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MG MGB Technical - Fan Position on 72B

I'll start off admitting that this is going to be one of my oddest inquiries, but this is what I get for 2nd guessing myself sometimes.

Yesterday, while installing my rebuilt distributor - I was of course looking closely at the engine to make sure everything was connected correctly and tools were out of the way for starting engine. My neighbor is looking things over too, as we didn't want to nick the timing light or send some tool flying.

We both wound up looking at the fan, and it looked funny; like it was facing the wrong way for air flow.

Out came 1/2 dozen books, parts manuals, etc., but no consensus could be found on which was the front or backside of the fan.

So.... 72B 1800 6 blade metal fan, yellow!

I have the aluminum spacer between the fan and pulley.

I have the fan installed so the ribbits are towards the engine,not the radiator.

I have yet to find a clean photo of this arrangement, and in some parts catalogs it even appears that the spacer is between the fan and the radiator, which is rather odd too!

My question: Should the ribbit support arms face the radiator, or the engine?

Thanks for humoring me this morning.

BobA

R.W Anderson

sorry to say but you have it in reverse. Change the fan around so that the support brackets are in the front facing the radiator.
Sandy
S Sanders

See http://www.mgb-stuff.org.uk/coolingtext.htm#mfans

It all depends on whether you have a long-nose or short-nose pump and pulley. If you have a short-nose pump you usually have a short pulley and the spacer goes between pulley and fan, with long screws. With no spacer the blades clatter the engine.

A long-nose pump and pulley needs no spacer, and short screws. A spacer between pulley and blades would put the blades very close to the rad.

However a third option may be a short-nose pump, a long-nose pulley, the spacer inside the pulley, and long screws!

The only reason I can see for having the spacer on the front of the fan is if a longer pump and pulley were fitted in place of short and the fitter didn't have the shorter screws, but that would put the spacer very close to the rad.

The fans themselves add more options to the mix. 3-blade metal and 7-blade plastic at least are handed, in that the central boss is closer to one side or the other. The correct orientation of the metal fan is with the smoother (more efficient) face of the blades facing the engine, which puts the ribs the blades are attached to facing the radiator. If a short-nose pump and pulley is fitted, and the spacer is missing (as mine was when it came to me), then fitting the fan the right way round the blades will clatter the engine. In this case mounting the fan the *wrong* way round maintains the correct spacing between blades, engine and rad, at the expense of some efficiency. However having run the car with both orientations for some years the difference is marginal I'd say, I got a far more noticeable improvement in cooling by adding the foam block between radiator and mounting panel - not that cooling has ever been an issue anyway.
PaulH Solihull

Thanks for the input. We both look at the fan and thought the air flow/blades were backwards. I'll reverse the fan so the brackets the blades are attached to face the engine and I'll retain the spacer between the engine and the fan.

Now to get some band aids ready for the knuckles while removing the long bolts and turning fan around. I've learned to place a sheet of cardboard along radiator to protect fingers and knuckles.
R.W Anderson

RW - "Now to get some band aids ready for the knuckles"

Just put a strip of duct tape over your knuckles to avoid the need for band aids later. Cheers - Dave
David DuBois

Or a piece of thick card across the back of the rad to protect the fins *and* the knuckles ...
PaulH Solihull

Paul,

You mention the foam (that was fitted by the factory but missing on most B's). I fitted that too and the difference is indeed noticable; dail not on N but slightly on the left of it and in hot weather the temperature stays lower. Attached is a picture of it.

Willem vd Veer

Not sure if yours is a single strip or not. Mine was two offset strips glued together, but after the first trip out I found the forward strip almost completely detached from the one that was glued to the the mounting panel, and very little sign of gluing between the two. Used my own glue and it has been fine since, I'd have been really peeved to have lost it.

PaulH Solihull

I have the rubber seal on the metal ridge above the radiator, but I do not have the foam seal between the radiator and the metal ridge/frame.

I'll add the foam seal soon.

I haven't gotten around to flipping fan around yet.

Now to move on to my next topic in another posting.

Thanks.

R.W Anderson

Paul,

I found my foam at the office when the where rearranging the server room, but it looks remarkably like yours :-).

It is one piece, the original does have a step in it, mine doesn't. It did come wit a glue-strip at the back so it stays in place for now.
Willem vd Veer

Follow-up question:

My 7 blade fan is steel, very heavy. I've seen listing for 7 blade plastic fans, $100 range new.

I heard suggestions that if I could, I should switch to the plastic fan to decease weight and drag on the engine/water pump.

Is there an advantage to switching from steel to plastic, and if yes, is it worth the price?

Thanks.
R.W Anderson

Might reduce drag on the *fan belt*, with an increase of noise from the greater number of blades. As long as any fan is balanced it will have no effect on the water pump at all. Worth $100? No way, Pedro (as Del-boy said).
PaulH Solihull

For $100 I'd install an electric fan. Oh wait -- I did! ;-)
Rob Edwards

I'd save $100 and do neither! It shouldn't be needed!
PaulH Solihull

I concur with leaving the stock 7 bladed metal fan in place. I've been running one for going on 40 years with no problems. RAY
rjm RAY

Well, the electric fan uses infinitely less HP when it's not running -- which is most of the time! ;-)
Rob Edwards

Does the use of electric fans as replacements for metal or plastic fans explain my difficulty in searching the net to find photos of fans on engines in MGBs. The vast majority of engine photos show no fan on the engine. Just an empty plate where the fan would go. Or are all these folks, driving in cooler summer temperatures?

I'm leaving mine alone for now, sticking with the metal 7 blade.
R.W Anderson

Mechanical fans until Sept 76 for the 77 model year, electric after that. So there should be more *cars* with mechanical fans than electric. But if you are looking at uninstalled *engines*, then they may well not have fans fitted, or even water pumps. I would imagine very few are driving without either, and there should be no need to install electric in place of mechanical if everything is working correctly, even in desert states.
PaulH Solihull

This thread was discussed between 14/02/2011 and 24/02/2011

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