eprovenzano
05-24-2010, 02:23 AM
I have a 99 400EX. Over the last winter I decided it was time to overhaul the engine. It was still on the original piston and rings, and yes smoked like a 2 stroke. So I had the valves redone, new valve seals etc. I had the cylinder honed, as it was still on the original bore size. A new piston (std size), rings and gasket kit and I put it back together. The never really ran "right". The bike would idle and then you could hear an air escape from the engine, and it would stumble and then it sometimes would stall, or catch itself and go on.
My son rode the bike and it seemed fine. He even commented it ran really well, it even had more power than before the rebuild, and no smoke. Next week he goes for another ride, this time I get the call... "Dad the quad died and won't start". He commented it seemed to get hot and then died. So after dragging the quad home from 2 miles deep in the woods, the tear down began.
Valves were fine; timing was dead on... pull the head, ouch. The piston was not pretty, the rings were stuck, and the cylinder was scored....
So after a through search, and a lot of head scratching, I've concluded the head gasket was the culprit. The layers seemed to have delaminated, and I believe allowed the engine to go lean, and sticking the rings.
Fast forward a few weeks, a fresh overbore of the cylinder (2 over), new OEM gaskets, new piston, and rngs. It now runs smoother than after the 1st rebuild. It idles good, it rev's good, it just seems to run better.
Oh well that's my saga. I've done a few heat cycles, and it should be ready to full bore after one more heat cycle.
Thanks for listening.
My son rode the bike and it seemed fine. He even commented it ran really well, it even had more power than before the rebuild, and no smoke. Next week he goes for another ride, this time I get the call... "Dad the quad died and won't start". He commented it seemed to get hot and then died. So after dragging the quad home from 2 miles deep in the woods, the tear down began.
Valves were fine; timing was dead on... pull the head, ouch. The piston was not pretty, the rings were stuck, and the cylinder was scored....
So after a through search, and a lot of head scratching, I've concluded the head gasket was the culprit. The layers seemed to have delaminated, and I believe allowed the engine to go lean, and sticking the rings.
Fast forward a few weeks, a fresh overbore of the cylinder (2 over), new OEM gaskets, new piston, and rngs. It now runs smoother than after the 1st rebuild. It idles good, it rev's good, it just seems to run better.
Oh well that's my saga. I've done a few heat cycles, and it should be ready to full bore after one more heat cycle.
Thanks for listening.