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Honda Makes Changes to GX390 Engines

When the new management team took over MMRA in 2002, one of our goals was to keep the rules for engines as consistent as possible from year to year.  We have been fortunate that we have been able to do this for four years, but there is a necessary change being made for the 2006 season.

Honda Engines has changed all their GX line of small engines from K1 to U1, representing a new country of origin for the engines.  While they are basically the same, there are two differences to note.  The crank and rod design in the new U1 motors are different from the old K1 motors.  An "old" and "new" crank are pictured below:

Rob Stambaugh is a member of the MMRA Competition Committee and he also works closely with QMA.  Rob confirmed that all GX engines have changed to the U designation and QMA is also being forced to modify their rules.

As such, the MMRA Competition Committee voted to allow new U1 motors, and to allow racers with the old K1 motors to replace their crank and rod with the new U1 crank and rod if they so choose.  This is not required, it is just a legal option for racers with old engines.

In the great tradition of MMRA, here is a FAQ (Frequently Asked Questions)

1.  Do I have to upgrade to the new crank and rod?

No - it is optional.  Check with your engine builder to see if they recommend the new crank and rod for performance or durability reasons.

2.  Why is MMRA allowing this new crank and rod?

There is no other option.  All new engines are coming this way.  If we outlawed the new crank and rod, we would force new car buyers to find an old engine for their car.  Eventually, these old engines would run out and we would stop any potential growth in the sport.  The best we can do is to minimize expense for existing racers by allowing them to just replace their crank and rod instead of buying a whole new engine.

3.  Can you tell the difference from outside the motor?

No - the only way to tell which crank and rod an engine has is to take the engine apart.

4.  Are there other rules changes for minicup motors in 2006?

No - this is the only change approved by the MMRA Competition Committee.  If you are ready to get your engine freshened, you can send it off now to get ready for next season.

5.  When will the new 2006 rulebooks be posted?

They will be posted late this year.

6.  What would changing my crank and rod cost?

In the EES Catalog, cranks cost $241 and rods cost $87.05 - the total cost to changeover will depend on the amount of labor involved.  Also, other engine builders may charge more or less than these figures.

7.  Is there a way to save money on this?

Tim O'Brien of Extreme Engine Systems will be at the MMRA Awards Banquet on November 5 in Nashville, TN.  If you bring your motor to the banquet, you can give it to Tim for freshening and/or sealing with MMRA Approved seals.  This will save you shipping costs.

8.  I have a different question.

No problem - please send an e-mail to and we will get you an answer.