GRD-233 Engine Details
GRD Engine specifications, plugs, etc..
| Green Diamond: | Flat head, six cylinder | 50 net horsepower @ 3400 rpm |
| Firing Order: | 1-5-3-6-2-4, counter clockwise | |
| Spark Plugs: | Champion: J-11, gap: .028 – .032 | |
| Distributor: | Points: Standard #DR-2227XP | Gap: .018 to .024 |
| Condenser: Standard #DR-50X | Cap: Standard #DR-413 | Rotor: Standard #DR-158 |
| Coil: Standard #UC-14X (6 volt) | ||
| Oil Filter: | “sock style” | NAPA #1011 |
| Generator: | Regulator: Standard #VR-1 | Brushes: Standard #RX-51 |
| Fan Belt | Gates #558 gs | |
PDF 
Early GRD engines used the same 15mm spark plug as the HD 232 Champion D-16 gap set @ .025
my ID plate on my cab says 80 hp at 3400 rpm’s
My CTS-8 Manual says the 233 uses 14 mm spark plugs.
Champion # J-9-64
AC# 44-COM
Auto Lite# AN-5