Hi All, Until HD employ decent technical writers, who include say, a diagram in one or both Sportster manuals..., can anyone please advise on how the cases are breathed? My local Sydney agent cannot. He didn't even know about the gearbox breather, until we found it!
Sofar, I've mapped at least FIVE engine breathers...
1/ Two top end breathers venting blowby into my carby. That is great for the environment but bad for engine longevity. They will be redirected as my warranty ends, to atmosphere via a socially-responsible filter!
2/A tube connecting the oiltank into my cases. In the Service manual, that's helpfully labelled as..."a vent". Yeah, that's really helpful...BUT is it a 1 or 2 way vent? Does it have a valve? Is it venting the cases or oil tank or both? I guess it's venting the pressurised oiltank, and/or returning oil to the cases. If true, it's also contaminating the oiltank continuously with noxious, corrosive blowby. Another minus for engine life, and great for oilcos!
3/ A tube joining the carby intake ( clean side of filter) into the cases. I assume this is an inlet breather, balancing the air lost via the two top breathers, and the oiltank line. Again HD technical writers are silent on the matter.
4/ A gearbox breather, venting just behind barrel 2. Again HD have nothing to say about this. My dealer didn't know it existed. Has anyone mapped this curious, complicated and almost certainly damaging and ineffective system? Thanks Bunny32, downunder.

Only 2 posts! Welcome to the board.

I can't answer all your questions about the various vents on the motor / tranny, but as far as the engine is concerned, all crankcase gasses are routed up to the heads and then into the airfilter.

That's where a problem exsists. If you want to change anything, dump the stock airfilter and get a breather that routes these crankcase gasses to atmosphere. There really is no reason to use a small filter in the line that runs to atmosphere. Just let the hose terminate below the lower frame tubes on the bike.

Here is my carb with an aftermarket U shaped breather. That rubber hose just vents below the bike .... No more oil vapors getting into the carb and gumming up the slide or making carbon deposits on the back side of the intake valves and pistons.

http://x10.putfile.com/4/9618143443.jpg

Dude - don't overthink it, it's just a Sportster!

Hi All, Until HD employ decent technical writers, who include say, a diagram in one or both Sportster manuals..., can anyone please advise on how the cases are breathed? My local Sydney agent cannot. He didn't even know about the gearbox breather, until we found it!
Sofar, I've mapped at least FIVE engine breathers...
1/ Two top end breathers venting blowby into my carby. That is great for the environment but bad for engine longevity. They will be redirected as my warranty ends, to atmosphere via a socially-responsible filter!

You got #1 right


2/A tube connecting the oiltank into my cases. In the Service manual, that's helpfully labelled as..."a vent". Yeah, that's really helpful...BUT is it a 1 or 2 way vent? Does it have a valve? Is it venting the cases or oil tank or both? I guess it's venting the pressurised oiltank, and/or returning oil to the cases. If true, it's also contaminating the oiltank continuously with noxious, corrosive blowby. Another minus for engine life, and great for oilcos!

That is just a hose that equalizes pressure between the engine and the oil tank. Without it, the pressure differences could cause the oil not to flow to the motor. The motor is gravity fed, so it can't have a vacuum in the tank, and the tank is not vented to atmosphere. The motor is vented, sort of, via the breathers at the air cleaner, but it's not enough to equalize the pressure between the tank and the motor. There is no check valve or anything. It's just a hose!


3/ A tube joining the carby intake ( clean side of filter) into the cases. I assume this is an inlet breather, balancing the air lost via the two top breathers, and the oiltank line. Again HD technical writers are silent on the matter.

I gotta say I don't know what that one is. Maybe there is some emissions stuff on the Aus model, like California? Post a pic?


4/ A gearbox breather, venting just behind barrel 2. Again HD have nothing to say about this. My dealer didn't know it existed. Has anyone mapped this curious, complicated and almost certainly damaging and ineffective system? Thanks Bunny32, downunder.
That vents the pressure from the trans and primary to atmosphere. Nothing sinister there.

You are WAY overthinking the whole thing. The only issue performance wise is as Turbota posted: the oil vapor going back through the motor through the intake. Fix that, and there's nothing else to worry about in the oiling or venting system

--Chris

Thanks Turbota and Chrishajer for your useful advice... that I'll take. I mostly restore and ride classic British bikes, and came late to Harleys. I design and sell breathing systems for classic bikes, hence am unusually interested in how things breathe. From your advice, I plan to install banjos inside the hamcan airbox, take a T-union out through the plastic back plate, and drop it to ground as you suggest, whilst retaining the OEM intake setup. As for the oil tank breather, I'll drop that to ground as well. I'll check into that small breather linking airfilter and cases and advise further....bit too crowded to get you a pic. bunny32

As for the oil tank breather, I'll drop that to ground as well.
There is no "oil tank breather." There is a vent line from engine case to oil tank that equalizes the pressure. That connects the two components and should not be disconnected from either end.

If you mean the transmission/primary vent, that is already vented to atmosphere under the seat, and if you run it down, to the ground, instead of up, lots more oil dumps out.

I would follow Turbota's recommendation and modify the head breathers and leave it at that. Any other mods will do you no good, and in the case of the oil tank vent, will hurt things in a big way.

Any pics of the brit bikes? My last was a 1969(?) BSA 441, and before that a 1974(?) TR7.

--Chris

Hi again Chris, what a coincidence. I specialise in BSA Unit Singles. Here are a couple of my restos, a 1970 B44SS, a lot like yours, 'cept mine is the less common B44SS roadster.The 1971 T25SS is an odd one too, came from Cycle Hub, Portland, into NZ where I restored it. It was a NOS bike under the grime!
I'm doing a B50SS now and an OIF TR6. Today is a big day for me as I now own a motorcycling patent for a new engine breathing system, I developed for classic bikes. You can see why I'm interested in Sportster breathing, as I plan to install my Kit on it as well, and intend using the lines we're discussing, but in rather new ways. Rex

Yeah, there was nothing uncommon about mine. They were your average, run of the mill, $100 motorcycles.

Nice pics, and congrats on the patent. I'd like to see what that is.

--Chris

I would be interested to know if your breathing system would work on my '66 BSA 650 Thunderbolt. I've never been a fan of the breathing system on that bike. And welcome to the XLF from the Canadian prairies.:)