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MG MGA - Fan failure

This happened on the MG80th (SE Car Club)run at the weekend, gave the owner quite a fright and an unexpected power bulge, also damage to the rad top plate.

MGA 1500

Dave Swinburne

Oh, wow! That's frightening. A friend of mine with an early MGB had a blade slice right through the bonnet at about 50 mph.
He had heard a clicking sound that he couldn't diagnose on the side of the road.
He found out what it was:>( In that case the rivets had failed.
I try to check mine occasionally for loose rivets etc by trying to move the blades relative to the fan. I don't know if I would see a crack on the main fan structure though, probably not.


I wonder why this is happening so often? Saw an MGA at MG1996 where the broken fan blade had stuck in the bonnet brace, and know a friend who lost a blade on his MGA on his drive home from GT33. And last month a member of our Club had an MGB's metal blade break off and go through the radiator bottom.
Is it aging, poor material, or just the flexing? Seems that rivet failure is unusual.
Any ideas?
P. Tilbury

The fan seems to have more holes than normal. Maybe this is a contributing factor to the damage?.................mike
m.j. moore

I actually checked my fan for cracks using a dye penetrant inspection kit. I didn't find anything, so hopefully that means this won't happen to my car. I have a couple other fans around, so I'm tempted to check those also to see if I can find any cracking in progress.
Del Rawlins

But it did not crack through a hole.
P. Tilbury

This event gets more common with age and metal fatigue. I had one like that in the mid 90's with about 195,000 miles on the car, likely the original fan blade. I have swapped engines and fan blades a couple of times since. I have never magnafluxed a fan blade, but it is a good idea. I ALWAYS take a very close look at the fan blade whenever I have one in my hands.

Due to dynamics of combined centrifugal force and gravity, highest stress on the fan blade comes just after bottom dead center. Result is the most common direction for the blade to fly is upward to the right, commonly taking out the top radiator pipe, the end of the fan guard, part of the bonnet steel frame, and sometimes putting a dimple in the alloy bonnet skin. Many a bonnet has been saved by the fan guard. In years past I have seen a few holes in the bonnet where the blade sliced right through.
Barney Gaylord

This is scary stuff! Are plastic fans less likely to fly to pieces? Is there a plastic fan that will fit a standard MGA water pump and not hit the rad? What about a viscous-coupled fan? Come on, someone must be able to answer these questions!
Lindsay Sampford

This happened to me on my 1600 and put a nasty dent in the bonnet. I had the used "original" replacement fan magnafluxed and welded in weak areas then ground down. I had the fan of my 1500 magnafluxed and no cracks were found. It is metal fatique and I would highly recommend magnafluxing to look for stress fractures. Welding will meld the metal obviously and strengthen the fan blades. Unless I'm wrong and running on borrowed time... someone will correct me if I'm wrong, I trust. Just saying, that was what I did to combat a potential flying fan blade.
David Holmes

Mine let go on the highway about three years ago. I guess 50 years was a pretty good run. Fortunately mine shot down and did no damage except for a scratch on the steering rack bolt. The blade was just laying there on the cross member when I finally pulled off the road. That's about as lucky as it gets!
Steve S

I'd be a little wary of automatically assuming that welding will increase strength. It could induce stress concentrations especially if the fan is not annealed after welding.
J H Cole

I provided a new fan to my friend after his A shed a blade at Watkins Glen Vintage last year. Blade went down, not up, and he never saw it. Engine vibrated so badly he thought it lost a rod. He had it flat bedded home. It's a shame, he could have removed the fan and driven it home.

Cars are not the only thing that shed blades. Jet engines do it to! And believe me, you don't want to be around when they do. One of the first tests I was involved in as a young engineer was simulating the loss of a compressor fan blade on a JT9D (747 engine). The ensuing imbalance ripped the test rig loose from the floor and shook the test cell! Great fun!
Once saw an OV10 that shed the turbine blades. Engine nacell and fuselage were riddled with holes. Luckily, nobody was riding in the back!

G T Foster

NTG in Ipswich has new plastic fans in MGA pattern

Part number is B103DZ, price is GBP 32.90.

dominic clancy

The basic design of the MGA fan and also pulley is very poor and was not any good in 1960.

At that time nobody really cared too much as most cars were less than reliable anyway.

The answer to the problem is to fit a plastic fan as identified by Dominic and an MGB front pulley.
Robert (Bob) Midget Turbo

One problem with the new radiators is the bottom pan. It has a lip that sticks out past the face of the core about 1/4". I installed a Texas cooler with a new radiator and the plastic blades just nicked this lip, bent the blades up into the core and tore both to pieces. I installed a new radiator again with this lip and the original metal fan again just nicked this lip so I ground this lip off a bit and bent the blades back about 1/16". While bending the blades I found a crack had started so I welded it up. Think it is time for a new fan! Have a good day!

John Progess

Why a B pulley bob

Dominic, I have fitted the NTG injection moulded fan to my car and it works really well. It is of a larger diameter and has a much more efficient blade design than the standard metal fan.
(The first time I revved the engine with my head under the bonnet it blew my baseball cap off!)

It has brought the running temperature down by 10 degrees from 175F to 165F at the expense of quite a lot more fan noise.

In other words it runs much cooler but it sounds quite a lot more like a double decker bus than I would like!

I was warned that the injected moulded fan could begin to flex in high ambient temperatures causing it to foul the radiator and I have seen evidence of this on other MGAs which have this fan fitted.
Fortunately, the radiator in my car has been spaced forwards by 10 or 15 mm and this extra clearance seems to have solved this problem.

So, thus far, and with the extra radiator clearance above, I would definitely recommend it.


The picture is taken using a wide angle lens with the radiator removed and makes the fan look bigger than it really is.

Colyn Firth

I forgot to add that the larger diameter of the injection moulded fan meant that I had to adjust the finger guard on the back of the radiator header tank very slightly to prevent the fan from fouling on it.

Colyn Firth


Dominic has always had the problem that his engine runs too cool, even with the original fan. I recall that he has fitted a radiator blind to get the temperature up. The NTG fan looks a decent bit of kit.

Peter, if I have it right, the B pulley has a 'shock absorber' rubber moulding in the centre of it. At least that's what mine seems to look like.

Steve Gyles

Peter and Steve

The reason for choosing the MGB pulley is 3 fold
Firstly as you rightly say the MGB pulley is harmonically damped
Secondly the original MGA pulley is riveted together and fails just as regularly (IMO)as the fan the MGB one is not!
Third you should then use the MGB timing cover with the far better oil seal!! :)
Bob Turbo Midget England

I can't use a B crank pulley with the Judson - no way to mount the extra IVVI for the Judson drive belts. The pulley I have is a one pice from aluminium cylinder stock, so there are no rivets to fly apart.

The fact that the new fans make the car run cooler are probably a problem, but I'll have to wait and see how the new engine is on temp before I take that decision.
dominic clancy

Are the NEW metal MGA fans OK? I see Brown and Gammons has them.
Lindsay Sampford

This thread was discussed between 19/10/2010 and 21/10/2010

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