Clutch Fan Assembly 1968-70
The 1968 through 1970 roadsters were fitted with a fan clutch and a seven bladed fan. This was to help overcome the high under hood temperature of those models, running different ignition timing at idle. If this fails you can overheat at idle and damage a head. Nissan realized this flaw after replacing a few too many heads and came out with a spacer replacing the fan clutch completely. This recall basically locks the pulley and fan together as one assembly.
The original fan clutch consisted of a piece metal shaped almost like a "Q". A small wax pellet similar to what you find in on a thermostat and an outer pulley that would freewheel. Once the assembly heated up, the wax pellets would expand locking the fan up with the water pump pulley. The problem was those wax pellets were known to fail. When that happened the fan would freewheel and at idle that meant overheating. You can check to see if your car has the clutch set up by opening the hood and seeing if the fan will freewheel while cold. Warm it up and if everything is working the fan should no longer spin.
The 7 bladed fan is really overkill and quite noisy. You can get the same airflow and less noise with a 4 blade fan locked in place.
Nissan had the spacers when they had the recall. I would bet that part was no longer available long ago. From time to time you see someone selling a few they had made up. Or check with our vendors as they may have had a batch made up as well.
The fan is only really needed when you are sitting at idle as once you are at cruising speed the fan has almost no affect.
A note from Scott Sheeler on this subject: My experience, going back to the days when roadsters were in the shop every week or so, is that the fan clutch failures were caused primarily because of the "brake lining" band coming un-bonded from the ring hooked to the wax pellets. The loose brake lining would not lock down on the fan "drum" causing the fan to stay "disconnected". It's the same thing a you installing a set of brake shoes without the friction material - you aren't going to stop.
Just my two-cents.
Scott Sheeler http://thedatsunroadsterbook.com/(approve sites)