what is the cause of my engine vibrates when I speed up from 90km/hr and above. on 1996 Honda Accord

recently I have a problems with engine vibrates. I sent to workshop for repair. Found engine oil already flow into the sparkplug compartment. Workshop told me the engine need to be top overhaul, change piston ring, gasket kit, grind valve and cut chamber head, change oil filter. after repair the engine loss power, and vibrate when speed exceed 90km per hour and above. Please advised. thank you

Asked by for the 1996 Honda Accord