A few people spoke about doing this. There were a lot of positives and also a lot of negatives.
Personally I think its a good idea, but you will need to include some kind of disclaimer form for people to sign upon recieving them and sending them back to say they got them in good condition and they have been returned in good condition. And a FULL PRICE deposit just incase something goes wrong or they dont come back.
Then you need to take into account how long people will use/need them for as you may get some people keeping hold of them and say "oh i havent had a chance to do it yet" so best stick a hire period time/price in there. I was lucky enough to have a fellow member who lives local (clio_stu) let me borrow his and i had no problems giving him something for it even though he never asked.
You will get people coming along and saying "why not just leave it to specialist's, this is encouraging people who dont know what theyre doing to take the job on and f**k it up". Dont let that put you off your idea. At the end of the day, its only an engine (meaning it's not life threatening to have a go yourself)