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Discussion Starter · #1 ·
For some reason, my plugs are fouling with oil. My guess is the valve stem seals are leaking. The bike runs fantastic, fast and smooth, but if I shut it off, it won't start again due to fouled plugs. It can only be rings or seals, correct?
 

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Someone will pipe up sooner or later and suggest a leak down test of your cylinders. Definitive way to see where the leak is.
 
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To directly answer the question, yes usually rings or seals allow oil into the combustion chamber. Though, any vacuum to the crankcase can draw oil into the chamber as well, depending on the type of system (doesn't really apply here.)

While a leak down test will be definititve, I'm curious about the amount of leakage. Specifically, since it won't start after running. If sucking/ingesting/leaking oil this bad, you should notice something else, such as blue smoke out of the tail pipe, poor running/single cylinder, driveability complaint, oil burning smell, etc.

In my experience, a non-restart for fouled plugs I would look to a fuel problem, especially if I don't have any other indicators of excessively burning oil.

Just my opinion, hope it helps.
 

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How long after shut down before you try to restart bike? If valve stem seals are the problem, I think that some time would have to pass before enough oil could leak past the seal and down the valve stem into the combustion chamber. If it is rings then oil will only get into the combustion chamber when the engine is cranking.
 

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Someone will pipe up sooner or later and suggest a leak down test of your cylinders. Definitive way to see where the leak is.
While the leak down test will give the OP a more definitive answer (agreed) even just a compression test will give a clue....and so easy to do on these machines

Edit: if using any extensions (e.g. hydraulic line with threaded end to cylinder head) your "absolute" reading may be affected...but you are looking for closely matching values b/ween L&R
 

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Discussion Starter · #6 ·
Thank you for your input, appreciate it.
There is smoke out of the exhaust, worse on the left, but some on the right as well. It doesn't matter how much time past after running, it will not start. When the plugs are taken out to inspect, they are wet, with oil. Cranking it with the plugs out, it sprays an oil mist out of the spark plug holes (worse on the left). As one of you mentioned, this sort of rules out the rings; it must be the valve seals.
I have to say again, while running, it's fantastic! Runs fast and smooth, love riding this bike! I've owned it over ten years, rebuilding it on and off (life got int the way). Since finishing it, I've only put 50 odd miles on it. I'm anxious to put down some more miles…
 

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Discussion Starter · #8 · (Edited)
After buying it in 2012, I completely disassembled it, rebuilt every part, customizing it along the way. It never really was made road-worthy until now. It's been housed in my cool, dark garage in SoCal so I don't think the seals dried up. Just the same, there's oil on my plugs…:cautious:
I hate to remove the jugs if it's not the valve seals. But it's all it can be other than rings, correct?
 

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Is there oil visible in the plug well? If the inner valve cover gasket fails, oil can run into the well, and maybe seep past the plug. Might be grasping at straws.
Does the head need to be removed to replace valve seals, or can it be done with the valves in place?
 

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Discussion Starter · #10 ·
No oil in well, no leaking valve cover gaskets.
To replace valve seals, the heads need to be removed, along with a few of the front motor pieces, including radiator fluid. 🙁
 

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Valve seals can be replaced without removing the heads. One method involves using air pressure in the cylinder to keep the valves in place but I think this method would be more reliable
 

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Even assuming the valve stem seals aren’t sealing at all, it’s highly unlikely that enough oil would be drawn into the combustion chamber to create an oily mist during cranking. Typically valve stem seals are indicated by blue smoke on startup only, which then dissipates after a minute or two.

This sounds like either the rings aren’t sealing (which could just as easily be due to the cylinder being out of round) or there’s a problem with the crankcase breather system that’s causing excessive blow by gases to get sucked into the chamber.

Check for breather problems by inspecting the air filter for being oil soaked (unless you’re utilizing an oil bath air filter, in which case, perhaps it’s been over oiled).

A leak down test will diagnose problems with the cylinder sealing correctly.

Thank you for your input, appreciate it.
There is smoke out of the exhaust, worse on the left, but some on the right as well. It doesn't matter how much time past after running, it will not start. When the plugs are taken out to inspect, they are wet, with oil. Cranking it with the plugs out, it sprays an oil mist out of the spark plug holes (worse on the left). As one of you mentioned, this sort of rules out the rings; it must be the valve seals.
I have to say again, while running, it's fantastic! Runs fast and smooth, love riding this bike! I've owned it over ten years, rebuilding it on and off (life got int the way). Since finishing it, I've only put 50 odd miles on it. I'm anxious to put down some more miles…
 

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ok, so you rebuilt the entire engine? including pulling the pistons?
Did you replace the any piston rings?

