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TR4/4A TR4 Fan Hub Extension replacement

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J

jimitro

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I am planning to go with an electric cooling fan for my TR4
and replacing the stock fan hub extension with a light weight
alum. replacement.
Will this alum. replacement hub have any effect on the engine
performance as I thought the crankshaft needed the heavier
fan hub extension for balance.
Any thoughts on this?
Thanks for you help.
 
You'll get mixed opinions I think on this. The hub extension is considered to be a dampener for the crank, but reports of broken cranks without it are mixed. Neil Revington of RevintonTR in the UK has significant rally and performance engine experience, on his website he does not think removing the extension is going to cause issues especially in a non-race <5-6K RPM environment.

If you are just thinking of hopping things up a bit, also consider lightening the flywheel the next time the transmission is pulled.

Randy
 
Thanks for your input.
I'm going ahead with the switch.
As to lightening the flywheel, will this be ok with just
a stock engine as to the balance issue?
 
The dampening effect doesn't come from the extension itself; but from the rubber mounts for the steel fan. It's doubtful whether the factory intended it that way, especially since they later went to a plastic fan.

I do believe a dampener does help longevity, if you plan to exceed 5000 rpm continuously. But I've done perhaps 100,000 miles in my TR3A with no fan or extension and the original crank has held up fine. OTOH my relatively stock engine won't pull over 5K in top gear, so I've never run it up there for very long.

The aluminum flywheel seemed to work out well too; though others report problems with keeping them on the crank when racing. Unlike some American engines, Triumphs are all "internally balanced", meaning the crank is balanced without the clutch, flywheel, front hub, etc. and then all those components should be balanced separately. On top of that, the factory didn't worry overly much about balancing them, and since replacement pistons are much lighter than the stock ones, it likely needs balancing anyway.

But I did notice that it took more care to launch the car with the lightweight flywheel. Not hard especially, but harder than before (when I could basically just take my foot off the clutch and let it chug away) to not kill the engine.
 
If you are going to run your engine over 5000 rpm then get a crankshaft dampener from BME. If you build a very hot engine i might consider the ATI dampener since it is re-buildable and tune-able (they are expensive though).
trfourtune
 
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