Replace or motivate a contractor?

[Grant Liddle]

I have an extremely complicated, difficult and large project of restoring a 1900's duplex.  It has been gutted to the bones and needed significant structural repairs.  It needed the center beam running under the party wall to be replaced and the roof was incorrectly built.  It was originally a slant roof, but along the way they decided to get more room and built a hip roof on top of the old wall of the slant roof.  The roof repair is significant and involved due to the way they added the hip roof.  Several new supports need to be added and all the floor joist needed to be upgraded from the orignial 2x4's in order to safely use this space.  The property was acquired for such a low price it justified these repairs.  The contractor I eventually found via another investor contact.  He is knowledgeable and definitely competent however...prior to his working on my project he came with financial baggage.  He also is a poor estimator on both the contract price and time.  He gives bids that are too low but will stick to his word and complete the work.  This causes a majority of his financial issues as his contracts exceed his original time frame then he loose money.  I have additionally compensated him in some of these cases on my project to make it more fair for him.  

He eventually completed the 40' long steel beam repair and lifted the house 4+ inches back into place.  It is amazing and perfectly done! He then started on the attic framing, truck issues sprinkled with these financial difficulties sent him off looking for other sources of income.  He would find hopeful in-out work that was always more complicated and set my project back weeks.  Finding another contractor able to complete the complicated attic repair at this point would be difficult and I have no other leads and not sure even where to find such a contractor. My question is does anyone have suggestions on where to look for a good structural framing contractor? or is there a way I can keep my financially burdened contractor on my project and incent him to not take any other projects until mine is complete?  The original contract date was not upheld due to his poor estimating skills and transportation issues.  He is still committed and comes to work but keeps taking other jobs to supplement which always end in setting him back even further and delaying my project.  I can't move on until this framing is done so I'm a bit stuck.  Any suggestions as to what to do to keep my project moving would be appreciated.