Using IRA or Solo 401K to lend to Auto Dealership

[Rav Ram]

I have a friend who buys and sells cars at the auto auction and wants to somehow figure out a way to work together with me using my money and no other real resources (i'm not involved in business). I want to avoid UBIT (Or all possible business taxes) so I am thinking the best way to approach this is lending him say $20K, secured by the cars he buys, and charging a loan fee of some type (like points or $1,000 per vehicle) Plus interest, for each car he buys and sells. I would love to just say "Ok, we split all profits" and he will agree to that, but saying that, from my research results in Unrelated Business Income Tax which is almost like investing with my own funds. The same concept can be applied to say wanting to partner with someone to start other types of businesses.... like a Food Truck. You want to split profits, but not run afoul of the UBIT restrictions. This may be an advanced question, but I would love to hear your feedback on this.

1) Any ideas on what i'm thinking...

2) Has anyone done this type of loan? Any idea where I can get sample 401K loan agreements?