CBR 600F 1987 - 1990 CBR 600F Forum

Oil on spark plugs

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Old May 7, 2025 | 07:53 PM
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Moonlight2391's Avatar
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Default Oil on spark plugs

Tried to start it and it did not want to start, pulled the plugged and they were soaked with oil and gas, I have spark on all 4 but the oil I think is what is causing it because the plug itself is soaked in oil, now I checked the manual and I adjusted the timing and that did nothing, I took the carbs up to verify that the valves are opening and closing and they are but there is bubbles every time they do, i am going to do a compression test when I get the chance to see if it is the piston rings or valves that is leaking the oil, any thoughts on this? Can the oil be leaking from the valve stems?
 
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Old May 8, 2025 | 02:49 AM
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Ed Harris's Avatar
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From: UK,East Midlands
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Originally Posted by Moonlight2391
Tried to start it and it did not want to start, pulled the plugged and they were soaked with oil and gas, I have spark on all 4 but the oil I think is what is causing it because the plug itself is soaked in oil, now I checked the manual and I adjusted the timing and that did nothing, I took the carbs up to verify that the valves are opening and closing and they are but there is bubbles every time they do, i am going to do a compression test when I get the chance to see if it is the piston rings or valves that is leaking the oil, any thoughts on this? Can the oil be leaking from the valve stems?
Either down the valve stems or up the bores. From memory, if it smokes after being on the overrun it’s valves, if during heavy acceleration it’s the bores but that could be well off, it’s been a long time since I knew for certain.
 
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Old May 10, 2025 | 01:49 PM
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Originally Posted by Ed Harris
Either down the valve stems or up the bores. From memory, if it smokes after being on the overrun it’s valves, if during heavy acceleration it’s the bores but that could be well off, it’s been a long time since I knew for certain.
Can confirm although I'd change the valve diagnostic to be "if it hasn't been run". Oil drips down valves and pools on top, pours in when you fire the bike.

Smoke when you run is generally blowing past rings.

However, if you're going to fix one, just fix both. You'll have the whole top end off anyway. It isn't really that hard and if the cylinders aren't too bad (no major scoring) you might be able to do a light ball hone and a new set of rings, if the valve stems don't rock, a new set of seals.
 
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Old May 12, 2025 | 10:46 AM
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Moonlight2391's Avatar
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Originally Posted by heresolong
Can confirm although I'd change the valve diagnostic to be "if it hasn't been run". Oil drips down valves and pools on top, pours in when you fire the bike.

Smoke when you run is generally blowing past rings.

However, if you're going to fix one, just fix both. You'll have the whole top end off anyway. It isn't really that hard and if the cylinders aren't too bad (no major scoring) you might be able to do a light ball hone and a new set of rings, if the valve stems don't rock, a new set of seals.
it's been sitting for a year without being ran, I dropped the engine and checked the valves so everything is in spec, i replaced the cover gasket too. The oil is on the threads and seeing that I did not have this issue before I'm gonna say that from sitting the oil pooled in the valves, im tired of working on it at this point and I'm gonna hand it over to a shop to do. I spent $10,000 trying to get this thing as nice as possible for something to come up like this, I was considering getting rid of her and getting a newer bike but I'm already invested enough so I'm gonna go through with the shop doing it.

 
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