Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: PJCutts on July 06, 2020, 09:17:53 PM
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I have a 1974 CB750 K4 and have recently completed a full bike nut bolt restoration / rebuild. Having ran the bike for a few weeks (short rides only) noticed noisy clutch / gearbox. To investigate I had the Clutch cover and off and found the clutch to appear dry, upon running with the clutch cover off there was no sign of oil supply to the clutch/plates. Next step remove oil pump and check oil flow, turns out the was restriction on the scavenge / oil feed to the main shaft which is I believe how the clutch should receive oil. With that now flowing oil freely, put all back together and although it sounds better there is still not a large amount of oil flow to the clutch (or so it appears).
Can anyone please explain / show how much oil there should be in and around the clutch and plates? My understanding is oil should feed from the scavenge through the shaft holder and down the shaft, out the end and with centrifugal force oil the clutch. Should it be dripping with oil or only an oil mist?
If it should be dripping what could the cause of the lack of oil be (now knowing the oil gallery is flowing). When running with the clutch spider off you can see oil in the shaft but it doesn't seem to run out passed the aluminium bung.
Any help most appreciated
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Did you make sure you had all the bronze bushes on the gearbox aligned correctly so that all the oil holes line up 🤔
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Hi, yes I am sure I did as was very nervous of not getting that right. However I have now started wondering. I hope that isnt the issue! Just wondering how much oil there should be
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Hi, yes I am sure I did as was very nervous of not getting that right. However I have now started wondering. I hope that isnt the issue! Just wondering how much oil there should be
Being a dry clutch system ( as opposed to a wet clutch set up) there is never going to be a huge amount of oil there and TBH I wouldn't know how to describe or even take a guess at how to describe how much you should find. But, I would be slightly concerned it's not getting enough oil as you have found one restriction in the oil feed, maybe there is another restriction somewhere in the way of a debris blockage.
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I think Julie means "dry sump" as opposed to clutch.
I've not run one with the clutch cover off to see the flow, so no comparison directly to your observation.
However, it is the return side (scavenge) sector of the pump that feeds the geabox components by tapping off the route to oil tank. It's not a huge volume as I understand it, but obviously sufficient to keep all the components wet.
Clearly you won't get an oil "level" in the engine and gearbox as it's the dry sump design intention to exceed the feed in rate by pumping to the oil tank for the pressure side of the pump to use as a reservoir. Too much exiting through the box back to sump would be self defeating.
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In addition, presumably you're familiar with the characteristic noises this engine makes too?
Well setup and built, the engine certainly has a fairly unique sound to it because of the design. Have you changed the cam and primary chains for good quality new components?
Carb setting also being key to smooth sound, if at all rough it will oscillate the transmission (almost like having a remote flywheel with clutch and gearbox inertia clattering through primary drive variance) just holding the clutch in should reduce some sound as it disconnects the gears from drive.
But with it in first gear and starting to move it from standstill stops any transmission noise as tolerances are all pushed one way.
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K2-K6 'I think Julie means "dry sump" as opposed to clutch'
Yep, that's exactly what I meant Nigel 😁😁😁😁