head breather to exhaust

[mick77]

I found this in The Horse mag,

" With the head breathers hooked to the exhaust, the exhaust will create a vacuum and help suck the crank case pressure out of the motor. With these tubes sticking into the ends of the pipes,it helps break up the exhaust pulses,making the bike a bit easier to tune."

[tomterrific]

Yep. Running a vacuum in the crankcase has a bunch of benefits. The first most folks think of is an increase in power. I learned about the exhaust sucker type breather from articles in which Grumpy Jenkins told how his secrets worked. Both my Triumph T140 and my XS650 use power brake booster check valves in the breather hose so the pistons pump the crankcase out but the valve checks when the pistons go up. My primary concern is oil leaks from old dry gaskets. Both engines are mechanically fine but old gaskets and seals are suspect. Note that some of the top Vintage racers use teh exhaust sucker as you discribed.

Tom Graham

PCV valves do not work in a motorcycle breather hose. The PCV system of a car is totally different in concept and the valve checks in both directions so can INCREASE pressure in the crankcase. Don't use a PCV valve in the breather hose of a bike.

[mick77]

Thanx Tom! I'm going to go with it. Should I also add the check valve that mikesxs has? I've also noticed a small amount of blowby on mine and I'd rather have that oil being burned up in my exhaust than making a mess on my motor.

[tomterrific]

Mick,

Do you have a '77? Put the important stuff about your bike in teh side bar like I have. You can get there with your Profile.

My '77 has two breather hoses that are 1/2". You can get a 'power brake booster check valve' that is cheap ($5) and perfect for the job we want from Advance Auto on the Help rack in the aisle of the store. The 1/2" nipple of the valve plugs right into the 1/2" hose running off the breather. The other nipple is 3/8" and I found vinyl hose plugged onto that nipple. You can route this to the ground or it will fit inside 1/2" hose if needed to feed into the stock air box. Remember the air needs to go out of the crankcase but not back in. Don't get the check valve backwards. You can try to make exhaust suckers but they will be allot of work and may not be a help unless racing.

Tom Graham

[5twins]

So, Tom, do you have this check valve on just one hose or both (2 check valves)? I have my 2 hoses run to a brass "T", then down to a K&N breather filter. I'm thinking I could add the check valve in the single line that runs to that filter (if it's not too big). Hose size differences could be addressed by using smaller hose "sleeves" over the valve nipples so it would fit my current single hose I.D. Here's my set-up now with a 3/4" single hose to the breather filter .....

[mick77]

Hey guys, My main reason to go with the exhaust is that I'm having oil blowby coming out on my motor.Not alot,but enough to see. Is that caused by worn rings?

[kiwi]

Tom. I don't know about putting the restriction in breather. I am familiar with the booster one way valve, but it will create a negative in the case when the pistons go up, is that a good thing, especially with old seals and gaskets. But you reckon it's been working on your Triumph, so can't be that bad. I would just get rid of that rubber plug that Yamaha found necessary to stick in the breather block, route the lines away from the motor. Mine run along the top frame rails and exit out back, or do as 5twins did. John.

[tomterrific]

Hi 5twins,

The brake booster check valve is a 90° bend which can help or hinder an installation. I'd like to find a suitable check valve the has straight nipples. The 3/8" hose sleeve to 1/2" is what I was trying to describe. You did it better. I haven't ran the Triumph long with the check valve and it is cold now but other Brit bikes run the valve with good results. The Triumph seemed like it ran freer on the highway at 70 mph but that could be the cooler weather as well. I'm not sure a breather filter is needed since the direstion of gases is only out of the breather hose.

Kiwi John,

I have in mind a more sophisticated positve ventilation system in mind that will pump air through the crankcase to vent it of moisture and combustion by-products but still keep a slight forced vacuum in the crankcase. No restriction in my '77D breather really. I use two valves and pulled the blocking pieces of hose from the breather box on the head. Remember the amount of air/gases the breather system passes is much lower with a one way valve checking the intake of air into the crankcase.

Tom

[Six-Five-O]

Tom..I have installed the single outlet breather set-up on the 78-79 engine that currently resides in my 82SJ which retains the stock airboxs..I have hogged out the single outlet, plus enlarged the hole in the restrictor plate and have a single breather hose feeding a T-Fitting, that in turn, provides venting into the right and left airbox breather inlet nipples...I presume a single power brake bleeded valve would be all that is needed on a stock airbox set-up on the later XS-650s?

Great info...I think this needs a sticky!


Best Regards

John

[Burns]

has anybody actually dyno'd a before-and-after on this? Seems like if venting the crankcase to the exhaust gave any benefit ALL m/c racers would do it (well at least all the 4-strokes).

[mrriggs]

My base gasket leaks badly. The front of the case would get soaked and it would leave a large spot on the ground anywhere it was parked. I tried the check valve and it made a huge difference. It still leaks a bit but not bad enough to drip on the ground.

[pamcopete]

Well, is it possible that if there is a vacuum in the crankcase there would be a tendency for the oil on the cylinder walls to get "sucked" down? In other words, would the vacuum contribute to blow by and a reduction of lubrication on the all important cylinder walls and rings? Or, to put it a third way, would there be a lessening of distribution of oil on the cylinder walls during the intake stroke when the combination of vacuum in the cylinder head and pressure in the crankcase draws oil up to lube the rings?

When these types of issues come up, I always think about the 1,000 engineers who designed the XS650 and wonder if they didn't know what they were doing. I think that this situation is the reason for the design of the PCV valve. The intent was to draw unburned hydrocarbons into the intake manifold to burn them up, but not create a large vacuum in the crankcase.

[Burns]

Isn't the PCV just a check-valve, i.e. a one-way passage? If so it seems that its purpose is to vent the crankcase under positive crankcase pressure but not allow fuel/air misture to get sucked into the crankcase on the negative pressure end of the cycle.

But, to follow your 1000 engineers train of thought, it seems unlikely that they all would have overlooked any positive benefit of venting crankcase pressure to the exhaust. Multiply that times all of the other 4 stroke engine applications engineers who seem to have overlooked this benefit for what, a 100 years?

I gotta see some dyno numbers on this one before it comes out of the "Garage Legends" file for me.

[5twins]

Well, I did the deed. I installed the brake check valves on my breather hoses and positioned them over my pods so any vapor will just get sucked into the carbs .....



I also re-installed the rubber restrictor plugs in the breather outlet nipples. My bike has always used some oil. When I rebuilt the top end last year, I was hoping this situation would improve but it hasn't. I pulled the restrictor plugs when I first got the bike running. Everyone said it was OK to do so. Well, I'm not so sure anymore. I think my motor was breathing too well without them, blowing out more oil vapor than it should. While the breather filter I had installed never actually dripped oil, it was always wet looking.

There's a page over at 650Motorcycles.com that promotes opening up the smaller one outlet breather on the later motors. I guess that removing the rubber restrictor plugs on the older 2 hose breathers is sort of doing the same thing. Now this may be fine and maybe even necessary when racing but I'm starting to think we don't need this on our street motors. 650Central just put up a bunch of articles by Farrell Hope, a long time 650 enthusiast. He has one on excessive oil blow-by and it's worth a read. He feels as I'm starting to that opening your breather more will do nothing but blow too much oil out.

[NIGHTMARE]

Where did you place the breather hose in the header and what fittings and hose type did you use to take the heat ? I've done this on cars and it worked great.