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MG MGB Technical - v belt Fan

Hi
I removed the radiator off my 71 B to repair for a leak, and a close look at the fan it does not seems right.
the fan vanes are riveted facing the engine, not the radiator...i wonder if that is the right way...
thanks
Alf
alfredo

Hi Alfredo, If you look at the fan you will see that the blades are not flat but have a concave and a convex side to them. The fan should be fitted with the concave side facing the engine for maximum efficiency
Iain MacKintosh

thats the way they are, meaning that they are suppose to cool the engine pulling the air though the radiator.
thanks Ian
Alf
alfredo

First confirm that it *does* pull air though the radiator towards the engine. Turning the fan round doesn't change the direction of air flow but it does affect efficiency, as Iain says. Another point of recognition seems to be that the leading tip of the blades is rounded much more than the trailing tip, possibly for safety reasons i.e. fingers. In Clausager the one fan where it is visible does seem to have the blades rivetted to the engine side of the stubs which are part of the pulley.
Paul Hunt 2

I've just noticed that my fan seems to be the wrong way round, i.e. the concave faces of the blades face the radiator and the rounded corner is trailing. I did remove it and try to fit it the other way round, but the blades are not central to the central boss, but offset by about an inch towards the concave side (see picture, top half is concave side uppermost, bottom half is convex side uppermost). This means that when fitted (logically) the correct way round the blades would hit the crank pulley and alternator nut because at the moment there is only 7/8" clearance anyway. They would also be an inch further away from the radiator, and there is already a gap of 1 3/4". Moving the blades even further away from the radiator will result in a significant reduction in how much air it will pull *through* the radiator - not being ducted it will pull a significant amount of air across the back face of the radiator rather than through it when stationary, the losses from the increased gap quite probably being more than the gains from having the blades the right way round. As I've never had a cooling problem in even very hot (for England) weather, even with a rally plaque across the front of the front grille, I decided to leave things as they were.
Paul Hunt 2

Ooops.

Paul Hunt 2

Paul,

on cars for the European marked ('71 - '74), there was a 22mm wide light alloy spacer fitted between the pulley and the fan.
Seems that a p.o. of this car has canged the pump and 'lightened' the assambley a little.

Ralph
Ralph

I changed the pump, and the new must have been the same as the old as I changed the pulley over and it still lines up correctly. I did think about a spacer, which does seem to be part of the 7-bladed plastic fan, but not the 3-bladed metal I have. I'd need much longer bolts if it had a spacer, they don't engage by many thread as it is. The two fans are very different - the metal having a flat centre boss and the plastic a deeply dished one. From the drawing and the orientation of both fan and spacer it looks like the spacer is simply to fill this dish, simply to bring the bolt heads out to the front of the dish rather than hiding them deep inside, which would make access very difficult short of removing the radiator. From page 66 in Clausager the plastic fan looks to have very similar clearance to radiator and alternator as my metal fan does fitted the 'wrong' way round. Of course, if the fan is put *too* close to the radiator the it is likely to cut a big hole in it under heavy braking or (God forbid) impact.
Paul Hunt 2

Paul,

there is a spacer for the 3 blade fan, the 7 blades one is fitted directly to the pulley without this item.
Moss UK quotes the following numbers in their catalogue:

12H 3910 Spacer- Water pump 18V engines with 3 blade metal fan.
This assy uses different bolts. They are listed as SH 604151 for the 18V with fan spacer.

For cars fitted with a 7 blade plastic fan, there is no spacer fitted but a clamping ring (CAM 1599) in front of the fan.

BTW, locktaps for the metal version are 12H 1388, two needed.

Ralph
Ralph

Thanks, that *is* clearer, better than the Parts Catalogue. I'll have to see if I can get one.
Paul Hunt 2

iam happy that this clears a fan issue...
but i have bigger nightmare, i have changed the alternator(bearings shot), a recon. radiator has been fitted,(old one had a leak), the thermostato and water pump are ok...replace everything and still overheats.
look at where i should have in the first place( run engine without radiator cap) and some air bubbles came up...what now?? where to start?
thks

alfredo

Alfredo, it looks like bearing in mind your comment about the air bubbles that your cylinder head gasket is leaking. This will mean removal of the head and replacement but be sure to have the head refaced otherwise you risk blowing the gasket again.
Iain MacKintosh

You need to determine whether the bubbles contain exhaust gases or not with a combustion leak detector - http://www.toolsnstuff.co.uk/product_info.php?products_id=17418 - first before diving into it any futher. I had a similar problem on my V8, the bubbles were clean. In the end I think it was the water pump sucking in air, and I've heard of this happening if the bottom hose connections are a bit loose as well.
Paul Hunt 2

yes they contain exaust fumes, therefore iam going to strip it and ask for technical advice from a mechanic friend.
thks
alfredo

This thread was discussed between 08/08/2007 and 28/08/2007

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