TR2/3/3A TR3A - Dynamo Fan is loose!

[angelfj1]

Yes, I know, "dynamo" isn't a word that you hear very often these days. I just think it is way too cool not to use.

Seriously, on the way home from FALLFEST 2012,this past Saturday, the Grey Lady was running great, and I was enjoying the open air motoring until I reached the NJ - PA bridge across the Delaware. I had slowed down for the E-Z Pass lane and was beginning to accelerate when a horrible shrill sound started. It reminded me of the noise made by a slipping power-steering belt. As soon as I had the opportunity I pulled off the road and popped the bonnet. I also noticed that the engine vital signs were normal, temp approx. 180F and oil pressure at 50psi.
With the engine at idle the sound was somewhat less, so I goosed the carb linkage and the sound became louder and now sounded more like shaking a tin can filled with loose nuts and bolts. I turned off the engine and had a closer look. So, I figured I should focus on the rotating parts because the noise got louder as engine speed increased. I checked the fan belt tension - OK. However when looking closely at the dynamo, I noticed that the fan was free to rotate. WTF? Now, how could that be, and aside from the noise, what would be the consequence of running without the benefit of fan cooling?

So, let me ask, has anyone experienced this problem. I have not been able to find a good drawing showing how the fan is secured. It appears that the fan is sandwiched between a step in the shaft and the pulley. Should there be a key way in the fan hole? None of my Lucas docs show a dynamo with a fan attached, so I assume that this feature was optional.

Anyone have a solution?

Thanks in advance, Frank

 

[TR3driver]

Tighten the nut!

The fan does have a notch to fit over the Woodruff key, but at least on my generators the spacer is short enough that the fan fits down behind the key and is held only by being clamped in place between the pulley and the spacer. If your fan is loose enough to rattle around, then the pulley is loose too and complete failure is not far behind.

Since this happened in the daytime with (presumably) the lights off and little load on the dynamo, I doubt there was any damage due to lack of the fan. But the windings inside do create a good deal of heat, and will overheat if operated very long at full load and no fan. The heat damages the enamel insulation and allows inter-winding shorts, which of course increase the heat and the end result is an armature good only for display as an objet d'art.

There is supposed to be a lockwasher between the nut & pulley, but since it has come loose once already, a drop of Loctite might be a good idea too.

 

[Don Elliott]

Frank - I took this photo a few years ago when I discovered that the aluminium casting had broken. I replaced that with a spare and it's still working fine.

Notice the key near the tip of the screwdriver. That is what Randall is talking about.

Cheers - Don

 

[angelfj1]

Thanks Don.