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Sportster Motorcycle Air intake, Carburetor, EFI, Fuel, and Exhaust Problems, advice and/or how tos for Sporster and Buell motorcycle carburators, Electronic Fuel Injection (EFI), Air Intake, Fuel and Exhaust.

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  #21  
Old 28th December 2015
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No not getting rid of the umbrella valves. The only thing I'm trying to do is move where the vents exhaust.
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  #22  
Old 28th December 2015
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My personal theory is that HD went to the tiny breather holes to try to build a little crankcase pressure, to help with scavenging. Wet sumping has been a problem with these motors for forever, and it's well known that low crankcase pressures aggravate it. Hell, every motor I've ever set up with gapless rings wet-sumped like a pig.

So at one extreme, with a restrictive breather, you're increasing the risk of an oil leak, and at the other extreme, an unrestricted breather, you're increasing the risk of wet sumping. Those are the things that are framing your decision on the hole size.
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  #23  
Old 28th December 2015
rubine rubine is offline
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What Ive thought could be a good idea would be to vent into a frame, a hollow sealed frame, but I guess it would have to be a large diameter frame so your increasing the volume of the crankcase, and using the frame as a shock absorber at the same time, so the pumping may have a lesser effect on things. Maybe have a one way valve somewhere, and a drain tap at a low point. Just a thought...
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  #24  
Old 28th December 2015
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Quote:
Originally Posted by rubine View Post
What Ive thought could be a good idea would be to vent into a frame, a hollow sealed frame, but I guess it would have to be a large diameter frame so your increasing the volume of the crankcase, and using the frame as a shock absorber at the same time, so the pumping may have a lesser effect on things. Maybe have a one way valve somewhere, and a drain tap at a low point. Just a thought...
That is exactly what i did with my 05R. I vented it on the top of the frame with a small sintered brass air muffler.
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  #25  
Old 29th December 2015
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Quote:
Originally Posted by nicksta43 View Post
I understand how crankcase venting works. I also am of the opinion that I don't want it recirculated back to be ingested by the engine. My only question was if the holes in the stock vent bolts are big enough. You are arguing points that are not even close to the scope of the question.
The problem with asking a question on this forum is you get 10 different answers. Then you are left with finding out the answers that work for you.

I agree with you, I do not want oil vapor getting into combustion chamber. I would think the small holes in the stock breather bolts are matched to the umbrella valves, which are generally considered to be only marginally effective, leading to so many problems. As long as the umbrella valves work, the cheapest thing to do is run tubing from them to outside the air filter. Problem with that idea is when they umbrella valves fails, and they seem to fail fairly quickly without warning, you can coat the side of the engine with oil. Drilling out the hole in the breather bolts can only aggravate the problem when the umbrella valves blow out.

I would guess, drilling out the banjo bolts will not help much until you get a good one way Krank valve hooked up to them. I would also guess that if you add after market external breather kit with proper banjo bolts and external Krank vent now, you can always add a cam vent in the future if you decide to go with a big displacement engine.
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  #26  
Old 29th December 2015
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first of all, there isn't a great amount of vacuum inside the cleaner. the media MUST be able to flow way more air than the engine can consume or the mix will be WRONG. this was discussed in another tread, I believe lube section. at low throttle, the vapors will exit the holes and then go lazy and drop out since flow is low. the best is when the throttle is fairly open. vacuum in the cleaner has nil effect on the breather system. without the coalescer working properly, excess oil can build and not drain back so keeping the system clean will help, aka, proper oil maintenance. also, here is where high c/c pressure can effect the drain back since everything flows up to the heads.
most all machines go to the cleaner. if you put the vapor in direct contact with flow, it has way less chance of going lazy and dropping out. think of the breather bolts as a venture. when the vapors pass through the hole, it must accelerate in speed and when it goes to the low pressure, velocity drops and it can not contain particulate matter and it drops out. just like a carburetor when slammed open, atomization wanes and fuel drops to manifold floor.
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  #27  
Old 29th December 2015
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Bustert gives a good answer here. If you have an XL with a timing plug under the aircleaner you can pull that out spin a threaded fitting in there (might be NPT) and run another hose from there. I have been looking at the after 2004 case and HD bores new holes and closes others over so to fix this I would pick up a spare rocker box top cover which is very light and thin and mount an 90 degree elbow, well sealed and pointing straight back to a catch can. Make sure you are not interfering with the ends of the rockers. If you like it run another from the other rocker box too then plug the breather bolts or replace with the right size. The oil will drain down, the air cleaner will stay clean, you will not look down and see a serious oil leak on the right side of the engine and the vapor leaving the engine will be a lot cleaner. You can run the hoses along the frame rails with a filter at the end if you want to skip the can. Nice big hose with 5/8 ID. This will not cost a lot of money.
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  #28  
Old 29th December 2015
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You don't want to allow the crankcase to inhale air. When you do that, you end up with a large exhalation/inhalation cycle going on. It ends up carrying a lot of oil out of the motor.

So whatever you do for a vent, it should have a check valve. That massively, massively reduces the exhalation/inhalation you otherwise get from the variable volume crankcase. If you've got a check valve on each vent, all you get is a small net outflow equal to the blow by. The head breather holes are plenty big enough for this small net outflow, all you need to do is reroute them out of the intake tract. The pieces to do this are readily available in the aftermarket.

The factory umbrella valves are very effective at eliminating the exhalation/inhalation cycle, last a pretty long time, and are simple to change when they finally go bad.

I've played with crankcase venting to death, attempting to measure some change on the dyno sheet, and have largely failed in that effort. The only thing I've been able to establish that truly affects the dyno sheet is to remove the blow by from the intake tract. That gives a small but significant gain over a wide rpm range.



Nothing else I tried, including breathing off the timing plug hole, made any measurable difference. My advice is "don't try to solve problems you don't have".
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  #29  
Old 29th December 2015
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Wish this site had a like button to press for this^ post!
Joe
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  #30  
Old 29th December 2015
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way interesting hammer. I can understand a high oil content in the vapors but from what I see is mostly water unless the engine is toast. I wonder why it shows on the dyno? on my 440, I used holley water injection system and it was a definitely a plus, but it was a controlled system. any ideas?
as a side note, I have seen commercial inductions so gummed up with blow-by residue it had to effect it.
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