I have a 1986 honda helix, runs great, but has a engine vibration at low speed only 15 to 25 mph, past that point smooth , took off drive pulley , still vibrates , the crank has some end play , scracths on cover from fins on pulley ,suggest it is moving in and out at times , crankshaft has very little movement when running but virbration from frame to front plastic is loud ,need help tom