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engine breather port plugged, need advice


SJ David

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ok, it seems somewhere between the finished assembled engine and the installation into the frame my crankcase breather port became plugged.

 

I checked it after I assembled the engine and it passed air easily. Now it does not.

 

Does anyone have some suggestions beside tearing the whole bike apart again?

 

Help?

 

David

San Jose, CA

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ok, it seems somewhere between the finished assembled engine and the installation into the frame my crankcase breather port became plugged.

 

I checked it after I assembled the engine and it passed air easily. Now it does not.

 

Does anyone have some suggestions beside tearing the whole bike apart again?

 

Help?

 

 

Afternoon David

 

Check it again as you turn the crankshaft. The crankcase vent is timed.

 

If that doesn't allow venting then suspect that you don't have enough

space between the rear main seals.

 

 

1150%20crankcase%20venting_zpsjund80ef.jpg

Edited by dirtrider
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Thanks for the info dirtrider.

 

can you tell me about where in the timing that the vent should be open?

 

David

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Thanks for the info dirtrider.

 

can you tell me about where in the timing that the vent should be open?

 

Afternoon David

 

Not without looking at a crankshaft & I'm no where my shop for a couple of days.

 

Maybe you can sort of figure it out from this picture. The rear vent slot is at top when it is venting.

 

 

1150%20crankshaft_zpseoxcuacw.jpg

 

Edited by dirtrider
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Thanks dirtrider for the info, I will have to check it but it looks like maybe mid stroke or close to to it. Any way tomorrow I will have to take it to my shop and tear into this mess and see what I can do.

 

Thanks

 

David

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Thanks dirtrider for the info, I will have to check it but it looks like maybe mid stroke or close to to it. Any way tomorrow I will have to take it to my shop and tear into this mess and see what I can do.

 

Thanks

 

 

Evening David

 

Did you get those rear seals seated to the correct depth when you installed them?

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Well I thought I had, but evidently the rear most seal I drove in too far.

 

I pulled my body fairings, lifted the tank up so I could get to my crankcase breather. I took the oil filler cap off and put a long length of rubber hose in the opening and vertically 36 inches high so oil would not spray out and to let the crankcase breath while I ran the engine on the center stand.

 

While the engine was idling I took a portable air tank and pushed 20 psi air back into the vent fitting. The pressure held so the rear most seal must be right over the passage in the crank.

 

So I guess I will order another set of seals and pull the transmission again and replace them, again.

 

Thanks for all the info dirtrider. If you have any more tips for putting the seals in correctly I would deeply appreciate them.

 

David

 

 

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Well I thought I had, but evidently the rear most seal I drove in too far.

 

I pulled my body fairings, lifted the tank up so I could get to my crankcase breather. I took the oil filler cap off and put a long length of rubber hose in the opening and vertically 36 inches high so oil would not spray out and to let the crankcase breath while I ran the engine on the center stand.

 

While the engine was idling I took a portable air tank and pushed 20 psi air back into the vent fitting. The pressure held so the rear most seal must be right over the passage in the crank.

 

So I guess I will order another set of seals and pull the transmission again and replace them, again.

 

Thanks for all the info dirtrider. If you have any more tips for putting the seals in correctly I would deeply appreciate them.

 

 

Morning David

 

I don't know about tips but personally I have a few rules on those seals.

 

Rule #1- Always look/measure where the original seals are installed so you can duplicate those positions (it's too late for you on this one)

 

Rule #2- Always compare removed seal thickness to the ones removed (if you still have the removed original seals do this)

 

Rule #3- (most important) measure where the vent passage is in from the rear then make sure to figure in seal thickness so you don't drive the rear seal in so far as to block the vent passage.

 

Rule #4- after driving the front (first) seal in LOOK CAREFULLY to verify the seal is in far enough to not block the vent passage.

 

Rule #5- after installing both seals blow some air into the vent hose to verify then the vent passage isn't plugged.

 

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Eckhard Grohe

Hello DR.

 

What feature on the engine is doing the timing? The slot on the crank seems to vent into the cavity between the seals and the cavity is continuous from what I can see in the image. Please let me know how this works.

 

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Morning Eckhard

 

It does vent into that very narrow space between the seals but there isn't much room in there for very much venting air flow until the crank notch lines up with the venting hole plus the bottom of the cavity usually contains some oil so effectively they basically vent with the crankcase notch to the top. (if it was just a simple venting into that space between the seals then why machine a complicated notch in the crankshaft when a simple hole would do)

 

360° firing 2 cylinder boxer engines are very difficult to vent properly without spitting a lot of oil into the venting stream due to the drastic crankcase pressure pulses. (both pistons move in together pressurizing the crankcase then they both move out together causing a negative crankcase pressure)

 

Ideally designers like to do most of the venting at mid stroke when the crankcase is part way between the hi pressure & low pressure.

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Clive Liddell

Hi D.R.,

 

Thank you for the cutaway engine and crank illustrations. In addition to your valuable comments it seems to me that the hole in the crankshaft weight would tend to "sling" any oil back into the (running) engine and thereby separate oil and air.

 

 

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Hi D.R.,

 

Thank you for the cutaway engine and crank illustrations. In addition to your valuable comments it seems to me that the hole in the crankshaft weight would tend to "sling" any oil back into the (running) engine and thereby separate oil and air.

 

 

Morning Clive

 

Yes, that is a very big part of the "through crankshaft" venting system.

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Eckhard Grohe

I don't see where the timing happens. I was looking for a window to sweep past an orifice/passage/window and allow the venting of gasses for a certain portion of a crank rotation. Perhaps the section shown doesn't have that feature in the portion that remains.

 

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Eckhard, timing - not sure there is any? The fact that the crankshaft is spinning would try to centrifuge any oil back into the crankcase. BUT it allows pressure differentials to be compensated for.

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