Originally Posted by grizz1

No - the GX Series cannot use the older 28-0600 rod. They require the newer 21-0600 rod.
Here is a post I did a few weeks ago on the subject. It might help to clear things up -

"CRANK SHAFTS
Gen 5.5, GX Series TiNi and MG66 TiNi coated cranks can be fitted to all Generations of GO engines - but you must use the right con rod.

CON RODS
The new Pro Con Rod (part # 21-0600) can only be fitted to the Gen 5.5, GX Series TiNi, and MG66 TiNi cranks. This rod is NOT compatible with any Gen 5 or earlier motor.
The Gen 5 and earlier motors require the older Pro Con Rod (part # 28-0600)
Reason being the differing crank pin sizes and internal diameters of the con rod big end bushings given by Massive Mods in his earlier post.

TiNi WRIST PINS
These are compatible with all the GO motors."


FYI -

Gen 5.5, GX, MG66 - Rod ID = 5 mm & crank pin dia = 4.993 mm

Gen 5 and earlier - Rod ID = 4.98 mm & crank pin dia = 4.973

You can see the problem. New rod is too sloppy on the old crank, and the old rod is too tight on the new crank.