Topic: CB750K Oil Pressure Problem

[acb]

My oil pressure light is flickering on at high rpms (3000 +) after riding it fairly hard for 10-15mins.  If I continue riding it eventually just pegs red at similar rpms, no matter the gear.

However it's switching off when idling or in lower gears at lower rpms.  Also, if I stop and let the bike cool down for an hour or so then head out again for 20mins or so, never going above 4000 rpms before switching gears and never going above 3rd gear – it never comes on.

I've change the oil, oil filter and inspected and cleaned the oil pump strainer screen, and it's still behaving the same.  I know there's a lot of posts which say the indicator switch could be bad but it seems unlikely as it's not constantly coming on.   It's also worth noting that it seem to be working as expected before this happened – oil light would be on before starting and go off upon start or shortly there after. 

I'm not sure if this is related but I should note that my top end gaskets need to be replaced, so normally oil appears on the engine fins.  I have plans to fix this winter but I've been told from a few sources it's fine to ride like this, just have to watch the oil level.   

Seems like the next step is to get an oil pressure gauge but if anyone has any insight for troubleshooting it would be much appreciated.

[killersoundz]

I would personally invest in a oil pressure gauge that goes on the right oil gally plug. Can tell you what's going on more accurately.

[chewbacca5000]

I would personally invest in a oil pressure gauge that goes on the right oil galley plug. Can tell you what's going on more accurately.

+1 on the gauge.  That oil light has driven me bonkers only if I had gotten the gauge in the begging I would have saved myself alot to trouble.  As are as troubleshooting changing the oil pressure switch / sending unit is the only thing you can do. Some have removed and cleaned with mixed results.

[MCRider]

From personal experience and observation, 99% of the time an errant oil light is caused by a bad sensor, not lack of oil pressure. These are easy to change out, hardley worth any other fooling around until you do.

The seepage of oil from old gaskets will not drop your oil pressure.

Some sort of arterial wound would, but you'd have oil all over the place.

OCICBW, but i don't think so. 

[wrenchmuch]

Don't choose a gauge over the warning light . Having both is good as you can get some idea of how hot things are getting in stop and go traffic with a gauge .
Its location on the right oil galley is not the best for monitoring though . There's nothing like a light in front of your face to get your attention .

[acb]

Thanks everyone for the help, much appreciated. Gauge ordered and on it's way.  I'll give more details once I'm able to test.

[70CB750]

Oil presure does not flicker, it goes up/down but quick changes are likely electrical.

[Spanner 1]

Might be oil weight problem..... in Summer you should have 10-40 or 20-50 oil in there. If the oil thins too much due to heat, the oil pressure light might well flicker or stay on ...... IMO.

[Duke McDukiedook]

Change the sensor, odds are it is leaking by now anyway if it has not been replaced yet.

[acb]

Thanks everyone for the responses – I will keep these in mind as I continue to troubleshoot.

I finally got my oil pressure gauge installed and here's what I'm seeing:

When I fire the bike up, after about 30-60sec the gauge is reading 20psi.

However, once I start rolling the pressure slowly drops to 0psi and never really goes up again.  It comes up slightly at a stop but once I start rolling again, the needle falls back down to zero.

Also, no change with the oil indicator light – it's is still coming on/flickering after about 10mins of riding.

Seems like it could be an issue with the pump?  Anyone experience something similar?

[MCRider]

Thanks everyone for the responses – I will keep these in mind as I continue to troubleshoot.

I finally got my oil pressure gauge installed and here's what I'm seeing:

When I fire the bike up, after about 30-60sec the gauge is reading 20psi.

However, once I start rolling the pressure slowly drops to 0psi and never really goes up again.  It comes up slightly at a stop but once I start rolling again, the needle falls back down to zero.

Also, no change with the oil indicator light – it's is still coming on/flickering after about 10mins of riding.

Seems like it could be an issue with the pump?  Anyone experience something similar?

Wow that's not cool. 

Having just started mine from a rebuild, the oil light went out immediately and upon the 2nd or 3rd blip off idle the pressure gauge jumped to 70psi, I was expecting maybe 60psi. No more than 2000 RPMs.

I have a low , mileage oil pump from eBay. Seller said 7500 miles. i cracked it open and it looked brand new. HondaMan is refurbishing pumps with new Orings inside and out. I assume he's looking at the pressure relief valve too.

Don't know if there is something in the oil filter housing that could be messing you up. I don't understand the system quite that thoroughly.

[70CB750]

So you are saying that when the oil warms up, the pressure goes to 0?

I would check/replace/refurbish the oil pump now and if that does not help, you will need to rebuild the low end - replace crankshaft bearings

[Duke McDukiedook]

Drop the oil pan and check for the slack in the chain and inspect from below first.

[acb]

Thanks again everyone for the advice...

Got a new (used) pump from eBay, cleaned it and primed it (gave it a dunk in some 10w40 then spun the gear about 20 times). All seemed to be working well - spun smoothly and looked like it was sucking in oil correctly.

I installed the new pump and fired the bike up (idled at 1500 rpm for about 5-10mins)...and the gauge stays steady at 10psi.

Kind of wanted to take it out for a quick, lite ride to see if the gauge would jump up a bit more but was a little nervous since it didn'show significant improvement right away - any reason I shouldn't got for a ride and see what the gauge does?

All in all though, doesn't seem like good news

Don't know if there is something in the oil filter housing that could be messing you up. I don't understand the system quite that thoroughly.

Would love to know more about what might be happening in the oil filter housing - any ideas?

[Spanner 1]

Just how much do you trust that oil pressure gauge ??.... Think it's good ?

[MCRider]

Just how much do you trust that oil pressure gauge ??.... Think it's good ?

Yeah, I'm suspicious.

