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Electric Fans and Keeping Things Balanced

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John_Hensleigh

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I figured this would have been discussed already, but didn't find anything in my searches.

I am converting my TR4 for autocross/light road race use, and want to use an electric cooling fan in place of the stock 4-blade fan. I'd like to remove the (now unused) fan extension/hub. I've read in some places that the extension acts as a dampener for the crankshaft harmonics at 4200 and 6000 rpm, and that removing it is detrimental to the crankshaft. Other sources say it is perfectly alright to run without the extension.

Racetorations sells a kit they say replaces the damping effect of the extension ($350 before shipping and VAT). Patton Machine, Revington TR, etc sell flanges that essentially replace the inner flange of the extension (~$50) without specifically claiming any damping effects.

Any thoughts on this? Thanks in advance.
 
It's not the extension that acts as a dampener, but the fan and the rubber inserts that it rides on.

The problem is real, I've seen the broken crankshafts. But the problem only happens under fairly specific circumstances (all other stresses in the crank being near maximum, plus prolonged operation at an rpm that excites the natural resonance of the crankshaft) and likely takes a long time to actually break the crank. (That is to say, it only takes the stress in the crank into the region where it starts to fatigue, rather than breaking immediately.) So many people are "getting by" without a dampener of any sort.

I've been running without one for many years and never had a problem. But I already have a damper to install on my next motor. Falls in the category of cheap insurance, IMO.

You might check with Ken Gillanders at BFE. Don't know if he still has them but he used to offer a lower cost kit (orignally developed by TriumphTune) that uses the damper from a 5-main MGB.
https://www.britishframeandengine.com/parts1.html

I opted for the more expensive kit, which also converts to a narrow belt and has alloy pulleys for the water pump & generator/alternator. Likely the same thing that Racetorations offers, but Ken gets a volume discount on shipping from the UK (meaning the overall price may be less).

Note that you should not have to pay VAT on parts shipped out of the UK. Normally the vendor will simply not collect the VAT, but if they do, there is a way to file with their tax agency to get it back.
 
I don't doubt broken cranks, obviously that is an issue. However, I don't know that I'm convinced that the dampener (or lack thereof) is the cause. My impression is that the stock crank just wasn't meant to be flogged as it approaches 50 years old. Some break, many don't. I'm inclined to believe that failures are more attributable to 50 year old parts using (at least) 50 year old technology than to the absence of fan extensions. If someone feels differently about it, please warn me off.

I wouldn't be surprised if I tear down the engine every winter, at least for the first half-dozen seasons. That way I can check tolerances on everything, make sure nothing is fatiguing prematurely, etc.
 
TR3/4 cranks were breaking 50 years ago. Often times, they broke when <span style="font-weight: bold">not</span> flogging them around, sometimes at speeds much lower then the red line. There are some harmonics at various speeds that sometimes are just the straw that breaks the crank's back.

However, in all reality, it really isn't an everyday event. Just be prudent and if you remove the fan, put on a damper. Of course, I have one of Ken's (British Frame & Engine) damper and pulley set on my TR3. Peace of mind you know... :laugh:
 
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