which bike to use?

[Sleazy Santa]

I've got three possible frame for making me motorbike from outta..
aluminum Iron horse Maverick 2006 or 7 mountainbike
aluminum GT Avalanche 2008 frame (use most parts from iron horse)
probably steel Diomondback 2005-7 28"wheels hybrid

wondering which'd be best for me to attach an engine to. I'm going cross country this summer on one.. just not sure which.
thanks yall

 

[leftywoody]

My personal opinion is to use a steel frame only . I tried alum. and it is too fragile .Strong frames are a must .

 

[stuartracing]

I did a Trek on my last one and it was ok, bent the rear axle somehow...Now I bought a cheap beach cruise of Craigs list and it`s doing pretty good for a el cheapo bike.....I see no difference from the $300 TREK to the $50 BC. I did weld in some bracing though in the rear by the axle and a tube going from the upper tube going from the neck to the seat post to the down tube up on the steering neck....Just to be safe....