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Vegas Vulcan
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1,161 Posts
Discussion Starter · #1 ·
Was getting way too much oil in the airbox (not stock, a caddman variation) so I rerouted the oil breather tube to a separate crankcase filter and mounted it high on the frame above the choke knob.

There was so much oil that it was getting into the throttle body and causing the motor to stumble badly on acceleration. I've run about 100 miles with this setup and it seems to work fine now, no oil on the crankcase filter.

I was wondering why I was getting what I assume to be ring blow-by. Holding a lighter to the adjacent to the filter it draws the flame towards it on idle but the flame becomes neutral when revving so I don't think blow-by was the problem.

I did a compression check for the first time, 32,000 miles on the bike and found it to be within specifications which are 110 to 185 lbs. psi however the front jug is at 150 lbs and the rear is about 125. I was wondering if anyone has this variance in the compression from front to rear and if it's considered normal.

The bike is running much better now that the crankcase has it's own breather.
 

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I've seen worse, but typically you do not want to see more than 10% variance between the cylinders so 15 psi is the max in this case for a healthy engine if the test was performed properly. Was the engine warm at the time of the test? Did you take steps to ensure no valves were sticking?
 

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Vegas Vulcan
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1,161 Posts
Discussion Starter · #4 ·
I wouldn't worry about it. They're high enough and the compression releases make accurate, "real" reads difficult.

How high in the "window" do you keep your oil level?
I was considering starting the motor with just one jug firing to accurately test the other so as to get past the compression release system but wasn't sure how safe that was for the engine. I guess it wouldn't hurt for just a short period, especially since Harley does it to keep their engines cooler under extreme heat conditions..

I usually fill to the top line and may have overfilled the last time accounting for the excessive oil in the box but even when I'm right in the middle between the lines I still get oil in the box to a fair degree, enough that it is being sucked into the throttle body.

I used some cleaner to spray into the fuel injection system and the bike runs much better, actually great. My concern was that the oil being sucked in might have scored the cylinder walls and pistons.
 

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Vegas Vulcan
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1,161 Posts
Discussion Starter · #5 ·
I've seen worse, but typically you do not want to see more than 10% variance between the cylinders so 15 psi is the max in this case for a healthy engine if the test was performed properly. Was the engine warm at the time of the test? Did you take steps to ensure no valves were sticking?
Engine was warm. Not sure how to ensure a valve isn't sticking.
 

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Nobody Home
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1,768 Posts
The oil may leave some carbon but that will usually burn itself out. You can check one cylinder at a time with it idling. The specs are for cranking speed, throttle held open (which they usually don't mention) so your results may not match spec but you can see how close the cylinders are to each other. Make sure you disconnect and ground the plug wires (both plug wires) for the cylinder you're testing.

Did you hold the throttle open and have the plug out of the other cylinder also when you did your initial test?
 

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Vegas Vulcan
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1,161 Posts
Discussion Starter · #7 ·
The oil may leave some carbon but that will usually burn itself out. You can check one cylinder at a time with it idling. The specs are for cranking speed, throttle held open (which they usually don't mention) so your results may not match spec but you can see how close the cylinders are to each other. Make sure you disconnect and ground the plug wires (both plug wires) for the cylinder you're testing.

Did you hold the throttle open and have the plug out of the other cylinder also when you did your initial test?
Crap! I missed that part about removing the plugs from the other cylinder and upon checking the manual again there it is in black and white.
  • Remove both spark plugs from the other cylinder
Oh well. I'll redo it. I wonder how and why it would affect the outcome? I did hold the throttle open though and disconnected the wires from all the remaining plugs.
 

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Nobody Home
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You're trying to remove variables. The cranking pressures you measure will be, to an extent, dependent on cranking rpm. I'm not convinced pulling BOTH plugs out of the "other" cylinder is necessary but I'd sure pull one. Ground the plug wires. This is a good precaution. If you don't the sparks have to go somewhere, like thru the insulation in the coil.
 

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Vegas Vulcan
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1,161 Posts
Discussion Starter · #11 ·
Well 2 weeks of the external crankcase filter and I cannot stand it anymore. The fumes are awful, especially with the windshield. Even my friend riding on his bike behind me can smell it. Says it smells like his CB750 with the K&N setup. He also has an external filter. Strange thing is that I was getting tons of oil in the airbox but virtually none in the external crankcase filter. I'm wondering if there is a problem with the intake actually sucking oil up through the crankcase vent hose.

When I did Chucksters plate mod I went with a smaller filter with just 1.75" height. Perhaps it's not providing enough space in there. I've ordered a 2.25" height filter to see if this will help.
 

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Vegas Vulcan
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1,161 Posts
Discussion Starter · #13 ·
Update

If you remember I was getting tons of oil in the air box and even went to using an outside breather filter. Let me tell you, the smell from the crankcase is some nasty stuff. So I made a few changes and rode this weekend for about 150 miles with some very hard riding through the mountains. NO oil in the airbox. Not a drop.

What I did to correct this was switch to a taller filter, from a 1.75" height (K&N E-4655 with 1" width of breathable element) to a 2.25" height (K&N E-4665 which gives me 1.75" width of breathable element).

I have some arguing against this but I believe the small filter was just not enough air, clogging faster and causing the bike to actually suck air from the breather hose. Of course my one time overfill might have damaged the breathing properties of the original filter since even after I cleaned it I could not get back the original light color of the filter where the motor oil had stained it.

Also the bike is running much better with stronger pull, a testament to the easier breathing. Needless to say, I'm happy again.
 
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