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Engine Mechanical TopicsDiscussion for motor builds, cams, head work, stripped bolts and other engine related issues. The good and the bad. If it goes round and around or up and down, post it here.
That's what I'm trying to figure out. Might explain the need to keep the head breathers.
When my stock head breathers started sucking air in on upstroke my rocker cover rubber was violently, repeatedly blown out and my head gaskets weeped on the dyno. They build the most at idle and just above and then from about 4500rpm on which is why they wet sump during sustained 4500+rpm. And why my head gaskets weeped on the dyno then quit.
we had a couple guys build slack tube testers to determine how these motors behaved when it comes to crankcase pressure and venting. Hammer tested numerous configurations as well. As far as power goes the only thing that made a difference was getting it out of the intake. That consistently added 2-3 ponies across the entire rpm range.
The krankvent is just a better one way valve than the stock umbrellas. Easy access, easy cleaning if necessary. And not prone to failure. It maintains a constant slight vacuum under the pistons so they aren't fighting pressure on downstroke.
Last edited by 60Gunner; Jul 29, 2020 at 02:10 PM.
Someone please enlighten me. Why is venting via head breathes to the atmosphere inadequate and requires a second venting system. I run two performance motors and venting to the atmosphere via the head breathers has always worked without any issues whatsoever.
Someone please enlighten me. Why is venting via head breathes to the atmosphere inadequate and requires a second venting system. I run two performance motors and venting to the atmosphere via the head breathers has always worked without any issues whatsoever.
Til they fail. And they do. I've seen the plastic housing warp from the heat of the heads. The umbrellas don't seal on upstroke anymore. I've seen them fail in 10,000 miles. Mine did in 29,000. When they do, it can be a real problem. Now you're pulling the rocker boxes. Sometimes heads. Just to change the damn breathers. Not to mention a much cleaner look without them but you can still vent from the heads with the krankvent externally if you want and keep or remove the stock ones.
We replace a lot of things "that work" for a lot less.
I don't see the need for venting out of more than 1 location tho.
But I'm still trying to wrap my head around sucking more air in.
I did this before I moved it to the cam chest. I could feel the difference right away because my stock ones were bad. Even if they're iffy you can tell.
I'd be willing to bet a lot of chronic top end leaks are because of the stock breathers.
Last edited by 60Gunner; Jul 29, 2020 at 06:30 PM.
Sorry, here's a link to the Hayden Krankvent.
I don't buy into the 2-8% increase in hp but my experience and a lot of others was a freer revving motor and no more oil leaks.
Last edited by 60Gunner; Jul 29, 2020 at 07:00 PM.
Don't believe two vents are necessary; overkill IMHO. Both my bikes, '02 and '05 make plenty of HP/TQ and relatively high compression. Head breathers were replaced with the later stamped units and each vented through a crank vent to a small vented catch can filled with a fibrous material to catch the oil mist. Never an oil puke, never a drop from the small catch can. Picture attached and the catch can is visible but the picture may have to be enlarged to see it clearly just below the air filter. The air filter has since been changed to the SE Heavy Breather with the same vent setup. Works great and I see no reason for a second venting system.
I normally would agree w djl and for medium size builds I still agree. But from all the builds I’ve done, redone, repaired, the larger ci combined w compression more importantly ccp north of 205, in hot temp riding conditions along with certain riding habits, the tank vent addition has made a notable improvement. Rocker gaskets, base less stressed, less pressure out the head breathers. There are ways you can tell when your bike is less stressed and I’ve noticed just that.
I've always said the stock breathers are adequate at best. Maybe fine for a stock motor.
I'm betting if you tried the krankvent you might just not need a second vent. I know it's hard to swallow at $125. I was skeptical too but pleasantly surprised. I'm not kudding. I could tell at startup. It ran better and sounded better right away.
Now maybe the newer twin cam breathers are a little better but it's still a worthwhile breather mod either way you do it. Buy one and just stick it on after the T in your hoses. It would be best to pull the stock ones thobut you don't have to. Just leave the oil pads in.
Not having anything hanging from the heads is a bonus if you run it out of the cam chest. There's quite a few in the evo world that believe that's where the crankcase should be vented anyway.
Last edited by 60Gunner; Jul 29, 2020 at 10:21 PM.
Sticking with my head breather setup in the 98" which is not a big motor but does run CCP at 212psi and the head breather setup is working fine and there are two crank vents with one way valves. Someday, I will probably build a "big" motor to replace the 98" and I will consider a second vent then but for now, if it ain't broke,,,,,,,,,,,,,,,,,.
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