Recently I acquired a rancher 28151. It unfortunately suffered a broken chain but despite reviewing forum posts, looking at the manual and studying parts lists I still can't determine if it's the primary chain or secondary...
Hello Lockstock I do not have a parts list, but I can help with the terminology.
A primary chain is the first chain used from the engine. A secondary chain must run in sequence from that.
In your first image I guess the belt is from the engine. This would mean the sprocket [LH in your image] is the first driven chain - the primary. It drives the secondary chain [RH in your image] to the rear axle.
Hope that helps. ---------------------------------- Jack
Looking at the photo it would be the primary chain as above. However that info is pretty much useless as genuine spares for these are extinct these days. It is normal I think 3/8 chain. Better off going to a power transmission place and buying either a length or a box, either way fairly cheap. Plus if 1 has gone it is likely neither have ever seen lube so best to replace both.
As an update I was able to pick up a replacement chain from the local mower shop and installed it relatively easily with the master link meaning I didn't have to remove the auto drive system.
The result was promising with the mower starting and driving both in forward and reverse. There does however appear to be some slack in the chain and the occasional but somewhat frequent clunking sound coming from under the seat when driving. As it only really occur when moving it difficult to ascertain exactly what is causing it.
I'll try to post a video of the slack in the chain and some sound (which I think is normal) coming from the drive when I had it on the jack.
