Help with sprocket rpms

massey driver · Nov 28, 2009

I used to know how to do this stuff but have forgotten.Here's what I want to do I have a tiller that was driven off a tractor with a 1800 pto rpm and want to convert it to one with 540 pto rpm. I took the chain case cover off and here's what I have.The smaller sprocket [Driven one from the pto has 16 teeth and the other one has 40 teeth so in order for me to do what I want what size sprocket do I have to change the 40 tooth one to in order to get the same rpms.Hopefully someone can help me with this.Thanks Larry

zzvyb6 · Nov 28, 2009

Your 1800 rpm pto driving a 16 tooth sprocket paired to a 40 tooth sprocket delivers 720 rpm at the tiller shaft. (That seems a bit high to me, though. My Yanmar tiller goes a bit slower maybe because I never run at 540).

That being the case, a 12 tooth sprocket paired to your 16 will up the 540 pto to 720 at the tiller. Glad it didn't come out in a 1/2 tooth increment. You'd need a bridge.

In other words, to maintain the tiller rpm with 1/3 less pto rpm, you need 1/3 less tiller gear reduction.

massey driver · Nov 28, 2009

I thank you for your reply and info on what size sprocket to put in place of the 40 tooth sprocket.Your also right about it seeming like a high rpm as this is a exposed chain thats also driving more chains inside a oil bath gear box that I haven't opened up to see what there size is.I was hoping to just need to change the sprockets on the outer exposed cahin without having to go any further into the tiller.So gald to see that it'll be a easy thing for me to do in order get it working onto the newer tractor,without having to do to big of changes.Thanks again and now I can pickup what I need next week and start doing the changes that I need to do in order to have it working for next springs garden tilling season.As you can see this is a winter project and I'am glad its not going to end up being to costly of a change over.The other tractor was a MF 1655 with category o 3tph and the newer one is a MF gc2300 with category 1 3pth so other then needing to change that one sprocket I'll need to put in bigger 3pth pins as well as raise the top link by a few inches and of course change the pto shaft as well.So thanks again for your help as always Larry.