You are correct. The BBB only requests that the complaint be reviewed by the other party. If the party comes back and concludes they have done a thorough and timely review, the BBB really cannot do anything. The first party has the right to rebuttal, but again, that may go nowhere too. The BBB only wants to insure the complaint was timely reviewed. It has not way to force and outcome on either side.

Playing devil's advocate, I really would give the engine company the benefit of the doubt before blasting them on the board. Again, if you are not and expert in this area or do not have the results back or your own independent results it is really a matter of your word vs their's. Most companies are probably not out to get you and it is highly possible that when calling their cust service person, they were not a true expert either, did not understand what exactly the issue was, or you could have misunderstood as well. My point is this, keep your head up. Be patient for the results. We all know or have experienced crazy mechanical issues before in our lives and this could just be one of those cases. I think it is wierd that it ran fine for 7000 miles before this issue popped up. Best of luck to you.