Are you getting oil to the rocker arms, esp 1 and 4 exhaust? Remove the caps, it should spit at you within 30 seconds. On the centerstand.

I missed it, is the oil lite working and did it go out on the last test running?

[acb]

Just how much do you trust that oil pressure gauge ??.... Think it's good ?

The gauge is brand new from Joker Machine (http://tinyurl.com/74ms9yq) - I feel like it's pretty trustworthy unless I installed it incorrectly? I installed it per the specs on the package (blue loctite on the threads, teflon tape on the gauge threads).

Are you getting oil to the rocker arms, esp 1 and 4 exhaust? Remove the caps, it should spit at you within 30 seconds. On the centerstand.

I missed it, is the oil lite working and did it go out on the last test running?

Oil light never came on at start up. After running for about 5-10mins I shut it down and the light came as it normal does after the bike shuts down. As I said  though I didn't take it for a ride so can't be sure if the problem with light coming on after a 15min ride is still happening.

As far as the oil getting to the rocker arms -  I'm a newbie at this, and I'm embarrassed to say I'm not exactly sure what those are or where they're located. Could you provide a bit more explanation on how to inspect? We are the caps for those located?

Thanks so much for the help!!

[Spanner 1]

Never did say what oil weight ( 10-30, 10-40, 20-50, etc ) your using and what ambient temps. the bike is being used in... ( bet it's 100 + deg ! ).

[acb]

Never did say what oil weight ( 10-30, 10-40, 20-50, etc ) your using and what ambient temps. the bike is being used in... ( bet it's 100 + deg ! ).

Oil Weight: 10w40

Ambient Temp: Today (7.7.12) was 75F, previous riding temps the past few weeks have been between 85-95F.

[Spanner 1]

Cannot be anything  wrong with your oil pressure if you rode your bike more than ( guess ) a mile without it seizing, just sayin' 

[acb]

Cannot be anything  wrong with your oil pressure if you rode your bike more than ( guess ) a mile without it seizing, just sayin' 

Yes, I've definitely rode more than a mile with the indicator light on and the gauge reading low pressure.

I also understand what you're saying but it seems strange that after the indicator light came on suddenly during a ride and then installing a gauge and getting a poor reading that nothing would be going on, correct? Am I not to trust either the indicator or the gauge?

Honest question: At this point (after troubleshooting and installing a new pump), if it were your bike would you feel comfortable rolling down the road with the indicator light blazing red and your pressure reading 10psi or below – or would you continue to troubleshoot?

Don't know if there is something in the oil filter housing that could be messing you up. I don't understand the system quite that thoroughly.

Are you getting oil to the rocker arms, esp 1 and 4 exhaust? Remove the caps, it should spit at you within 30 seconds. On the centerstand.

Would love to check both of the above (oil filter housing & rocker arm caps) out – again I'm a bit of a newbie, so not really sure what I'm looking for and if anyone could provide any insight on checking these, it would be much appreciated.

 

[MCRider]

If both the oil light and pressure gauge read low, I would not be comfortable riding it till I knew. 99.9% of the time its the light or the gauge, these bikes just don't fail like that, that's why you're getting the mixed signals from us. You could have that .01% er.

Especially with the new/used pump. Very unlikely two pumps had the same problem. Still...

My first step would be to get holt of a gauge I knew worked, or test yours on another bike.

Really weird, sorry.

Oil pressure i maintained by the pump and the main bearings and the rod bearings. usually losing pressure because of the bearings is the result of a catastrophic failure, not a slow wear down over time. Then pressure shoots 2 streams of oil up the backside of the cylinders and head where it goes into the cam bearings, squirts out on the rocker arms and becomes low pressure oil feeding back to the sump.

If you remove exhaust caps 1 and 4, and run it for a short time on the centerstand, the action of the rockers will flick drops of oil out and you know the cam is getting oil, as those are the end of the line for the system.

[Brantley]

Would love to know more about what might be happening in the oil filter housing - any ideas?

Gonna start with what is probably obvious- O-ring on bolt, bolt into housing, spring on bolt followed by thrust washer then filter.
I'm looking at the Honda manual right now... The pressure switch should turn the light off at 7.1psi. And to quote: "When operating the engine under extremely high oil temperature (over 244F, 100C [sic]), the warning light may intermittently come on at idling speed (800-900 rpm), however, this does not indicate a problem."
And, "If the oil pressure is 50 to 64 psi at approx. 3000 rpm and the oil temp is 140F, the condition is satisfactory."
20w50 will give you slightly higher pressure.
So, to clarify, your light is now out and you have 10 psi with a warm engine at 1500 rpm? That sounds right. You haven't said whether you've revved past 1500 rpm to see if the pressure on the gauge rises. If you have access to compressed air, aim some into the back of your gauge- if it don't go above 10 psi- bad gauge. (I actually just tried this with keyboard duster stuff and got near 40 psi).
If you didn't replace the 3 o-rings on the ports of your new/ old pump, it'd be a good idea. Sometimes that alone will restore pressure. They are 20mm o.d. x 15 i.d. x 2.5 w. Same size as the filter housing bolt o-ring. Honda gets a ridiculous $4 and change for them so try a local rubber and gasket joint. Grainger has 'em.
And Ron means "exhaust tappet inspection caps". On the valve cover. Rockers are under there and you should get oil all over the front fender if yr top end is being properly lubricated with these removed and the engine running.

[lucky]

Cannot be anything  wrong with your oil pressure if you rode your bike more than ( guess ) a mile without it seizing, just sayin' 

Good point SPANNER!!

[MCRider]

Cannot be anything  wrong with your oil pressure if you rode your bike more than ( guess ) a mile without it seizing, just sayin' 

I sympathize with that for sure.

Still, twere it me I'd need to know what's goin on.