View Full Version : Balancing a radiator fan(?)

05-14-2012, 10:31 PM
What's the general opinion on balancing a radiator fan? The remounting hardware I ordered came with balancing weights. But, I can tell you there were none on the fan when I removed it this weekend.



05-15-2012, 03:09 AM
I'm guessing it varies with normal manufacturing tolerances. The original fan on my 56 TR3 didn't have (or appear to need) any weight; but I wouldn't take that to mean that none of them do.

05-15-2012, 07:31 AM
When I removed the fan on my TR3A, it had two of those balancing weights on it. IIRC, the factory service manual mentions something about balancing the fan. Of course, there probably aren't too many TRs running around out there that have had there fans balanced once they were removed for the first time. I think it's more important to make sure that the blades are in line and there are no cracks etc. Also, it would be a good idea to replace the rubber bushings and lockplate.

Geo Hahn
05-15-2012, 01:30 PM
I'm probably not the best qualified to answer that:


Though I doubt either failure was due to imbalance.

05-15-2012, 01:46 PM
Oh, that'll buff right out !

Geo Hahn
05-15-2012, 03:30 PM
Oh, that'll buff right out !

Alas, the 'outie' bonnet dent it made would not...


Got lucky on the 2nd one... it hit the bonnet support and ricocheted downward.

05-15-2012, 08:29 PM
Aloha Bob,

The factory marked the balanced fan assembly by drilling a small hole through the pieces and fan down to the hub extention. This was to make a reference point so if nencessary it could be taken apart and reassembled and still reatain balance. If you are using the original fan and hub extention, a good start is to line up these holes. In Geo's photo you can see the hole on the fan blade on the right in the 12 o'clock position. Since you didn't have balancing weight on disassembly, you may not need them. The locking plate is fairly symmetrical, light in weight and close to the center of rotation so I think it will have very great affect on balance. The tab washer plates can only be mounted between the same bolts as the were originally so I don't think these will influence balance.

05-15-2012, 08:40 PM
Here's something I responded to on the TRA site.


Geo Hahn
05-15-2012, 08:47 PM
That procedure seems to just balance the fan -- but I think the original set-up calls for the fan and hub to be balanced as an assembled unit (hence the reference hole mentioned that is drilled thru the fan and into the face of the hub).

05-15-2012, 09:52 PM
It also calls for the pulley halves to be installed.

05-15-2012, 09:58 PM

Got it, thanks. I note the pin hole in the fan and see how it lines up with the pin hole in the hub. Makes sense to me.

Frank, I'll just double check the balance using your method but, since there were no weights when it came off, I doubt I will add any weights unless it is grossly out of balance (which I doubt).

New rubber bushings,locking plates and hardware going on.



05-16-2012, 08:25 AM
That procedure seems to just balance the fan

So, that was the original question, wasn't it? :yesnod:

The hub has a much larger mass but small radius of gyration, and thus easier to balance and perhaps less effect on the balance of the fan-hub assembly.

An ideal case would be to balance the entire assembly from fan to flywheel, assuming that other components have been considered, e.g. con rods, pistons, etc. I understand this is routine in race car engine assembly.


But, considering the fan alone, these are known to self-destruct. If you balance the fan and check that the rivets are tight, you can avoid the metal fatigue in the blades and possibly a damaged radiator. :smile:

05-17-2012, 07:11 PM
i also broke a fan blade while driving did not damage any thing. i bought a plastic yellow fan from trf said it does not need balanced. runs great.

05-18-2012, 09:06 AM
I am just thinking here...

It seems that balancing the fan would not have any affect on the fan assembly itself...as you are not modifying the assembly, but rather just compensating for their imbalance at the bolts. So the blades and rivets would seem to be a simple matter of fatigue, from flaws or later damage...but not likely from the imbalance. In other words, the blades have no idea wheather the balance weights are on or not. They will still be imbalanced after the weights are added, the weights just compensate for their imbalance.

The balancing would really only seem to matter to the hub extension and the front of the crankshaft...as they will receive all the stress from an imbalance. If the fan is balanced, the hub extension will see zero extra load. If the fan is unbalanced, the hub sees all the extra load...and the crank sees even more, as the extension acts like a lever.

Anyway, like I said...just trying to think it through here. I think the balancing is for the crank longevity, and not for the fan assembly.


05-18-2012, 09:31 AM
I dunno, vibration does strange things, especially if you find a resonant spot. The fan would possibly get violent shaking in addition to its normal stress as a fan; which might be enough to make it flex and work harden.

At any rate, the book specifically mentions balancing the fan, without saying a word about balancing other components. Could just be coincidence or a tech writer's whim; but I have a suspicion there was a deeper reason.

Geo Hahn
05-18-2012, 09:58 AM
...the book specifically mentions balancing the fan, without saying a word about balancing other components. Could just be coincidence or a tech writer's whim; but I have a suspicion there was a deeper reason.

As I recall the factory team had some misadventures at Le Mans with a couple of fans.

05-19-2012, 06:03 AM
So that is an original tr4 fan Geo? To start with it does not look very symmetrical. The blades look like they would pulsate between blade patterns, like a one two one two. Many years ago, (1982) I bought a parts car that had a bent tropical fan on it. The blades had it radiator just a little. I took a pair of sheet metal tongs and a hammer straightened it out, and have driving it for 20 years that way. Sounds good runs great.

05-19-2012, 11:09 AM
Yes, those are original TR4/TR4A fans in Geo's picture. I'm thankful I never had an issue with it yet!


Geo Hahn
05-19-2012, 03:17 PM
The original fans had a lot of aluminum extending beyond the thich=k steel cruciform and thus (perhaps) were more prone to flexing, breaking or other damage than the tropical fan which has much less aluminum hanging out there.