CB900C oil light
07-23-2015, 09:00 PM
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CB900C oil light
Hi all, I'm somewhat new to the motorcycle game and I've been fixing up my 1980 CB900C over the last few months. I'm trying to sort out all of the problems that have crept up on this 35 year old motorcycle 
I recently noticed an issue with the oil light when I began to ride at night, it comes on when I depress the clutch. The light flickers as if the oil level is low but it only happens when I'm using the clutch, at speed or sitting at idle. The light doesn't come on during hard acceleration, going up or down hill, etc. Only flickers when the clutch is in and the engine is warmed up. Very odd and slightly annoying!
I'm pretty **** about checking the oil level, and I use the correct Honda procedure of putting the bike on the center stand, letting it idle for a few minutes, and then checking the oil level after letting it settle. As for the oil itself, I'm using Rotella 15w40. Here's what I've done so far:
* Replaced the oil light sensor on the engine
* Replaced the fraying connector on the wiring harness
* Verified that the wiring from the light to the headlight bucket is good along with the ground
* Disconnected the clutch switch by the lever (anyone know exactly what this does, btw?)
* Adjusted the barrel adjuster on the clutch lever to see if it had something do with the clutch being engaged
* I should also note that I've removed the oil pump cover in order to replace the shifter shaft seal. I RTV'd it back into place and it hasn't leaked since.
Does anyone have any suggestions? I don't want to ride if I'm risking damage to my bike, but it only seems to be an issue if I'm using the clutch. I'm thinking that maybe the oil pump is slightly weak, or it may have something to do with the clutch discs wearing down? Maybe excessive space between the plates causing the oil to disperse into those empty spaces, thus lowering pressure?
I think I might pull the oil pan and see if the strainer is clogged. The gasket needs to be replaced anyways and I've got one coming. I also have another oil pump I can try out from my spare engine but I don't know its condition. I'll also need to order a gasket from eBay since Honda doesn't seem to stock them anymore if decide to pull it.
TIA!
I recently noticed an issue with the oil light when I began to ride at night, it comes on when I depress the clutch. The light flickers as if the oil level is low but it only happens when I'm using the clutch, at speed or sitting at idle. The light doesn't come on during hard acceleration, going up or down hill, etc. Only flickers when the clutch is in and the engine is warmed up. Very odd and slightly annoying!I'm pretty **** about checking the oil level, and I use the correct Honda procedure of putting the bike on the center stand, letting it idle for a few minutes, and then checking the oil level after letting it settle. As for the oil itself, I'm using Rotella 15w40. Here's what I've done so far:
* Replaced the oil light sensor on the engine
* Replaced the fraying connector on the wiring harness
* Verified that the wiring from the light to the headlight bucket is good along with the ground
* Disconnected the clutch switch by the lever (anyone know exactly what this does, btw?)
* Adjusted the barrel adjuster on the clutch lever to see if it had something do with the clutch being engaged
* I should also note that I've removed the oil pump cover in order to replace the shifter shaft seal. I RTV'd it back into place and it hasn't leaked since.
Does anyone have any suggestions? I don't want to ride if I'm risking damage to my bike, but it only seems to be an issue if I'm using the clutch. I'm thinking that maybe the oil pump is slightly weak, or it may have something to do with the clutch discs wearing down? Maybe excessive space between the plates causing the oil to disperse into those empty spaces, thus lowering pressure?
I think I might pull the oil pan and see if the strainer is clogged. The gasket needs to be replaced anyways and I've got one coming. I also have another oil pump I can try out from my spare engine but I don't know its condition. I'll also need to order a gasket from eBay since Honda doesn't seem to stock them anymore if decide to pull it.
TIA!
