Hi, I have a small 4 cycle 1000 watt inverter type generator, 50 cc engine and it burn oil, big puff on start up and when running, I have to refill after 5 hours. It use about i would say 1/3 of a cup of oil. When new it did not use any, it looks like it started all of a sudden.

I took it appart, it has a diagonal split casing, never seen this before. The intake valve is fairly clean but the exhaust valve was full of hard black carbon. The stem looks good. The exhaust is well coated with black carbon.
The intake valve has a rubber type seal but the exhaust one ride on something like a sleeve, no rubber, no seal.

The piston looks pretty good and the cylinder is not scratched.

Could it be the rings?, The valve?

Also, do you know any internet dealer for parts on these thing. I also need the torque on the bolt for the casing, the piston arm, the flywheel nut.

Thanks,

Please post the engine model no.
thanks,

The generator is a small Yamaha EF1000is, on the engine it says 7VV 50CM 3. It is a 4 cycle with the casing splitting in diagonal.

A blown head gasket or the rings would be my guess. I could not find any free information available for your generator, but I did find a place online that you can buy parts from and they sell a service manual for you generator. The service manual is pricey at $55.00 + shipping, I guess thats why theres no freebies online.

http://www.yamahagenerators.com/home.php

I took the thing appart, is it possible to see if the rings are worn??

The book is quite expansive, I will order the rings tomorow, do I have to replace the piston, it look pretty good, the engine is only 3 years old.

I took the thing appart, is it possible to see if the rings are worn??
Take your old rings off of the piston, then insert each ring one at a time into the cylinder and use the piston to push it down about half way, then check the ring end gap. I don't know what reject is for your engine but I would say if the gap is much more then .025" - .030" the rings have substantial wear. Remove the ring and try the next one. The oil ring tend to have a little more clearance the the compression and scraper ring, but it should not be excessive.

You can also have cylinder wear, but if your engine has a cast iron sleeve then wear is most likely minimal and you could tell if you have a noticeable ridge at the top of the cylinder.

Has the engine received normal maintenance at the normal intervals? Internal wear is usually attributed to dirty air filters, dirty oil, low oil levels, or old oil that has been used beyond it's life.

Did you ever fix the issue Mietsu? I have an EF1000iS with the same issue. I have the motor apart and it is exactly as you described.

i too have this same issues...

does anyone know what the valve clearances are??

too line up the crank and cam look for the dot on thier respective cogs... remember, look for the dots, not the spring-mount holes that look like the dot...