Fanbelt keeps slipping off?

Take the belts off, grab the outer rim of the pulley and pull hard from one edge as if you are flipping the rim off, if there is any noticeable movement you need a new pulley. (I'd bet as much as half a Freddo that there will be and you do)

 

Haha! That did make me laugh. 

I'll go give that a try shortly and report back...I was about to ask how do I see if it is the wheel but you've explained that perfectly. The only annoying part is I just redid the radiator and put new fluid in it, so it seems that will need to be drained out again. 

I suppose if the Crank isn't wobbly, then it must be the alternator being misaligned....if it still even works after it went for a swim that is. 
 

I do believe I owe you half a Freddo, 

Took the belts off, and put a slight amount of effort into wiggling the Crank wheel, it moved quite happily without much effort...so good news you found my problem! 

I'll be buying a new one and throwing it in asap. 

Thanks again 

Just to ask the question. Do I only replace this part? Or are there other parts I should be replacing as well? You mentioned the rubber Laminate, does that come with this bigjimny.com/store/jimny-gen3/crankshaft...-generic-m13a-engine or is that an additional item I need to get too?

It will depend on how equipped you are for getting the pulley bolt off. They are designed with a built-in flange washer and consequently the available surface area for rust can make getting them out an angry grinder job especially if you don't have access to a heavy impact wrench and even then it's not a guarantee that the bolt will cooperate. I don't know that I would necessarily order a new bolt with the pulley but I have a second jimny to use for a few days if I were to need it. As for the actual pulley the laminated bit is the ring you can see on the face of the pulley, it's one complete assembly as supplied. Just expect the crank pulley bolt to fight you is the main advice.