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-   -   Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (

dieselvette 26th July 2019 06:53


Originally Posted by 60Gunner (Post 5765018)
Besides being just barely adequate, they're in the worst possible location. But even if you didn't want to to do the cam cover mod, the krankvent in the existing breather hose off the heads is still better. I tried it there first.

I'm not going to claim that the stock breather valves are always good enough, but I do think location is worth consideration. Inside the head - probably not ideal, but wouldn't it have been easier for HD to hide it behind the cam chest (at oil tank vent port) and use only one?

Venting from the cam chest - there is condensation - any concern with lack of air movement through the valve covers, causing moisture to have no way out? The most likely place for vapor to condensate is on the inside of the valve covers, being the coolest on startup and cooldown.

HD put breathers on both heads, not just one. Why? And I don't understand fully what happens if exhaust valve seals leak either, or where those gasses would go or where you want them to go.

So I'm not sold on capping the head breather holes, but I'm not saying it's a horrible idea either.

In my line of work we deal with check valves (leaking) all the time. If it has higher crack pressure, it will seal better, but also it holds back more pressure. Not sure if that's what you're describing with the Crankvent, but perhaps your CC is running a tiny bit higher pressure than stock, due to the heavier check valve? Obviously if it works better, you should stick with it.


Originally Posted by Hippysmack (Post 5765047)
Wet sumping and crankcase pressure are two different conditions.
Better scavenging of sump oil = less aeration = less froth

Definitely a factor. When the scavenging port going UP out of the crankcase is primed full of good oil, the pump will work perfectly, even without the extra push. It's when there is air in the oil (even microbubbles) then it *may* loose prime and the only chance of recovery is a push from the downstroke. Then it's a downward spiral...


Originally Posted by Hippysmack (Post 5765047)
I believe it to be the speed of the valve closing that either helps or hinders the time frame that vacuum is able to build.
So the Hayden, affixed to close faster as mentioned previously, simply allows what vacuum the individual engine can make to build faster.

Not entirely - if it closes faster, that also means it was harder to open in the first place. Perhaps the key is simply that it actually seals properly, when it does close.

dieselvette 26th July 2019 07:04

Watched the video - thanks for posting the link. Betting the sporty has a tiny tiny air leak somewhere that's just enough to bleed off the blowby.

But if you can be 100% certain your system has no air leaks, perhaps that is a valid way to test for blowby? No - because there's no way you can be 100% certain, so it is subjective.

60Gunner 26th July 2019 09:42

Venting from the oil tank vent line, which vents to the cam chest btw, was tried. Bad idea. Oil went with it.
What I'm describing with the krankvent is I'm running LESS, more like no, pressure. Not more. You're running higher pressure, not a good thing, because the stock umbrellas let air back in before closing. Alot more when they fail. This is where poor sealing check valves are a problem. Not the other way around. If your check valve is holding back pressure from escaping you have it in backwards!
The Krankvent closes immediately at the first sign of air being sucked back IN. Hence no pressure being added and it releases pressure from the pistons going down immediately it doesn't take more pressure to open it because it seals better from the other direction!
Why would leaky exhaust guide seals matter where the crankcase is vented?
Venting from the heads and the cam chest was also tried. Not a good idea. One for the other or you'll have scavenging issues. If you move it to camchest the head breathers get blocked. Period.
As for why it was moved to the heads is so it could be recirculated thru the intake because of EPA regs saying it has to be would be my guess. Also a bad idea which is why most are venting to atmosphere anyway. Mixing that nasty crap in your combustion chamber leaves nasty carbon deposits in there and on top of your pistons. Before that it was being vented exactly where I am now. In the cam chest.

Four Speed 26th July 2019 09:57

Yes that covers most of it. I also think the wave pulses will be stronger closer to the pistons than up in head which should help an effective
valve vent the pulses better. But in expressing this preference we risk being accused of bashing head breathers to make people change............:doh
I tend to think that people make up their own minds :)

60Gunner 26th July 2019 10:30

Well in his haste to justify keeping the stock breathers, to himself by the sounds of another post where he says he'll probably regret it, I think he is mistaking a check valve for a pressure relief valve. 2 totally different things. A better check valve keeps little to no air from being sucked backed in. It doesn't hinder or improve pressure escaping. Except that there's less to escape when it's not allowed back in.
A pressure relief valve takes a certain amount of pressure to open and release pressure. Not a check valve.
The only justification he has isn't whether the Krankvent or venting from the cam chest is worse than the stock head breathers but whether or not it's that much or any better.
I can't even speculate what the exhaust guide seals thing is about.

60Gunner 26th July 2019 15:10

Here's a good read on breather systems.
I'm going to copy that upward design, use some bigger thin walled clear tubing to observe, and put a filter on the outlet of the krankvent like this since it will be pointing up. My guess is all oil will drain back.
Only problem is the front exhaust head pipe in the way. I might have to settle for going up at 45° to the down tube on the left side then straight up.

Four Speed 26th July 2019 16:10

Upward should work fine but definitely keep the valve away from the exhaust heat. The Mk1 Evo has the hose outlet at about 10 O'clock
and from there it ran to the carb back plate so all uphill. Oil can run back but in practice I don't see much unless the engine wet-sumped
while stored. The breather hose on mine just loops under the Mikuni and is terminated above the drive chain. I did have a clear hose on
it but it is just black rubber now as nothing eventful seemed to happen.

Hippysmack 26th July 2019 16:14

Man, talk about not seeing the forest for trees. :doh
I've been looking too high.
The swap to head breathers did increase CC pressure in 91.
With the big problem with scavenging, that should have helped some.
Just as in the 04 breather bolt hole, below the lifter blocks was also increased in 91 with the restricted hole size to the (edit: pushrod tubes).
See the drawing below.

60Gunner 26th July 2019 16:19

The krankvent will go on the very end after it's crossed over to the left well away from the exhaust.

Hippysmack 26th July 2019 16:42

Go back to post#10.
From 1979 and up, the breathers were vented into the air cleaner from the factory.
This vent direction change was implemented while the cam chest was the outlet.
Venting to the A/C was a EPA thing but it has nothing to do with where the vents are.

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