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Hello all, new to me 1998 Boss Hoss zz4 - bike was running great while I was getting comfortable with the handling on side streets. I took the bike out on the freeway for a 20 mile excursion and noticed the exhaust sounded different on the exit ramp. I get home and noticed bluish grey smoke coming out of the exhaust when I rev the motor. I checked the compression in all cylinders and found cylinder 7 with no compression. The other cylinders ranged from 203 to 220.
Any thoughts?

Do a leak down of the cylinder. Which means to pressurize the cylinder with air when its at top dead center. They have kits to rent at the autopart stores providing your in the U.S. Listen for air at the carb, exhaust pipe, and dipstick or oil fill. Air at carb means intake valve issue, air at exhaust valve issue, and at dipstick, oil fill or oil pan means rings. Good luck.

Thanks for the reply, I'll let ya know what I find.

I pulled the valve cover off and found cylinder 7s intake pushrod had popped out from under rocker - is this common for the ZZ4?

Stuck valve. IF the push rod is out Then the valve should
be closed. With no compression, the valve must be opened... Hence stuck valve. This was a common happening on the ZZ2 in the early 90"s...

Paul H

It could also be a broken valve spring.

Sooooo - the rocker bolt was super loose - I replaced all the rocker bolts with locking ones and now the engine runs great again, crisis averted almost, while working on the bike I noticed that the frame frame was cracked up by the neck - jeezzzzzzzz

It's important to periodically check all areas of the frame for cracks. With age, the torque of the engine and the flexing of the metal tubing may cause small fractures in welds and the surrounding areas.

Do you have any photos?
I thought these were cracks in my frame below the headstock - but they're not.