08-01-2015, 05:29 PM
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Re: CB900C oil light
I'm pretty sure your bike has an oil pressure switch, and if the idle is too low, it will cause the light to flicker. Try bumping the idle up a few hundred RPM. Also, like you mentioned, a clogged pump strainer can cause this issue, as well as a bad/clogged filter. The pumps don't wear out really, unless the engine had a bearing go bad at some point, or some other catastrophic failure and the pump sucked up some junk and scored the walls, causing the clearance to bee really loose. You would still have enough volume from the pump, but not the pressure. Or course, there is always the chance that it is an electrical issue, possibly a ground issue. I believe the light always has 12v on it, and when the switch closes, it completes the circuit, turning the light on.
Edit: The clutch switch is there to allow you to start the bike while it is still in gear, but only when the clutch is pulled in. This is a safety feature, so you don't hit the starter button by accident and have the bike lurch forward, causing you maybe drop it.
Edit: The clutch switch is there to allow you to start the bike while it is still in gear, but only when the clutch is pulled in. This is a safety feature, so you don't hit the starter button by accident and have the bike lurch forward, causing you maybe drop it.
08-06-2015, 04:02 PM
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Re: CB900C oil light
Thanks for your input. The idle is actually a bit high at the moment, around 1500 RPM. I pulled the pan off and removed the strainer, and sure enough, it was pretty clogged up with some metal and debris. It's probably never been cleaned!
It's too bad though, I thought this would solve my problems but when I ran the bike for 20-30 minutes the issue came back. I'm thinking that when the oil heats up it becomes a bit too thin and the light is triggered. Again, this mostly happens when I hold in the clutch so doing that must change the way the oil is circulating internally. Maybe more space between the clutch discs is partly to blame? I think my clutch discs are pretty worn down.
My other thought is that when I pulled the oil pump cover to get at the shifter shaft seal, I was forced to use RTV to seal it up since you can't order a new CB900C oil pump gasket from Honda any longer. Nor can I find one on eBay. I can only find one for the F bikes and they are different. I'm sure the old gasket is slightly damaged since it was so brittle and desiccated from age and heat that chunks of it broke off very easily from above and below the oil pump. Perhaps the shape of the gasket is actually used to manage oil pressure?
The only other thing I can think of is maybe one of the oil pressure relief valves near the oil pump intake is stuck somehow; my Honda manual says this can lead to lower oil pressure. I was able to check one of them when I had the pan off and it seemed fine, but the other sat horizontally and I couldn't really get at it. I'll try to pull them off my spare engine so that I can see how they work and to see if they can seize up easily.
It's too bad though, I thought this would solve my problems but when I ran the bike for 20-30 minutes the issue came back. I'm thinking that when the oil heats up it becomes a bit too thin and the light is triggered. Again, this mostly happens when I hold in the clutch so doing that must change the way the oil is circulating internally. Maybe more space between the clutch discs is partly to blame? I think my clutch discs are pretty worn down.
My other thought is that when I pulled the oil pump cover to get at the shifter shaft seal, I was forced to use RTV to seal it up since you can't order a new CB900C oil pump gasket from Honda any longer. Nor can I find one on eBay. I can only find one for the F bikes and they are different. I'm sure the old gasket is slightly damaged since it was so brittle and desiccated from age and heat that chunks of it broke off very easily from above and below the oil pump. Perhaps the shape of the gasket is actually used to manage oil pressure?
The only other thing I can think of is maybe one of the oil pressure relief valves near the oil pump intake is stuck somehow; my Honda manual says this can lead to lower oil pressure. I was able to check one of them when I had the pan off and it seemed fine, but the other sat horizontally and I couldn't really get at it. I'll try to pull them off my spare engine so that I can see how they work and to see if they can seize up easily.
