Alternatives to breather box?

I’m not sure what the differences between the types of breather box are, but has anyone managed to dispense with one entirely? (Maybe using a K&N - type mini filter?)
ThanksMr Noisy2014-06-13 20:48:34

Not a good idea. I had the big hose come detached on the Spada, lost half it’s oil and partially seized. Expensive and long winded to fix. If you want K&N’s best bet is use the Le Mans style collector. To make even more sure oil doesn’t escape, add a sump extension. The increased volume reduces the pumping action to blow it out especially at high rpm. Which is where oil loss problems via the breather can typically occur.

But can’t eradicate the breather box entirely IMHO. Hope this helps.

What model are you talking about? Later big blocks use the frame as a breather box. Maybe you could do something along those lines.Dumping the standard air filter and fitting K & N’s is a good plan. Very few on here still use the original air filter, box etc, but as Mike mentions above, you should really fit a Le-mans style breather box to collect up all the vents and return any escaping oil back to the sump…

I have a 81 Spada, which I’m converting to cafe racer similar to Kaffee Maschine. I’ve carb K&Ns anyway, but the filter I originally mentioned is as I had on a Ducati - just a small unit that clipped to the crankcase breather stub. I’m trying to ‘clean up’ all the clutter between the cylinders.

I’d assumed he’s talking about the old style as he mentions breather box

My mate Batty tie wrapped a small Guinness can to the frame as a breather collector on his Mk I Le Mans as it matched the colour scheme of the bike

I wouldn’t rely on just one of those though, unless it was just to catch any drips from the normal vent pipe, as it would also need all the other plumbing to recover the oil blown out of the crankcase. Which it will be. MG did put a lot of thought into the crankcase breather system, it wasn’t just thrown together.

Whic is the most compact box then? I’ve a spare LeMans unit, but is there anything any smaller? I think you are better with the replacement ball valve also?

LM unit is it I think, but doesn’t show that much. Yes you can use the ball valve with it.

I thought that the LM unit is the same as the Spada/T series one. I think that Guzziology suggest that you do away with the valve, please correct me someone if this is wrong?

My Spada unit is larger & has a ‘hole’ thought the middle, front to rear. I assume for part of the air filter, though mine has always been missing. Guzziology recommend removing the internal flap calve & replacing with a ball valve. Just got to track that down now.

Yes depends if model has the std conical paper air filter, then as above. Le Mans, no filters, totally different construction PS: (edit) I couldn’t be asked trying to get the flat valve out, knowing my luck I’d just cock it up, so left it but have always included the ball valve as well. As has been said before best way to prevent oil loss out the breather is a sump extension but keeping the std max. of 3.5 litres of oil. Also wotsisname Roper said so.
Mike H2014-06-17 17:15:36

Guzziology recommends using the later version of the ball valve in the top of the crank breather hole and to disable the flap valve in the breather box as this can jam shut. I must admit I have the flap valve and no ball valve in mine. It does blow a bit of oil out the dip stick on a long run, just enough to leave a fine trail down the fairing lowers.Sounds like your Spada still has the original air filter unit (or at least part of it) Chuck this in a cupboard under the bench and forget it.

This is the std Le Mans style. Note that the rocker cover banjos have to be at the front with this one.

Are the rocker cover breathers necessary or can it breathe down the pushrod tubes?

I am sure they fitted them for a reason. When the crankcase is pressurised on the down stroke, the rockers are a sealed space so the vents would allow air to escape. There are no oil seals up there to give concerns, but you would still have the holes, I guess you could just put some blind bolts in them.

Actually when the crankcase breather hose is closed by the ball valve, by crankcase going into vacuum (pistons rising), this also then: A. sucks any exhaled oil lying in the breather box back down the drain tube to the sump, and: B. sucks air up the rocker hoses into the rocker boxes and thence down the pushrod tunnels AND also the separate drain tunnel in each head and barrel, i.e. helping to clear surplus oil out of the rocker boxes. I imagine excessive oil levels in the rocker boxes would encourage leakage down the valve stems, and therefore oil loss, excess smoke and carbon build-up in exhaust etc. This is why I say somebody has spent some time working it all out. Modify at your peril!
Mike H2014-06-20 16:30:45

Good point. Thanks!

The Agostini breather as mentioned above is a nice little unit and good compromise between declutter and function. I’ll be using it on my Le Mans 2 special. I also wanted to not have to use rocker breather lines as I’m using early loop rocker covers, but think as Mike says best not to detour too much away from how it’s all meant to work, so I’ll probably tap’ em and add breather tubes…

I wish the smallblocks had someting similer.I am fairly certain the oil loss is through the rocker breathers when the engine is used hard.Tim Hicks, your enginuity is required.