I was not hearing any clicking from the starter relay that I thought I *should* hear if the starter relay was working.

So I disconnected and removed the relay and had a look at it. There was rust on the top of it, the relay is a metal can sort of, with two screws sticking upward on its top -- one of the screws is the contact for the battery.

The other screw on the top of the starter relay is a contact that connects to the starter motor -- I will call that the 'output side' of the starter relay.

The rust on the top of the starter relay can was not on the 2 screw contacts, only on the top of the can. So I wire-brushed the top of the starter relay. Then being a hillbilly fumble fingers type of individual I dropped the dang starter relay onto the concrete. "Oh well that oughtta knock its innards loose."

I put the relay back in and turned on the key and pushed the starter button -- BAM I heard that start relay clicking away like a deuce.

I heard the relay click open then close -- it was loud -- I guess that drop taught it who's the boss. It was making a loud click, more like a clunk as I pushed and released the starter button on the handlebar.

Then I heard the starter motor spin -- but only for a few seconds. Then back to the clicking relay.

I put my volt meter on the output side of the starter relay. I wanted to see the output go from zero to 12volts when I pushed the start button.

I pushed the start button and hear the relay click open -- but the output side of the starter relay is zero volts, it never jumps up to 12volts.

I did *not* disconnect the wire on the starter relay that leads to the start motor -- so in theory, the reason I am not seeing 12 volts on the output of the relay is -- the output is shorted to ground. But if that were true the 30amp main fuse would blow and that isn't happening, the power stays on -- lights, horn, etc.

So it looks like, while the drop to the ground loosened up the innards of the starter relay (yesterday the starter relay was not clicking at all) -- so in theory the relay is working -- I'm not seeing 12 volts on the output of the relay even though I can *hear* and even feel the relay's inside parts moving when I push the starter button.

So any suggestion here are appreaciated - I've never done troubleshooting on the starter circuit on a bike before today.

w1sa · « **Reply #14 on:** January 17, 2012, 04:34:03 AM »

Yes, you should see good voltage (11 volts + with good battery) on the starter motor side (heavy black wire/cable) post of the relay switch..........if your relay/solenoid is now working, it should close the contacts and allow the battery voltage to bridge directly to the starter motor wire.............solenoid clicking (without starting) is usually caused by poor/flat battery and or loose/corroded connections in the circuit/relay...........it seems what you describe could be like that............undo and clean the black wire connection, replace and retry. If that fails I would check the condition of the relay inner contacts for pitting and corrosion.

The previously mentioned method of bridging the two posts with a heavy screwdriver (or similar) is the other (quicker) way of confirming the relay/solenoid as faulty, before teardown/replacement.

Hondawggie · « **Reply #15 on:** January 17, 2012, 07:15:21 AM »

Quote from: w1sa on January 17, 2012, 04:34:03 AM

Yes, you should see good voltage (11 volts + with good battery) on the starter motor side (heavy black wire/cable) post of the relay switch..........if your relay/solenoid is now working, it should close the contacts and allow the battery voltage to bridge directly to the starter motor wire.............solenoid clicking (without starting) is usually caused by poor/flat battery and or loose/corroded connections in the circuit/relay...........it seems what you describe could be like that............undo and clean the black wire connection, replace and retry. If that fails I would check the condition of the relay inner contacts for pitting and corrosion.

The previously mentioned method of bridging the two posts with a heavy screwdriver (or similar) is the other (quicker) way of confirming the relay/solenoid as faulty, before teardown/replacement.

I accidentally bridged the 2 poles atop the starter relay yesterday. That led to the starter motor spinning round. So it was then I knew the starter motor was okay. And after that was when I removed, wire-brushed and dropped the relay which led to hearing internal clicking in the relay after I reinstalled it and pushed the start button.

So my idea is this -- the rust on top of the starter relay means water sat there a long time and may have fallen into the innards of the starter relay -- and even though the relay inside is moving on/off correctly -- it has rust inside which is stopping the 12volts from getting through despite the internal contact being made.

Can the starter relay be taken apart? I'd like to open her up and clean off the inside contacts. I can hear the contact bar inside of it moving -- there is just rust in there not making a good electrical connection.

Or is the starter relay not able to be taken apart for cleaning?

