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Why might my spark plug be oily/black after running for no more than 5 minutes? Lot of blue exhaust smoke, too.

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The valves were just recently done and the guy I bought it from a year ago said he did the top end (I'm assuming he means he only did piston and rings, but he didn't go into detail). But after running for no more than 5 or so minutes the spark plug is always black and oily/shiny. I'm pretty sure the blueish/grey smoke is oil smoke, and when doing regular oil changes the oil is grey (which I've heard can be a bad clutch). What do I need to fix this problem? I'm hoping something as simple and cheap as new rings rather than a whole new top end altogether.

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only way to know is to take it apart. it is obviously leaking oil so you gotta take it apart anyway.

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first you get it all apart, then you measure various parts and compare them to the specifications. you probably need a micrometer, dial caliper and feeler gauges at least in order to check everything. you would probably check cylinder dia., piston diameter, ect.

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im pretty sure you might be able to check the rings without taking it apart. get a compression tester. warm up the engine, test compression, then put few drops of oil in the cylinder to help it seal up, and test compression again. if the compression stays about the same, your rings and cylinder are ok, and your problem is head gasket or valve guides.

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Good. Just ordered a compression tester yesterday (one day shipping, has yet to be delievered at end of day...) But I will do that and give results here. What is an ideal PSI for compression? I've heard 120-140 is pretty good. Obviously I know how to use the tester also.

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164 (+/- 21 psi) according to my haynes manual.

a repair manual is a nice thing to have. it gives all the info you need. its good to have even if you dont need to rebuild the whole engine.

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164 (+/- 21 psi) according to my haynes manual.

a repair manual is a nice thing to have. it gives all the info you need. its good to have even if you dont need to rebuild the whole engine.

Well unfortunately I got one that doesn't fit a 5/8 spark plug hole so I have to go to the hardware store and get an adapter. But 164 is my number to shoot for +/- 21 PSI. Doesn't FEEL like 164 but we'll have to see...

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you can do it in the bike but its easier when its out.

You'll have to remove the head/cylinder studs (while the head is still installed!) to do an in-frame top end rebuild. I'd advise you pull the extra 12 bolts (4 engine, 4 footpeg, 2 engine brace, 2 skid plate) and do it on the bench.

Once you've located the appropriate compression guage adapter and are ready to perform your compression test...

Be sure to hold the throttle wide open during the test; otherwise you will have a false low reading.

FWIW, my '98 did the exact same thing, cylinder was dusted (no air filter installed by previous owner). Bought a 120cc BBK for $169 and a couple jets. It's a weapon.

Edited by theraymondguy

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