SOHC.co.uk Forums > CB750
Rewiring K2 with later high beam switch
K2-K6:
Just unbolted a UK K6 oil tank to look at the back/conections, bottom pipe is definitely conected to back of gearbox casing and reaches up to the top inside so if overfull it would "leak" into the engine.
Cam box breather just goes to air down the back of the engine, it could be US spec that had vents into the airbox to reduce emmisions as any oil mist would be burnt by the engine via intake which ties in with them pushing manufacturers first into that scenario.
It does seem like you've got yours to over pressurise itself and should at some point be vented to atmosphere to avoid a build up of crankcase pressure.
It would make sense for both top of oil tank and top of cam cover to vent into the airbox to contain emmissionsas this would probably create a small negative pressure in the engine.
the-chauffeur:
Thanks gents.
Looking at the various fiches, the K2's are showing as having separate breather pipes from both the cam cover and the upper rear of the oil tank. Of course, both are long obsolete, but the fact there are 2 listed, and the airbox doesn't have the breather entry point the later models come with suggests to me that both vent to air - and the advice I got previously was wrong. I reckon K2's right about emissions, and that over the life of the model range, at least one of the breathers was connected to the airbox.
With that in mind, I've swapped the cam cover breather hose for a longer piece and put a small quantity of sponge in the trailing end; just enough to (hopefully) catch drips and stop anything nasty going up the wrong way. I've also done the same to the shorter piece, the top end of which I've left connected to the top oil tank connector.
I guess that with the new routing arrangement the crankcase pressure should be significantly reduced - and that I won't need to pray too hard that the JB Weld will put paid to the leak.
Here's hoping . . .
K2-K6:
It'll be interesting to see how you get on and if it's leak free.
I was slightly puzzled that you had so many leaks compared to my experience hence the breather question.
Hopefully you've finally got all the bits sorted as they are nice to own.
Nigel.
the-chauffeur:
I'm still holding my breath and crossing my fingers . . .
. . . but I think I may have finally put paid to the oil leaks. Took the bike out for a 6-7 mile run today; not a major expedition, but enough to get the engine hot. No leaks and no squaks. Nuffink. I keep going out to the garage to see if it's dropped anything - force of habit - but so far, we're all good. After the best part of three year's work (on and off) I think I can maybe start relaxing about the engine.
I reckon that along with the filler, the massively reduced crankcase pressure levels won't trouble the top-to-bottom case seals any more. Which is a good thing. I'm still amazed at how close the JB Weld colour is to that of the cases. It's really, really close. As for the side covers, not even a hint of oil from them. And the 2.5mm o-ring plus a healthy smear of sealant has put paid to neutral switch leaks, too.
So thanks for all your help folks, although this isn't quite the last of it. It's time to start tidying the bits that don't look so, well, tidy and getting some (hopefully) worry-free enjoyment out of the bike . . .
Bryanj:
Well done, my personal opinion is that 90% of you leaks was the crankcase pressure mate, ride it and enjoy it now----sez he now it's 'kin freezing and going white!!
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