Nissan Repair: engine vibration, engine vibration, piston rings

Question
I own a Nissan FB14 1997-98 model (Automatic) engine no begins with GA. the problem of late is that the engine tends to vibrate and the car stalls. the mechanic i go to changed the spark plugs. even this has not resolved the problem as the plugs get black. first it was only 01 plug now its 02. what do you think is the problem & is it safe to drive like this?when this problem occurs smoke come out of the exhaust and i get the smell of burning oil. the mechanic says the piston rings  have to be changed along with the gasket. pls advise. thanks a lot


Answer
Hi Maas -

Before you condemn the piston rings, I would take a compression test for each cylinder. If the compression is low (more than 20% less than the other cylinders), then squirt some oil in the cylinder and take it again. If the compression improves, then it is the rings.

Please note the color of the smoke coming out of the exhaust - if it is black, it is because the engine is running rich, and you have a fuel problem. If it is more on the blue side, and kind of lingers in the air, that's burning oil. Might want to also take a look at the valve seals too, that is a common problem when cars burn oil.

If the car stalls, it should be loked at right away and not driven.

Hope this helps -
calvin