I have a Lesco Renovator 20 and recently no matter what I do the drive chain keeps coming off. I adjusted the tension correctly, oiled the chain, etc and still it comes off. I replaced the large sprocket yesterday on the shaft since it appeared that the teeth were worn --- this did not help. Now I'm about to order the small sprocket which goes on the hydraulic pump. Could it be the chain???? Besides for this what could it be???? Its not complex... there is nothing hitting the chain causing it to come off. Thanks for your assitance.