Topic: 2 pipes out rear of K1 crank case

[Timboslice]

Hi folks,

I’m nearing the end of my CB750 k1 build and attempting to fit the hose from the crank case to the oil tank. It turns out that there are 2 pipes coming out of the crank case. Logic would tell me that both pipes lead to the two pipes that come out of the oil tank, however my understanding was that the larger diameter pipe on the oil tank is a breather and doesn’t attach to the engine. Other cb’s that I can find only have one pipe exiting the rear crank case as an oil overflow.
Does anyone know why I have two pipes on this engine? And what the larger diameter one attaches to? If anything…
Thanks. Photo attached.

[Don R]

 I think the top one was added but I'm not sure why. I noticed the oil line on the left going up front. Or is that the starter cable? Maybe there were some custom changes made by a PO. Is the rest of it pretty original?

[scottly]

Don is correct that the larger top spigot was added, and yes, the larger spigot on the oil tank is a breather, open to atmosphere. The hose is routed down on the right side of the swingarm near the pivot, along with the breather from the cam cover. Both breather hoses should be held to the side of the tire, lest any oil/condensation should drip out.

[Timboslice]

Thanks guys.
 Yes that is the starter cable.

I built the bike with parts from many. I have only just realised that this is not stock… maybe I can just plug that hole…

Cheers

[scottly]

You could also use it as an additional crankcase vent, with a 3rd hose?

[Timboslice]

Wouldn’t oil come out of it? Or run a hose up high?

[ekpent]

 Wonder why the heck someone went to the trouble of adding that ??