gsinal 1 #1 Posted April 11, 2012 got a 520hc with onan 20hp and i do know the oil was changed yearly and the motor was kept clean of dirt build up in the cooling fins. It burns a little oil less than a pint in two tours of grass cutting cutting an arce a tour. It has 1200 hrs on it and dont know if the carbon removal job has been done to it. If i were to do it now is it too late. It still runs good. And if i put seafoam in the oil before the oil change will i hurt the motor with the potential of all the carbon build up breaking loose and moving thru the motor. Would like to do the carbon removal job as soon as i can get another tractor to do the grass cutting. Any insight on the situation would be greatful. Share this post Link to post Share on other sites
refracman 167 #2 Posted April 11, 2012 As the saying goes better late then never. The job takes about 3hrs at most and is fairly easy, parts including oil change is around $75 Onan recommends carbon removal and valve adjustment every 600 hrs. I believe that the they do have a bit of carbon builtup at 600hrs, but it is more for the valve adjustment. Onan valves actually tighten up not loosen up with age, which is unlike the other brands. Also around this amount of hrs some of these engines loose the valve seats, contributing factor ? Share this post Link to post Share on other sites
