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I have made my ventilation box myself, but it “spiews” / leaks oil.
Not alarming but it is a bid nasty staining on the street.
My question for the forum is: does anyone have a flowing diagram of the engine/gear ventilation as it was on the motorbike.
I have to mention that I have a double spark plug conversion.
Any ideas

Henk
My engine is about the same age as yours, the vent box is of uncertain parentage, may have been from a T1, may not look anything like yours but principle will be the same. As my carbs are splayed out, I have plenty of room for the box and progressive throttle linkage.
The box sits on the 2 12mm sqare columns welded to curved holder then bolted to gearbox.
The front of the box sits on the crankcase breather, (which encases a large steel ball), breathing out but not in.
Top pipe at the front (no jubilee clip) is vented to ground but never drips.
Middle two pipes at front vent from rocker boxes, no restriction.
Then there is the mystery pipe just behind the crank breather pipe, which I have vented into a small container, cable tied to the crank breather. Not sure how far this pipe protrudes into the box but I do get some oil collected in the container over time.
Gearbox has it's own vent which I loop down to ground, but it never drips.
Not forgetting the reverse gearbox which needs a vent pipe taken up to a higher level with a catch pot. )I put mine on top of the petrol tank). This is essential as it does breathe out oil into the catch pot, which will be syphoned back to the gearbox as it cools provided the vent pipe goes to the botttom of the catch pot.
Hope this helps.

Hi Tony,
Thanks for the pictures and the description of the ventilation.
It surely is a good help
I think my engine breathing system is similar, the only difference is that my collector cylinder
Box is smaller in diameter and the piping from the rocker caps to the breaker are shorter.
I could try some longer hoses.
The reverse gear box breather is mounted inside the tunnel but higher up and with a loop in the piping, I don’t have any leakage from that set up.
I am using the original air filter housing (noise level otherwise to high) on my carbs.
Thanks again Henk

Weg wrote: ↑

Sat Aug 17, 2024 8:59 am

Then there is the mystery pipe just behind the crank breather pipe, which I have vented into a small container, cable tied to the crank breather.

Tony, the mystery pipe is the oil condensate return from the 'breather box' to the sump. It's attached to a pipe which feeds the returning oil to below the oil level in the sump.

I don't have a breather diagram (I think there may be one in Guzziology, which is a book you NEED, I'll have a look when I get a chance), but it's a relatively simple system. The vent pipe on the crankcase houses a loose ball non return valve, this allows oil mist out, but not in, to give a vacuum in the crankcase. Oil mist from here passes up into the breather box (sometimes part of the air intake trunking or frame on some models), where the oil is separated out to drip back down to the sump. Air is vented to atmosphere. On some engines, the rockers also have a vent to the breather, this is unchecked, just a plain pipe. It's there to give a free airflow through the rockerboxes prevent condensation and mayonnaise, but Guzzi themselves were unsure of the need; some bikes have it, some don't. Inside the breather box there is a flap valve to allow warm air out, but not cold air in, again to prevent condensation.

Hi Throwley,
I have checked my arrangement of the crankcase ventilation and the one of the gearbox.
I have special breather pipes on the rocker covers and connected like in Alan’s setup.
I think my breather box is much smaller than the one from Alan.
The hose I cannot understand is coming from underneath the original filterhousing and I have fixed it to the same housing as the crankcase ventilation box.
The gearbox is just like Tony’s stand alone with a filter at the end and mounted vertical to a “firewall”.
There are no drips of oil from that one, it is mainly from the crankcase ventilation.
I think my breather box is a too low volume.
But I am still very interested in the info you can provide on the motorcycle ventilation diagram.
Thanks in advance
Henk

Do you have this type of breather box (or similar but slightly larger aftermarket type)?



Aftermarket (Agostini)


In which case:
The pair out of top= breather pressure from valve covers (fixed to the lower large pipe on Agostini)
Large on bottom = Crankcase pressure in (from block)
Small on bottom next to large = oil drain (condensed back to oil in pan)
Medium on a slant out bottom = outside air/ pressure air out no oil(hopefully)

Another version is this integrated breather...



Which is similar to above except the rockerbox breathers are connected lower down and the air pressure out pipe is fed directly into the intake plenum, after the filter.

The Cali 3 uses the frame as the breather box. Crankcase pressure is fed into the frame, oil is separated and drained back into the sump. Rocker feeds, if there are any, I think are fed into the air filter plenum as is the pressure vent from the frame. Sorry, can't find a decent illustration of this one.

So, essentially the breather system uses different components in each case, but serves the same function:
- a one-way valve lets pressurised oil mist out of the crankcase
- this enters an oil separator box, where the oil condenses out
- condensed oil runs down a pipe into the sump, below the level of the oil
- separated air is vented from the separator box; this is sometimes dumped overboard, sometimes recirculated to the intake tract
- sometimes vent tubes from the rockerboxes are fed into the separator box (and sometimes into the air filter, and sometimes into the crank vent pipe)
- sometimes the separator box features a non-return valve on the vented air outlet to prevent cold, damp air being drawn into the separator box

I've not managed to get to my Guzziology yet, but it is still on the list!

Thanks Throwley,
This is good information, I know that the breather from crankcase and valve covers went into the frame, so the Small oil pipe is probably the return from the condensed oil mist back in the crankcase somewhere under the air filter box, i haven’t checked that one yet.
I know the oil drip is minor and not alarming, it is just annoying on my drive.
Thanks Henk

Henk, finally I got to it...



as a '92, yours is the lower image.

What I didn't realise is that the return oil path on your model is via the rockerbox breather pipes, rather than directly to the sump.

Thanks, that’s it, good info.
Now I can reroute the hoses in the correct way, great help.
Henk