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MG MGB Technical - Metal fan fatigue

In the archives, there are quite a few horror stories about disintegrating metal fans on MGB engines. The three bladed fan on my ´64 18G engine looks quite healthy, but of course the thought is worrying.

Has anyone studied if there is a pattern in these breakages? Have they been bent, or are out of balance? Loose rivets? Or does it just happen? And how common is it?

Tore
Tore

Tore,

I've had one "fly-off". I'm not sure if its a solution but I visually examine periodicaly and check the rivets for tightness.

Paul
Paul Hanley

Quite a few? From my own watching of this and other fora I have heard of instances of the problem, probably only posted by others who have also heard of it but not experienced it. In the grand scheme of things it certainly isn't 'common', although individual examples of a fan where the blades have been pulled about by a PO for whatever reason may end in fracture and a blade sticking through an inner wing or bonnet.
Paul Hunt 2

Well there you are, proved wrong before I could even finish posting. But I still question 'quite a few'.
Paul Hunt 2

I took mine off, but a local doctor had the radiator ruined on his MGC by the fan breaking up.
Mike
Mike Howlett

Steve Simmons just had one come apart, see "plastic fans" on A board for pics and discussion; Barney has a picture of one on his site. I've seen them in person, and I've seen the three blade type shear the bolts off after running for a long time with bad grommets. Usually it results from damage that has been straightened = DON'T do it!
FRM
FR Millmore

I lost a blade from the metal fan on my 1100 midget. There was a loud "clang" and the whole car started to vibrate.

When I stopped, I found one of the blades (it was either 5 or 6 bladed) embedded in what was left of the fan shroud at the top. At least it saved the bonnet!


(Then there was the time that the oil pump fell off the block whilst I was trying for the 1100 land speed record....)
Martin Layton

Both metal and plastic fatigue are exacerbated, in my limited experience, as much by each individual unit's inherent weakness as any "design" flaw.

Units made up of components, such as a riveted fan have many opportunities to fail from poor component production (discrepencies in sheet metal integrity, discrepancies in riveting, discrepancies in metal flexibility or rigidity, or problems generated by harmonic vibrations as the fan cycles up and down thru RPMs).

Something like a fan is "balanced" as best as possible using assumptions about production variances, but the possibility of one fan of the many falling outside the acceptable limits for longevity is pretty real. If you were to look at balance vs. structural integrity of either metal or plastic the result is most likely a bell curve and some units, I would wager are destined to fall to the ends of that curve. One has to realize that most parts of our cars or drivelines usually follow this curve and should not be too surprised that some, even genuine replacement parts sometimes fail faster than others or in ways unanticipated even by engineers.

About all one can do is assume the worst and inspect such a device periodically to see if the usual problems (cracks, loosening fasteners, excessive flexing while accelerating the engine) manifest themselves, and then replacing or repairing the unit as necessary.
Bob Muenchausen

Indeed, the fan on my MGA just came apart but I was quite lucky. It didn't damage anything! The thread in the MGA section pretty much covers it, but I am still on the hunt for a plastic fan that will fit in the metal fan's place. I have a very good lead on one which I will post on if it works out.
Steve Simmons

This thread was discussed between 22/09/2006 and 25/09/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.