How can you Adjust the chain drive on a john deere r72 riding mower?

Answer 1

I work on vintage British motorcycles so the chain drive on my son's R72 appeared equally arcane to me ,and we found it hard to find any service information on this hand-me-down mower. . The "adjustment" is really just moving the idler sprocket beneath the lower chain run to loosen (forward) or tighten (rearward) . The difficulty is that you cannot see much of what you are doing without either a lift table to work on ,or crawling underneath which is really impossible. So , to start , lift the plastic fuel tank upwards to allow it to be placed on top of the engine (not hot we hope!) , then using a 1/2" wrench and a ratchet and 1/2" socket remove the two bolts for the right side fuel tank support bracket. Place the bolts back in the bracket when you set it aside for now. Now you can look directly at the idler sprocket mechanism and the top of the chain run. The idler sprocket is held in place by a carriage bolt that slots into the right side frame bracket and has an L shaped piece added as a sort of guard or perhaps it was thought of as a handle for pulling/pushing by the JD people. Using a 9/16" wrench , loosen the locknut on the idler sprocket bolt sufficiently to allow you to move the assembly rearwards to tighten. I allowed a little slack in the top run , but not too loose or too tight . I've not seen the factory figurre for chain slack here but from M/C experience I'd say a "sag" of 1/2" in the top run should be OK. Too tight and you will stretch the chain ,too loose and the chain will jump the sprocket on the axle. Once the chain adjustment seems OK , tighten the idler sprocket bolt,making sure the L shaped piece did not drop downwards in the process of loosening and tightening , and RECHECK THE CHAIN TENSION AFTER YOU TIGHTEN THE BOLT , IT MAY HAVE GOTTEN TOO TIGHT! If so , go back and do it again --get it right. Other points to watch --worn chain or sprockets will not be improved by adjusting the tension. Lubricate the chain with spray on chain lube every week, at least , as they tend to run dry and hot .New chain is only about $25 from JD ,sprockets are hard to replace though.