The oil system and crankcase ventilation?

[ThoMoh]

I have a 750K3 with a K7 engine. I think the crankcase ventilation hoses and the valve cover are possibly installed incorrectly.

On my bike there is a valve cover hose and a crankcase ventilation hose. On the back of the oil tank there are two hose connections, the upper one a little thicker (same dimension as the crankcase ventilation hose connection) than the lower one and on the air cleaner (air filter holder) there is a hose connection which does not look to be original and could originate from the time when the engine was changed from K3 to K7.

Thank you for a description of how all hoses should be installed correctly.
Best regards ThoMoh

 

[pickleknuckles]

Valve cover breather line goes over the air box and vents to atmosphere near the swingarm on the K3.

Oil tank breather line (at top of tank) drops straight down and vents to atmosphere near the swingarm on the K3.

The small line on both the K3 and K7 goes from the back of the case to the oil tank it's actually an overflow a drain, not a vent.

Both breather lines on the K7 attach to a catch can that has a pinch drain on the bottom, vapor is routed back up to a fitting on the top of the air box on those bikes.

 

[pickleknuckles]

Fwiw, you can use routing for either model. If you have a K7 air box and decide to vent to atmosphere, you need to seal up the vent barb on the box.

On my K4, I didn't like how the vent lines misted oil right in front of the rear tire so I trimmed them and pointed them at the chain w some creative zip-tying.

 

[hinksy]

The middle pic is for the later motors . As of 77 on they had to basically have an egr , like a car . You probably have an earlier airbox , so I would just vent the head gasses out the back , just make sure it isnt breathing onto the rear tyre . I like pickles idea of a chain oiler

 

[ThoMoh]

Many thanks. Finally a Forum that works. My hoses were obviously connected incorrectly. I wish everyone a nice weekend!
Best regards!
Thomas/ Stockholm/Sweden

 

[dirtdigger]

Not egr but more like a pcv system. The valve cover tube is just a crank vent, I just put a small breather filter on my bikes rather then running the vent line back. A mechanically sound engine will make little to no blowby and you wont have issues with a filter or an open tube, if you have blowby I would look at putting some sort of a vented catch can on to collect the oil. The early model oil tank has a built in air/oil separator, the big line does vent to atmosphere, the bottom smaller one drains the separator back to the engine and I guess it could act as somewhat of an over flow. If the big line on the tank drips oil there is something wrong, probably having an excess amount of blow by that is overwhelming the separator and tank or a very excessivly over filled oil tank somehow.

 

[pickleknuckles]

the bottom smaller one drains the separator back to the engine and I guess it could act as somewhat of an over flow.

That's it! I knew it wasn't a vent and it returned oil to somewhere. Haha

Updated my post.

 

[ThoMoh]

Hello again and many thanks to everyone for sharing your knowledge. Much appreciated!

One comment on mounting the hose from the engine block (crankcase ventilation) to the lower pipe at the back of the oil tank is that they have different dimensions. However, the pipe from the engine block and the upper pipe on the oil tank are the same dimension. Does anyone know if the original hose (which is not available for purchase) has different dimensions at each end, larger towards the engine block and thinner towards the oil tank?

 

[pickleknuckles]

Pictures would definitely help.
It sounds as if there's a discrepancy between the K3 and K7 pipe sizes on either the engine or the oil tank.

The pipe from the back of the case and the bottom of the oil tank should be the same size. It is not a vent. It is a return line that drains back to the case.

The larger pipes at the back of the valve cover and the top of the oil tank are the breather vents.

 

[ThoMoh]

The oil tank is original K3 and the engine and engine block are K7.

When I took this apart, there is a thin hose on the lower pipe and on this a thicker hose from the engine block. All to enable the installation of a hose with the same dimension as the pipe from the engine block.

Could it have affected the engine that there was a restriction of the flow, i.e. the larger dimension from the engine to a thinner pipe (the lower) on the oil tank? The reason for my question is that the engine smokes a lot when it is started and is cold. It starts smoking on cylinder 4, then cylinder 3 and then all cylinders. When the engine it is hot it does not smoke at all. The engine is completely renovated, the cylinder bores honed, new piston rings, new bearings etc., etc.

 

[dirtdigger]

That wont cause your smoking issue

 

[UK K6]

Possibly oil in the head leaking slightly down the valve guides and pooling there after shutting the engine down?

Many old OHV British bikes are prone to this, but run for years without a problem. Maybe switch to 20W50.

 

[pickleknuckles]

The oil tank is original K3 and the engine and engine block are K7.

When I took this apart, there is a thin hose on the lower pipe and on this a thicker hose from the engine block. All to enable the installation of a hose with the same dimension as the pipe from the engine block.

Could it have affected the engine that there was a restriction of the flow, i.e. the larger dimension from the engine to a thinner pipe (the lower) on the oil tank? The reason for my question is that the engine smokes a lot when it is started and is cold. It starts smoking on cylinder 4, then cylinder 3 and then all cylinders. When the engine it is hot it does not smoke at all. The engine is completely renovated, the cylinder bores honed, new piston rings, new bearings etc., etc.

It sounds like the later K series bikes might use a larger I.D. hose than the earlier bikes. I suspect the later oil tank would be a similar size to the later engine.
Either way, it's a drain from the tank to the case and so long as it's connected, I can't imagine the size difference would cause any issues, certainly not the smoking you mentioned.