TR2/3/3A engine fan assembly on TR3a: balance weight question

[2billydavies]

Hi everyone!
so I got my new fan parts in the mail yesterday, getting ready to bolt it back onto the engine (new fan, all the nuts, bolts, washers, rubber grommets, etc..). My question is this: the balance plate... how do I know how balanced the fan is, and what position to install this plate? My Haynes manual says that if I'm putting a new fan on, it should be "professionally balanced." Not really sure what this mean... how would I know if the fan is installed un-balanced? How important is this when putting it all back together.

I'm getting so close to starting her up. Moss has a sale going on... brand new radiators @ $100 off retail price. woot woot... order going out in the morning!

Thanks!

 

[TR3driver]

Basically what it means is that you need a balancing jig, which isn't worth buying yourself for a single use. For example, https://www.harborfreight.com/motorcycle-wheel-balancing-stand-98488.html
Check the factory workshop manual for more details, page C9 (or 151 in the Bentley reprint).

 

[Geo Hahn]

I ponder this when I changed my fans. I assumed the ideal approach would be to balance the fan and extension as a unit, then make some sort of witness mark so the bits could be reassembled on the engine in the same orientation. On my cars someone (possibly Standard-Triumph) had made such a mark by drilling thru the fan hub and weights and into the extension.

In the end I just rigged up a crude balance rod using a long socket and a couple of metal rulers to confirm that the fan itself was not particularly out of balance and then I installed it w/o any weights. Can't say if that was wise or not but I have driven long & far including cruises at steady RPM with no ill effects.

 

[TR3driver]

I assumed the ideal approach would be to balance the fan and extension as a unit, then make some sort of witness mark so the bits could be reassembled on the engine in the same orientation. On my cars someone (possibly Standard-Triumph) had made such a mark by drilling thru the fan hub and weights and into the extension.

Which is exactly the process documented in the workshop manual (as I referenced above). It stresses several times that the procedure should be repeated if components have been replaced, even filling in the witness mark on the extension with solder.