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Old Streetfighter Motorcycle Forum Post 01-18-2013, 05:14 PM   #1
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Default Honda CB750 oil pressure issues

ok, so i know without having a gauge to go off of this may be me over reacting... but... i was on a 30 mile run into town the other day and i noticed when i came to the first stop light that my idiot light was on at an idle, reved it a few times and it went off... till the bike got under 2000rpms them it came back on. its unknown what the pressure is as i havent been able to afford an actual gauge yet which is where i really need to start at for a decent diagnosis. running 20/50 GTX in it. Any common issue or problems i outta be aware of with this bike that i didnt know about before? I know of the pump O-ring issue and replaced them already and its still doing it. any possibility of it being a bad sensor, bad pump, or spring weak in the high pressure valve on the pump? any suggestions would be great. I'm just praying its not a main bearing... but, no shavings in the pickup, filter or pan(just pieces of clutch... but not enough to block the pickup... what i consider a "normal" amount.)
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Old Streetfighter Motorcycle Forum Post 01-19-2013, 05:16 AM   #2
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Default Re: Honda CB750 oil pressure issues

You mentioned the oil pump o-ring issue so I'm assuming you have a SOHC. If so, those o-rings were gonna be the first thing I was gonna suggest. In all honesty, the idiot lights are not all that trust worthy, but they ain't all bad either. It may just be time for an oil change. These old airheads are pretty hard on oil. I dump mine every 2K miles in hot weather. Filter every other time. Do you have,the adapter for the upper oil gallery to mount a gauge? If not, there's enough meat in the stock plug to drill and tap it for one. You can save a few bucks that way.

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Old Streetfighter Motorcycle Forum Post 01-19-2013, 05:20 AM   #3
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Default Re: Honda CB750 oil pressure issues

Oh, if you saw pieces of clutch you need to check that ASAP! The outer plate is famous for delaminating on these (still assuming you're rocking a sohc) and if left unfixed will dig up the soft aluminum pressure plate FAST! Don't let that go unchecked. You can get that plate as a single from Barnett for $15. It has different oil shed grooves than stock and seriously improves the feel of the clutch. It'll chatter like a bitch, but...clutch.chatter is sexy

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Old Streetfighter Motorcycle Forum Post 01-19-2013, 06:21 PM   #4
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Default Re: Honda CB750 oil pressure issues

Yeah I plan on looking into the clutch issue soon, have heard a rumor around town they my oil lines have been sabatoged by this skinny little tweeker who aparently has a deathwish. so gonna check into that, havnt seen any leaks in my lines though, alos yeah is a SOHC 836cc. And the oil thats in it only has like 300 miles on it. Im pulling the oil pump to see if there have been any objects thrown in my oil tank than may have been sucked down in my pump. But good call on the oil cap drill/tap project, will be one i start soon now. and seeins how i have 4 or 5 of these engines laying around, could always just pull the plug from one of the others and start in on it. Thanks again, will keep posted on my findings.
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Old Streetfighter Motorcycle Forum Post 01-20-2013, 02:12 AM   #5
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Default Re: Honda CB750 oil pressure issues

Cool. I'm working on putting together an 836 myself. What cam are you running? And whose pistons did you use? I'm having a hard time picking out a cam. I'd really appreciate some advice. Catalog descriptions of cam characteristics dont mean squat to me. I'd rather hear it from the guy behind the handle bars,than the guy behind the computer
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Old Streetfighter Motorcycle Forum Post 01-20-2013, 05:33 PM   #6
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Default Re: Honda CB750 oil pressure issues

still has a stock cam in it for now. but they are a wiseco piston kit. ended up being bored out after someone else toasted the original cylinders and head on it. I have a 69 here that has a cam in it, but i have never ridden it.
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Old Streetfighter Motorcycle Forum Post 01-21-2013, 12:08 AM   #7
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Default Re: Honda CB750 oil pressure issues

Heres the original pull apart to show the conditions of the O-rings that i changed last week.

This one was never installed correctly.





So, after giving myself a few day cooloff period before touching the bike again. pulled the pan back off, pulled the pump and got it apart. the problem was pretty self explanitory.



Faces are scarred.


Rotors are wasted.






So, cleaning the entire system and tank out, and pulling the pump off my parts bike and cleaning it out and gonna swap it on after changing the O-rings again.
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Old Streetfighter Motorcycle Forum Post 01-21-2013, 01:51 AM   #8
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Default Re: Honda CB750 oil pressure issues

Bummer! Good luck with it boss
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Old Streetfighter Motorcycle Forum Post 01-21-2013, 03:26 PM   #9
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Default Re: Honda CB750 oil pressure issues

And The stupid light still comes on under 1500 RPMS when its warm now, but its better than it was. I have a thought that maybe the odds are that the filter is clogeed and the bypass isnt opening as much as it needs to at an idle may be a little high. Also beginning to wonder if my fuel soaked oil is just already burned up and wasted. its already black. so gonna try an oil change next. Also im not sure if the Orings i changed are the right ones either. honda calls for 15X2.5mm and the ones i put in there are 15X2.0mm Not sure if that extra .5mm in width makes a huge difference but. who knows, it is trying to hold back 70+ psi of oil pressure. If not, im back to square one and thinking the worst... that im losing a main bearing and have to split the case. I also read something somewhere that the head studs on these stretch and need to be retorqued or it wont hold pressure, but i also read if that was an issue, the oil galleys on the back of the head would be leaking from the head gasket onto the back of the engine. so IDK... its pissing me off. I just wanna Ride. :'(
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Old Streetfighter Motorcycle Forum Post 01-21-2013, 04:12 PM   #10
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Default Re: Honda CB750 oil pressure issues

What kind of oil pressure does it run at highway speeds? Not trying to be a jerk but you gotta a gauge on that thing or you'll be chasing your tail for a long time.

Hell, you might find your oil pressure is spot on and only the idiot light is acting up.

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