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-   -   Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (http://xlforum.net/forums/showthread.php?t=2073932)

bustert 22nd July 2019 21:37

there are cheap digital pressure recorders out there.
with the right orifice, a water manometer could be used, they use this methods on diesels to determine blowby and engine wear.
i do not think the hd engine achieves a negative pressure.
even if you tested this in alabama, it will not hold true every where. the elevation and barometric will have its nasty hand into the pie.
in a recip aircraft, the breathers pretty much remain an open system..
the little mention of auto pcv is not a very good idea for at least 3 reasons.
i have a couple of slack tubes and if i get time, i will do a garage test. this also is moot since everything changes with throttle opening.

Hippysmack 23rd July 2019 00:08

If you think about it without a negative pressure on upstroke, even if slight, the umbrella will not close.
It's not a seal from atmosphere without suction on the inside.
I can see negative building as the piston rises since the positive went out the vent.
Too much ring gap could alter that though.
Some pressure escaping the rings on upstroke to sort of equalize somewhat I'd buy.

I agree if tested here, the results won't be the same everywhere depending on elevation.
But that may be able to be calculated out later?

I tried again today with the cap.
Oil temp 210, raised idle to 1200 and lost 700 RPM.
So it's a variable figure.
I got the same figure when just cracking the cap open as with full off.

edit:
I forgot to mention I pulled the cap just after the idle was sufficient to take the enrichment knob back in.
Absolutely no affect on RPM.
So there is a correlation to the heat of the oil. ;)

dieselvette 23rd July 2019 02:36

Quote:

Originally Posted by bustert (Post 5764347)
there are cheap digital pressure recorders out there.
with the right orifice, a water manometer could be used, they use this methods on diesels to determine blowby and engine wear.

Just hook up a balance tube to the back of your a/c, and fire it up, rev to full RPM and you will see how restrictive your a/c filter is at full flow. Compare that to the crankcase pressure variations and see that this is of little significance. If your a/c is significantly restrictive, get a new filter.

Yes things drop out of vapor or coalesce with pressure/flow changes, but I think that once anything is past the umbrella valve it doesn't matter anymore whether it presents itself as droplets or vapor, there's very little of anything unless you have parts somewhere in the engine not working right.

You are correct that a/c design matters for flow & HP, but only at higher RPM (flowrate). And then the only filter determines pressure drop, not the backplate design. Backplate design affects how "smoothly" the air enters the carb.

bustert 23rd July 2019 15:04

first of all, do not need to do that, all i have to do is hook up my scan tool to the honda and pull the air cleaner off and watch short term fuel trends, THEY WILL CHANGE!
second of all, how does a filter work??? by impactation right???
if that is true, there has to be a resistance to flow and the media is like a labyrinth maze.
offshore, air intake is part of a preventive maintenance and was monitored via electronics and you could see the results and varied by rpm and load. when filters cost several hundred dollars, trust me, the oil company wants their money's worth. same with oil, at 70>80 dollars a pop and you have 7 large or 21 small units, it adds up so they monitor diff'l and run oil analysis and with the addition of spinners, they go well over a year on an oil change 24/7 run time.
i think we are on diff tangents.

Tomcatt 24th July 2019 00:25

Quote:

Originally Posted by Hippysmack (Post 5764036)
When I first pulled the cap, the engine almost died.
After firing back up and pulling the cap, it stumbled but ran rough on 950 RPM.
It was an instantaneous response to pulling the cap.

I tried this today after getting home from a ride. '17 1200C so it's EFI. Bike was sitting idling on the side stand, 310F rear cyl head temp.
Cap removed or in place made NO difference. RPM didn't change. I've got Power Vision hooked up and monitored IAC steps, MAP, RPM, Timing. Nothing changed. ECU made no changes to compensate. Oil level is at the low end of the dipstick.
Just FWIW.

60Gunner 24th July 2019 00:39

Quote:

Originally Posted by Tomcatt (Post 5764626)
I tried this today after getting home from a ride. '17 1200C so it's EFI. Bike was sitting idling on the side stand, 310F rear cyl head temp.
Cap removed or in place made NO difference. RPM didn't change. I've got Power Vision hooked up and monitored IAC steps, MAP, RPM, Timing. Nothing changed. ECU made no changes to compensate. Oil level is at the low end of the dipstick.
Just FWIW.

I pulled mine this morning idling. I didn't notice any change either.

Hippysmack 24th July 2019 01:08

Quote:

Originally Posted by Tomcatt (Post 5764626)
I tried this today after getting home from a ride. '17 1200C so it's EFI. Bike was sitting idling on the side stand, 310F rear cyl head temp.
Cap removed or in place made NO difference. RPM didn't change. I've got Power Vision hooked up and monitored IAC steps, MAP, RPM, Timing. Nothing changed. ECU made no changes to compensate. Oil level is at the low end of the dipstick.
Just FWIW.


Quote:

Originally Posted by 60Gunner (Post 5764631)
I pulled mine this morning idling. I didn't notice any change either.

Very interesting.
Both rubbermounts.

Neither with the slight atmosphere drainback in the breather system.
As in 91-03 rockerboxes.

Quote:

Originally Posted by bustert (Post 5764097)
the first run was at 130*f oil temp and the engine did drop 100 rpm after a few seconds.
on the return, the roads were drier, have to be careful as she'll break traction. i was able to get temps a tad over 140*f and the rpm drop was more pronounced but did not die.

decman has a rigid S model, not sure about cantolina.

hhhhhhmmmmm.
That tiny hole on the back side of the umbrella will suck atmosphere back from the head vents into the engine on upstroke......
It's suppose to drain any oil that gets past the umbrella into that little cupped area.
http://sportsterpedia.com/lib/exe/fe...hippysmack.jpg

I see the 04 Up breather assembly doesn't have that tiny hole.....
What if one was drilled into the shelf underneath the middle of the 04 Up plastic housing?
Even though 91-03s don't have the estrained issues as the rubbermounts, they do better with CC pressure including that tiny hole.

Hippysmack 24th July 2019 01:27

Anybody else have a rigid mount that lowers the RPM when the oil cap's pulled on hot idle?
I wouldn't think this has to do with compression ratio unless there is more normal blowby in an S model than others.
What about 86-90 and prior models?

60Gunner 24th July 2019 01:34

Not sure If matters, I doubt it, but I'm not breathing from the heads anymore either. Never tried it with the failing umbrellas.

Hippysmack 24th July 2019 01:47

Yeah I probably shouldn't have assumed but I did assume your Krankvent wouldn't allow back-fed air.
Seems like the advertisement you posted said it was a dedicated one way valve, shutting down air intake when closed.


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