Depending on the level of tear down and parts replacing, if it is indeed a ring problem. It could be broken rings when they were installed or at the very least improperly aligned ring gaps.Always install the ring gaps 120 - 180 degrees from each other. See FSM for further details, etc,etc.

I think a compression test and leak down test will be your least expensive next steps. And virtually no labor as well. While still keeping the bike in running condition (sorta). You can get each one for $50 on amazon, make sure they fit your spark plugs threads.
 

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Discussion Starter · #15 · (Edited)
Everything was tore apart, replaced crank bearings, all gaskets, etc. I can't remember if the rings were replaced in all truth. It's a low mileage bike to begin with so I may have just removed and cleaned them. The cylinders were beautiful, no boring needed.
You may be correct, rings may be clocked wrong. leak-down test to follow…
 

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I've never wrenched on a CX500 motor but I've seen this thing run, and although it smells rich, its black smoke (like gas), and not blue smoke (like oil). But the amount of fresh, amber colored oil on the plugs 10 mins after a warm shutdown is impressive.
I really don't think it's going to be rings, you can't have that much blowby and have it not foul the plugs while running, and this bike runs like a top before shut off. As far as vacuum, I can't imagine the residual crankcase pressure or vacuum strong enough to pull oil into the cylinders, and where would it pull from? It would have to be PCV, a strangely bad head gasket, or through the head itself.
It's not over filled with oil, (unless you have the wrong dipstick) so that leaves......
valve guides and valve seals.
I think you would at the very least, need to pull the valve covers and rockers and look at the seals, wiggle the valvestems..... (my 2 cents).

I just thought about this one last simple test to tell if its rings or head. Get the motor nice and hot, then shut down and pull the plugs 10 min after shut down WITHOUT ever cranking the motor. If wet, maybe rings. If dry, then the oil is dripping in from above somewhere and filling the cylinders, and hasn't yet had a chance to "splash" on the sparkplug.
 

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There are oil passages from the block to the cylinder head to provide lubrication to the valve system. Is it possible that the passage is not sealed properly? If the oil control orifice was omitted excess oil may be supplied to the cylinder head?
 
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Discussion Starter · #18 ·
This sounds like a good theory, maybe the gasket isn't proper, thus covering the holes somewhat. To check, off come the jugs. Thye're not difficult to remove, but new gaskets are $50!
 

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When the bike is "parked" prior to is not restarting.... is it on the sidestand or on the center stand? if on the sidestand, then this would make the left cylinder more likely to "fill" with oil, which might cause it to send more blue smoke out of that side's exhaust.

This hypothesis does favor the valve seals.

So maybe improper assembly or even the wrong size were installed. Not sure if new valve stem seals were part of the rebuild.

However, if this theory is the prevailing one, then a proper compression test won't pick it up and a leak down test will be good as well. Correct?
 
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I've never wrenched on a CX500 motor but I've seen this thing run, and although it smells rich, its black smoke (like gas), and not blue smoke (like oil). But the amount of fresh, amber colored oil on the plugs 10 mins after a warm shutdown is impressive.
I really don't think it's going to be rings, you can't have that much blowby and have it not foul the plugs while running, and this bike runs like a top before shut off. As far as vacuum, I can't imagine the residual crankcase pressure or vacuum strong enough to pull oil into the cylinders, and where would it pull from? It would have to be PCV, a strangely bad head gasket, or through the head itself.
It's not over filled with oil, (unless you have the wrong dipstick) so that leaves......
valve guides and valve seals.
I think you would at the very least, need to pull the valve covers and rockers and look at the seals, wiggle the valvestems..... (my 2 cents).

I just thought about this one last simple test to tell if its rings or head. Get the motor nice and hot, then shut down and pull the plugs 10 min after shut down WITHOUT ever cranking the motor. If wet, maybe rings. If dry, then the oil is dripping in from above somewhere and filling the cylinders, and hasn't yet had a chance to "splash" on the sparkplug.
And that’s why clear, detailed information matters on a message board. It was far too easy to interpret the first post as the engine was “burning oil” instead of it pooling into the cylinder after shutdown.

With that in mind, I also agree with stem seals as the likely culprit.

I don’t think you’d have to wait 10 minutes after shut down either - pull the plugs right away and use a flashlight to watch for oil collecting in the cylinder.
 
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