09-03-2018, 10:42 AM
Here's my thoughts on what happened. I assume the onset of the vibration was fairly sudden, and it wasn't ridden much after it started. The visible scuffing on the pistons and cylinders is not abnormal. Four cylinder engines running on 3 cylinders don't really vibrate more, so I don't think the bent valve is the cause - maybe just a red herring here.
The carbon buildup may be caused by a poorly re-mapped ECM that causes it to run rich - or something like leaking injector(s) or a fuel pump with a regulator that is out of spec. That can be tested easily by the dealer with a fuel pressure gauge, turning the key on momentarily to energize the pump, and see if pressure bleeds off. Its should be 50psi, not higher, and should hold for 10 min.
The likely cause of the vibration is a bent rod(s) from hydrolocking, from fuel or water filling a cylinder before it is cranked. It happened several times on 1979 CBXs that developed sudden vibrations. They were left on the sidestand with the fuel valve left on, one of the float needles might stick open, and fuel would fill the primary airbox and fill the far left cylinder (vacuum petcock added in 1980).
I have also seen plenty of bent rods on ATVs are submerged, but also that are pressure-washed and water is shot into the exhaust or intake and into the cylinder.
When they pull the head off again, they could put each piston at TDC and see if one or more does not come up as high. It would be pretty noticeable, maybe 5-8mm difference.
The carbon buildup may be caused by a poorly re-mapped ECM that causes it to run rich - or something like leaking injector(s) or a fuel pump with a regulator that is out of spec. That can be tested easily by the dealer with a fuel pressure gauge, turning the key on momentarily to energize the pump, and see if pressure bleeds off. Its should be 50psi, not higher, and should hold for 10 min.
The likely cause of the vibration is a bent rod(s) from hydrolocking, from fuel or water filling a cylinder before it is cranked. It happened several times on 1979 CBXs that developed sudden vibrations. They were left on the sidestand with the fuel valve left on, one of the float needles might stick open, and fuel would fill the primary airbox and fill the far left cylinder (vacuum petcock added in 1980).
I have also seen plenty of bent rods on ATVs are submerged, but also that are pressure-washed and water is shot into the exhaust or intake and into the cylinder.
When they pull the head off again, they could put each piston at TDC and see if one or more does not come up as high. It would be pretty noticeable, maybe 5-8mm difference.