too much pressure in the crank case... - TwoWheelForum: Motorcycle and Sportbike forums
 
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post #1 of 19 (permalink) Old 09-06-2006, 07:22 AM Thread Starter
 
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too much pressure in the crank case...

hi all.. i need to figure out a peculiar problem with my ZL900..(basically the same engine as a gpz900 with couple of differences)


anyway.. while under load(generally at a higher RPM) oil pushes through the oil seperator and spews out the airbox.. alot..

so... the seperator isnt bad, in fact its now new 'cause i thought sure that was it..

what builds up that much pressure? bad rings?.. oil pump malfunction?
no smoke.. oil is clear..

??
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post #2 of 19 (permalink) Old 09-06-2006, 07:23 AM
 
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Too much oil perhaps.



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post #3 of 19 (permalink) Old 09-06-2006, 07:40 AM
 
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clogged oil filter inlet?

Last edited by bumblebee; 09-06-2006 at 07:43 AM.
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post #4 of 19 (permalink) Old 09-06-2006, 11:14 AM
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Quote:
Originally Posted by bumblebee View Post
clogged oil filter inlet?
Either that or just design...

Could plumb it to the road...




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post #5 of 19 (permalink) Old 09-06-2006, 11:57 AM Thread Starter
 
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Quote:
Originally Posted by marko138 View Post
Too much oil perhaps.


lol.. not that simple im afraid.. but thanks for the suggestion..
to be sure though, i drained all the oil and only replaced 2 qts.. still the same phenomenon..


Quote:
Originally Posted by bumblebee View Post
clogged oil filter inlet?


checked that.. it was my first best guess after a bad separator..

Quote:
Originally Posted by Gas Man View Post
Either that or just design...

Could plumb it to the road...


"plumb it to the road".. help me there, i dont understand..

as to design.. the oil seperator/reservior makes no sense.. the porous cast filter obstructs nothing.. in fact the path that the oil/oil vapor takes has no obstruction by design..
IMO, the vent to the airbox is breaking out of the wrong side of the reservior, (or the separator filter plate is designed onto the wrong side of the reservior) and doesnt even utilize the cast filter..


anyway.. back to the crankcase pressure issue..
ive been doing some more research and have read that rings are the most likely suspect in a high compression motor..
the articles mostly referenced large bore v-twins, or high compression single cylinder motors(quads)..

i cant find an easy way to determine that as a fact until i pull the top end.. i suppose compression testing could find a "lazy" cylinder, so ill start there.

ill keep adding as i find more, but suggestions are certainly welcome..
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post #6 of 19 (permalink) Old 09-06-2006, 12:09 PM
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ok... well on the large v-twin motors. There is a reid valve on the bottom side of the motor that is slotted 50% open 50% closed... think of your kitchen spicies... (minus the holes section) turn the top and its open, turn it again and its closed.

Well this vlv will sometimes get stuck open... causing excessive amount of oil spewing. Not sure if your setup is similar or not...

On my large v-twin... the hose you speak of is plumbed from the factory to the carb. What I did was pull that hose from the carb...plug that hole. Then run the hose to the ground behind the tranny.

The important thing to figure out is this...

Is the motor spewing out a excessive amount or is the amount normal and you're just riding it that hard. The large v-twins only do this when you ride them hard..




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post #7 of 19 (permalink) Old 09-06-2006, 12:34 PM Thread Starter
 
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if i hold the throttle to about 3 to 4g's, itll throw out a qt. in about 1min..
i dont think thats per design..

many of the articles i read was using the v-twins as a reference because of the size of the piston naturally making it more succeptable for leaking compression..(not so true with modern machining though..)

for example: http://www.motorcyclecruiser.com/tec...cycle_engines/

and:
http://groups.google.com/group/uk.re...978eea165c2703

im certainly not making the assumption its a problem with rings, but its another place to look..
truthfully, the engine appears to have been sitting for a while regardless of the previous owners "smoke and mirrors" speech..
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post #8 of 19 (permalink) Old 09-06-2006, 12:37 PM
 
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check for piston ring leakage. combustion blowby will increase crankcase pressure. I can't remember if valve seal leakage will do the same. use a simple compression test or pressure leakage test for better accuracy.


-a|ex

Last edited by Back _Marker; 09-06-2006 at 01:09 PM.
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post #9 of 19 (permalink) Old 09-06-2006, 12:46 PM
 
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Quote:
Originally Posted by Gas Man View Post
...What I did was pull that hose from the carb...plug that hole. Then run the hose to the ground behind the tranny...
How unsophisticated. My Honda is much more modern. It has the same crankcase breather hose leading to the ground, but it is capped. The owner's manual recommends regular draining and "Service more frequently when ridden in the rain, at full throttle, or after the motorcycle is washed or overturned." Overturned???

As for the Eliminator, excess blowby on cars is usually a clogged PCV valve or bad rings.
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post #10 of 19 (permalink) Old 09-06-2006, 01:07 PM
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Yeah that doesn't sound right Demise.

NW... yeah I know.... the v-twin world is old school low tech...




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post #11 of 19 (permalink) Old 09-06-2006, 01:23 PM
 
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But a ring issue or blowby would leave a smoke or smell trail... And if it was a "too much pump" issue...the oil would froth or cloud, right?
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post #12 of 19 (permalink) Old 09-06-2006, 04:58 PM
 
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If its similar to a GPz 900 motor, look at the breather reeds on the top of the motor, they're likely stuck open letting oil OUT, when they should be closed. either that, or they're in upside down.
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post #13 of 19 (permalink) Old 09-06-2006, 05:54 PM
 
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Quote:
Originally Posted by bumblebee View Post
But a ring issue or blowby would leave a smoke or smell trail... And if it was a "too much pump" issue...the oil would froth or cloud, right?
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post #14 of 19 (permalink) Old 09-06-2006, 07:32 PM Thread Starter
 
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all good stuff..

ill look for "frothing" or some discrepancy in the oil.. what comes out sure looks clear.. some bubbles are expected considering the path its taking.. not foamy though.
i should be able to check the oil pump without digging too deep..

im thinking that its over pressurizing during a downstroke on one or more of the cylinders.. it should show the loss of pressure in the cylinder with a compression check.. i need to set the valves first..
no smoke though..

i didnt notice them, but ill look for those reeds.. are you implying that oil would be coming from/through the reeds themselves?
or if theyre stuck and not opening its holding too much pressure?

i saw a single relief valve in an exploded view in a suppliment, i need to check that along with compression next..
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post #15 of 19 (permalink) Old 09-06-2006, 11:41 PM
 
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The reeds I'm talking about, are situated in the valve cover, in the image below, part numbers 12021 are the reeds you need. this is an image from an 87 ZL900A2, which is very similar to the GPZ900A2.
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post #16 of 19 (permalink) Old 09-07-2006, 07:15 AM Thread Starter
 
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thanks King Bob.. yep, i saw those.. ill check them..
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post #17 of 19 (permalink) Old 09-07-2006, 07:44 AM
 
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Holy Schematics! Great find on the diagram! Rep points...
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post #18 of 19 (permalink) Old 09-08-2006, 04:47 PM
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Quote:
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Holy Schematics! Great find on the diagram! Rep points...





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post #19 of 19 (permalink) Old 09-10-2006, 03:20 PM
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Holy Schematics! Great find on the diagram! Rep points...

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