Engine swap oiling question

[fiddlercrabus]

Hey all,
I recently purchased a '78 CB750F with a siezed engine. I have put in a '72 standard CB750 motor. There is a line that goes from the oil tank to the back of the motor/trans(not one of the main lines), and they are different sizes on the different motors. On the '78 F motor it was a fairly large line, like a 1/2 inch, and on the '72 mill it is much smaller, like a 1/4 inch. Will this swap cause any lubrication issues? Any info would be greatly apreciated!!!

[JonnyB]

Welcome to the site,

I think you may talking about the engine breather pipes, I have F1 and F2 engines and it is quite a large pipe, but I'm not sure how big they are on the '72 models...

These pipes basically allow gases out of the engine as its running. On the later models these are supposed to go into a diffuser under the battery box.... Something to do with reducing emmisions...

I'm currently running my F1 with no breather pipes at all, I suppose the only risk is that it could expell oil onto the back wheel.

Cheers John

[fiddlercrabus]

I see the breather tube that runs from the valve cover to the diffuser, but that's not the one I mean. The tube that I'm talking about runs from the oil reservoir to the back of the transmission. Is this just a breather for crank oil or does it supply lubricant to the gearbox?

[JonnyB]

That's interesting, neither my F1 and F2, oil tanks have a fitting for a breather.

This pipe must be overflow or breather, I certaintly does not feed oil, this is done solely thru the main oil pipes to the bottom of the engine.

[Voxonda]

fiddlercrabus wrote:

I see the breather tube that runs from the valve cover to the diffuser, but that's not the one I mean. The tube that I'm talking about runs from the oil reservoir to the back of the transmission. Is this just a breather for crank oil or does it supply lubricant to the gearbox?

Hey fiddler,

I know what you mean, I've got a'76 F1 and a '77 K6 both of them got 'big' breather pipes coming out of the back of the transmission. I also got a '72 K2 who has a smaller diameter breather pipe. Honda changed this because of the tendency of the older models to build up pressure inside the engine, so they made them 'breath' easier. It does not, at least should not, supply oil to the transmission.

Greetz, Rob