Publishing instructions for MOC based on Lego Technic set
I think the key here is if you are trying to profit from it.  If you are doing this as a hobby, aka for fun, you have nothing to worry about.  If you are trying to sell the model and/or instructions, then you risk a friendly "Cease and Desist" letter from the Lego Group.  

Here is a paragraph from their "Fair Play Brochure":  

"For this reason, certain guidelines have
been developed to outline the proper
use of the LEGO Group’s trademarks and
copyrighted material for non-commercial
purposes in domain names and websites.
The LEGO Group’s trademarks and
copyrighted material may NEVER be
used by unrelated third parties for their
own commercial or marketing purposes,
unless formal permission or a written
licence has been granted by the LEGO
Group."  

Fair Play Brochure: https://www.lego.com/cdn/cs/legal/assets/blt1a4c9a959ce8e1cb/FairPlayBrochure.pdf