08-06-2015, 07:18 PM
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Re: CB900C oil light
If you can pull the strainer apart, I would do so. A lot of the time, you can't actually see the clog, and the screen can look clean, but the port is still restricted. The oil pressure relief valve can get stuck, and an easy fix for that would be to use a can of Motul Engine Clean. It's really easy, and removes 99% of the sludge in the engine. (just don't rev the engine once you put it in!) If the gasket on the pump is torn, that will lower your pressure, as there will be leakage from the pressure side of the pump back into your case. This is usually only an issue if you sit in traffic on a regular basis. Once the rpms come up a little, the pressure comes back up, and everything is good again. The clutch plates will have nothing to do with the pressure from the oiling system. There is no feed line up to the clutch. The oil just gets splashed around in that engine, and enough finds it way up by the clutch, and some draining down from the head will also find its way to the clutch. You could pull all the plates out and it would make no difference on the oil pressure.
As for the oil pump gasket, you can always use some generic gasket material, and cut one out to fit. I use x-acto knives, and a hole puncher for bolt holes. It seems to work fine for me, though it's not the prettiest solution. But who is going to see inside that engine?
As for the oil pump gasket, you can always use some generic gasket material, and cut one out to fit. I use x-acto knives, and a hole puncher for bolt holes. It seems to work fine for me, though it's not the prettiest solution. But who is going to see inside that engine?
08-10-2015, 08:01 AM
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Re: CB900C oil light
If you can pull the strainer apart, I would do so. A lot of the time, you can't actually see the clog, and the screen can look clean, but the port is still restricted. The oil pressure relief valve can get stuck, and an easy fix for that would be to use a can of Motul Engine Clean. It's really easy, and removes 99% of the sludge in the engine. (just don't rev the engine once you put it in!) If the gasket on the pump is torn, that will lower your pressure, as there will be leakage from the pressure side of the pump back into your case. This is usually only an issue if you sit in traffic on a regular basis. Once the rpms come up a little, the pressure comes back up, and everything is good again. The clutch plates will have nothing to do with the pressure from the oiling system. There is no feed line up to the clutch. The oil just gets splashed around in that engine, and enough finds it way up by the clutch, and some draining down from the head will also find its way to the clutch. You could pull all the plates out and it would make no difference on the oil pressure.
As for the oil pump gasket, you can always use some generic gasket material, and cut one out to fit. I use x-acto knives, and a hole puncher for bolt holes. It seems to work fine for me, though it's not the prettiest solution. But who is going to see inside that engine?
As for the oil pump gasket, you can always use some generic gasket material, and cut one out to fit. I use x-acto knives, and a hole puncher for bolt holes. It seems to work fine for me, though it's not the prettiest solution. But who is going to see inside that engine?
I was going to make my own gasket, but I found this one on eBay, NOS, so I think I'll trace out a few copies before installing it
My next thought is that I'll pull apart my oil pump and check clearances just to make sure everything is within spec.
I'll also look into that Motul Engine Clean. Thanks again!
08-23-2015, 10:02 AM
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Re: CB900C oil light
Update: After getting everything prepped for the install, I began monkying around with the oil pressure light wire. I'd already replaced the connector at the switch a while back and I was trying to see if my soldering job was holding up, when I accidentally broke the wire. Great. Just made a good night even better. This time, however, I decided to remove the starter cover to see if I could pull the wire out for a better soldering job. I am really glad I did, because I discovered that the wire had an exposed spot that was grounding out against the body of the starter! Ugh! I think this was my problem the whole time.
I fixed the exposed wire, got it soldered back up, installed the pump (making sure that it was engaged on the gear and the dowel was lined up correctly), filled it with oil and fired that puppy up! And the oil light flickered for a second before going out! At this point I was cautiously optimistic, so I reinstalled the shifter, foot pegs, etc and warmed it up so I could take out for a spin and voila! No oil light!
I fixed the exposed wire, got it soldered back up, installed the pump (making sure that it was engaged on the gear and the dowel was lined up correctly), filled it with oil and fired that puppy up! And the oil light flickered for a second before going out! At this point I was cautiously optimistic, so I reinstalled the shifter, foot pegs, etc and warmed it up so I could take out for a spin and voila! No oil light!
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