Other Effects About HHO generators have no known harmful effects on healthy engines. 

HHO generator manufacturers often assert that oxyhydrogen helps clean carbon deposits from the engine's valves, but that's unlikely since HHO gas has no solvent effect whatsoever. 

Large amounts of quick- burning HHO in the cylinder itself may help to burn off some oil residue from the piston and cylinder head,hydrogen welding but this premise hasn't been tested thoroughly enough to confirm.