Board index Flathead Power-Technical Questions, Answers, and Suggestions K-Models Breathing on the KH

Breathing on the KH

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Post Wed Jul 26, 2006 11:40 pm

Posts: 240
Location: Kirkland, WA, USA

Breathing on the KH

I know how the KH is suposed to get the crank case pressure out by sending it along with the oil, up the breather tower. Where does new air come in from? They have no primary side breather, and it has to come from somewhere? If it does not, it might explain all the problems I have with rings.

Best regards,
Barry55KH

Post Thu Jul 27, 2006 3:26 pm
xlr

Posts: 149
Location: calif
hi what problem areu having with rings? on your cam cover you have a breather. most of the time if oil is coming out of breather your rings are bad. to much crankcase pressure.

Post Thu Jul 27, 2006 7:57 pm

Posts: 240
Location: Kirkland, WA, USA

I am looking for where the air goes into the crank case? I know where it comes out. It has to come from some where. Thanks for your ideas.

Barry55KH

Post Fri Jul 28, 2006 5:32 am

Posts: 330
Location: north central Ma.
Barry.
I far as I can tell it's all blow by air and the changing crank case volume due to piston rise and fall. If rings are well sealed air will go both ways from the breather.

However I'm far from an HD dry stump guro. All my dry stump work has been with 4cyl race cars where the scavange pump pulls 28 inch of vacum in the motor with lite thention rings

44dwarf
"Smok'in the competition NOT Tobacco"
"Transplant organs, Don't bury them!"
Why dwarf? 5/8 scale race cars! http://www.dwarfcarracing.com

Post Fri Jul 28, 2006 9:02 am

Posts: 240
Location: Kirkland, WA, USA

I got the same expaination from Hans, well almost. Thanks 44Dwarf, that makes it a lot clearer.

Hans said, "Barry, the breather has several functions. First one is to keep the
pressure in
the crankcase low. Otherwise if both pistons are down, you would have
say 2 atmosphere
pressure in the case. This could possibly break the cases and might
blow oil thru
seals. What you need for this, is a breather that opens momentarily
when both pistons
are close to the lowest position.
If you are at idle, the situation is close to this.

When you open the throttle, some gas will start leaking past the
pistons. This is
sometimes called blow-by. This gas has to get out thru the breather.
This now requires
a sizeable opening but still much smaller that the HD size, and that
opening has to
remain open long enough. Timing is still basically as above, but you
advance the
timing a few degrees since gasses always lag a bit with respect to
the mechanical
movements." (Per Hans.)

Thank you all!

Best Regards,
Barry55KH

Post Tue Aug 08, 2006 5:03 pm

Posts: 51
Location: felton,Ca.USA
On our KR race motor I blocked off the stock breather and installed a 5/8" breather on the timing cover with a baffle. At the end of the breather hose I have one way check valve that only lets air exit the crancase. While I have no way of measuring the crankcase vacumn or pressure,
I suspect its negative because the minor oil weepage around the lifter gaskets dried up. The point is, as Dwarf stated, you want as high a vacumn as possible.
Mike

Post Wed Aug 09, 2006 7:09 pm

Posts: 919
Location: RENO,NV. U.S.A.
If you're talking about the breather tower on the pump.I fail to see how that would work on an everyday street bike,on a high rpm race ebgine possibly. On an average engine it would wet sump and cause more problems than it's worth.

Post Wed Aug 09, 2006 8:47 pm

Posts: 51
Location: felton,Ca.USA
BREWSKI wrote:
If you're talking about the breather tower on the pump.I fail to see how that would work on an everyday street bike,on a high rpm race ebgine possibly. On an average engine it would wet sump and cause more problems than it's worth.


I'm talking about the blocking off the breather at the front of the timing cover. The timed tower breather remains. What the check valve does is reduce the pumping action and related losses. This would be benificial on any motor.
The Ducati twins use this system without the timed breather.