This same starter relay is used on all Honda street bikes from 1979 to about 1985 -- the CBX, cb1100f, Goldwing, gl500, cb550, cb650, cb750, Nighthawk 700, all Honda streetbikes from that time.

w1sa · « **Reply #16 on:** January 17, 2012, 03:16:44 PM »

I haven't had to open mine........there is probably a couple of screws on the top of the relay where the main voltage posts are........if you've checked and cleaned all connections, and verified the starter spins well when by-passing the switch, there is probably nothing to lose by attempting to open and check it inside.......

Hondawggie · « **Reply #17 on:** January 17, 2012, 05:23:07 PM »

Quote from: w1sa on January 17, 2012, 03:16:44 PM

I haven't had to open mine........there is probably a couple of screws on the top of the relay where the main voltage posts are........if you've checked and cleaned all connections, and verified the starter spins well when by-passing the switch, there is probably nothing to lose by attempting to open and check it inside.......

Okay tomorrow I'm going to go mad scientist and see if I can open it up without damaging it -- they are available still but not cheap. If I'm successful I'll post pictures back of the innards. If I can't get it open I'll have to buy a NOS one.

w1sa · « **Reply #18 on:** January 17, 2012, 05:27:28 PM »

.........way to go......post some pics and comments as you proceed and show what you find....good luck

Danno · « **Reply #19 on:** January 18, 2012, 12:15:05 AM »

I believe that model of bike has safety diodes and if they are blown that could be your problem some can be unplugged others must be replaced and some can just be turned around and plugged in backwards take a look at your wiring schematic and consult a good repair manual this is a big problem on my gl 1000's but on them all I have to do is unplug them

Hondawggie · « **Reply #20 on:** January 18, 2012, 06:37:39 AM »

Quote from: Danno on January 18, 2012, 12:15:05 AM

I believe that model of bike has safety diodes and if they are blown that could be your problem some can be unplugged others must be replaced and some can just be turned around and plugged in backwards take a look at your wiring schematic and consult a good repair manual this is a big problem on my gl 1000's but on them all I have to do is unplug them

I have got hold of a manual and found a diode in the starter motor circuit shown here:

I'm not quite sure as to *where* this one diode is though -- I can see it in the diagram but the physical location of it on the bike, I'm not sure of. I'm going to pull the starter relay and attempt disassembly in a few hours after the sun comes up.

If you look at the innards of the 'STARTER RELAY SWITCH' in the diagram, you will notice a big 'T'-shaped piece that I believe has the rust on it. When the 'RELAY COIL' in the diagram is activated, my guess from looking at the picture is -- that big 'T'-shaped piece rises upward and connects the battery-side contact on the starter relay -- to the other contact which is wired up to the starter motor.

So I'm guessing that if I can get her opened up, I will find rust on the top of that big 'T' there.

Hondawggie · « **Reply #21 on:** January 18, 2012, 10:33:30 AM »

I got the starter relay out and getting ready for disassembly/refurbishment.

I put my best dog on it.

Hondawggie · « **Reply #22 on:** January 18, 2012, 01:12:07 PM »

So I asked the dog "Looks simple enough to me, think you can get this apart? How hard could it be?"

Well she came back with "Ruff. Ruff, ruff, ruff."

I trusted her anyway and let her go to work, big mistake,
she let me down, broke 2 thin wires on it. Bad dog.

Did the water that rusted the top of the relay get inside it yes it did.

Remove screws and the 2 nuts on the top.

Oxidation on the 2 screw poles prevented electrical contact. Hosed.
Gott dang Dobermans keep them clear of small parts, their paws are too big.

She feels bad about it I can tell, she offered her next 3 treats up so I can afford a new
starter relay. I let her chew on things for a while.

Ebay here we go.

w1sa · « **Reply #23 on:** January 18, 2012, 01:45:30 PM »

Hopefully, that's the extent of your problem......bummer...........I've seen solenoids resurrected by cleaning away serious rust/oxidation like that. I've done it myself with horns and such, but with the broken wires, yours is probably well and truly toast. Thanks for the visuals.......good luck with the rest of the project

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Author Topic: CB900c starter won't spin and oil pressure wire is cut (Read 9492 times)