Post Thu Aug 10, 2006 12:00 am

Posts: 630
Location: belgium
That's how Harley did the sportsters in '77, they had a one-way valve at the breather on the cover.
I don't have a partsmanual for the sportster at hand, so can't give a #.
Stéph

Post Fri Aug 11, 2006 3:58 pm

Posts: 919
Location: RENO,NV. U.S.A.
Thanks for the info,wasn't aware that H-D actually did that on the later XL's. BREWSKI

Post Sun Aug 13, 2006 3:27 pm
panic

Crankcase vacuum is satisfied by air flowing back through the open breather slots for about 50 to 60 degrees after BDC.
Higher RPM: longer delay, XR750 is open for 90 degrees.
Higher case vacuum = more pumping loss.

Post Mon Aug 14, 2006 8:02 pm

Posts: 51
Location: felton,Ca.USA
panic wrote:
Crankcase vacuum is satisfied by air flowing back through the open breather slots for about 50 to 60 degrees after BDC.
Higher RPM: longer delay, XR750 is open for 90 degrees.
Higher case vacuum = more pumping loss.



Higher case vacuum = more pumping loss.
Panic
Are you speaking of a loss of pumping or a loss of power from pumping?
Mike

Post Fri Aug 25, 2006 8:44 pm

Posts: 763
Location: Pa. , USA
Hey Mike, I was thinking about doing that, what brand check valve did you use ? part# ? thanks, Tim
Vintage roadracing, Class C, AHRMA # 335

Post Sat Aug 26, 2006 1:18 pm

Posts: 51
Location: felton,Ca.USA
Tim 435 wrote:
Hey Mike, I was thinking about doing that, what brand check valve did you use ? part# ? thanks, Tim


Standard #AV30, Borg Warner #CV-39, Auto Zone-Sorensen #779-2945.
I use it with a small K&N on the outlet side. I use the BW brand.
Mike

Post Sat Aug 26, 2006 8:39 pm

Posts: 763
Location: Pa. , USA
Thanks Mike, if it works out I want to attach one to the exit side of my catchbottle/breather..
Vintage roadracing, Class C, AHRMA # 335

Post Sun Aug 27, 2006 7:30 am
panic

One of these days I'm going to make a strobe photo of a check valve at 5000 RPM.
You know, about 3000 RPM after it stopped working, and is stalled partially open doing nothing?

Post Sun Aug 27, 2006 1:45 pm

Posts: 51
Location: felton,Ca.USA
Tim 435 wrote:
Thanks Mike, if it works out I want to attach one to the exit side of my catchbottle/breather..

Tim
Just remember its important that the crancase be completely sealed in order for the check valve to work correctly. I sealed of the primary and trans via a crank seal and plugged the crancase to primary check valve.. I vent the trans and primary thru a hole drilled in the top screw in the primary inspection cover. Also I vent the oil tank to atmosphere thru a foam filter. And don't forget to have the breather timed correctly.
mike

Post Sun Aug 27, 2006 2:06 pm

Posts: 51
Location: felton,Ca.USA
panic wrote:
One of these days I'm going to make a strobe photo of a check valve at 5000 RPM.
You know, about 3000 RPM after it stopped working, and is stalled partially open doing nothing?


Panic
You may have a point with some of the ball type check valves if thats what you are refering to. What I'm talking about is a reed type that has very little mass and spring pressure to help close it. We are not talking about a very strong vacumm here,probably just a few inches of water. I don't think it would make any power difference but it calms the turbulence in the crankcase and helps with scavanging. A check valve would only show a power gain from better scavanging if the engine was prone to sumping, which would cause a power loss because of drag on the flywheels.When I drain the crancase after a race I only get 1 to 1 1/2 ounces of oil. And like I stated in a previous post it dried up the minor oil seepage around the lifter blocks which is an indication of a pressure change in the negative direction.

Post Thu Sep 21, 2006 6:00 pm

Posts: 1668
Location: Interlaken, NY USA

Maybe the reeds would be more efficient than balls at higher rpms. I know the BSA Goldstar went from the ball type of the M20 to a timed breather to keep crankcase pressures down, this was back in the mid '50's. I've lived it, the ball type wouldn't handle high rpms. Gives me a chuckle when these evo guys add them to their breathers.
Dr. Dick


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