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MG MGA - MGB Asymmetric Fan

In my recent thread about painting my radiator I made reference to fitting an MGB 7-Blade asymmetric fan, so I thought I would open a specific thread to gather the points together under an appropriate heading.

To start, it's worth pointing out that Moss list two MGB 7-bladed fans, the less expensive one has a conventional blade layout, being evenly spaced. The more expensive one (50/$75) has eneven spacing between some of the blades. It is the latter that I purchased.

The fan is the same diameter as the MGA fan and fore/aft clearance between the engine and radiator is very similar. In fact the blades have more clearance with the dynamo/alternator spindle nut without make any fitting alterations. The distance between opposite mounting holes is however reduced from the 6cm with the MGA fan to 4.5cm. It is therefore important to check that your water pump has the alternate mounting holes (my pump has 8 holes so that either fan can be installed.

I have only done one 30 min run in zero OAT so it is too early to give a firm conclusion on temperature control. However, for the record, the engine ran at 170-173 at a steady 70mph. My normal is usually 175.

I considered the fan quieter than the MGA fan (I don't use a shroud). The car felt livelier and the exhaust note more pronounced - wonderful. Whether this was due to the cold still day I cannot be certain, so I will have to wait for a warmer day to conduct more trials. The thought crossed my mind that the vastly increased airflow through the engine bay may perhaps be allowing the carbs to breath better. Worth a mention that I had the same sort of feeling when I did trials with my home made stub stacks and that proved correct when trialled on a rolling road.

Steve




Steve Gyles

Steve, I wish I had tried the 7-blade in between experimenting with the NTG 6-blade, before I then went on to try the single electric fan and finally the twin electric fans. It would have been good to compare the performance of the two.

I would have expected that the 7-blade would use up a little bit more bhp than the stock metal fan as it pushes much more air but it would be interesting to actually measure this on a dyno.

You realise that in fitting a non standard fan you have taken your first step towards the electric fan "dark side"! :-)

You cool running guys have at times made me feel a little like Gollum in Lord of the Rings in trying you tempt you with the "Precious Ring". The Ring" being the 5 to 6 extra bhp you could gain most of the time if you fitted twin electric fans instead of the engine driven fan :-)

Cheers

Gollum.

Oops I meant,

Colyn.

(Dont forget to send us a pic of the painted rad Steve)


c firth

Colyn

To offset your BHP comment, the plastic fan is so light compared to the metal 6-blader. How does that alter the computations? I should have weighed it before fitting but I would hazard a guess at it being about quarter of the weight.

Steve
Steve Gyles

Barney has a brief discussion of this fan on his website, see Tech Article CO - 104A.
George G.

Thanks George. Interesting background information.

Steve
Steve Gyles

I installed the same 7-blade asymmetrical fan on my MGA on May 6, 2015. The plastic fan is 1/4-inch larger diameter than the original steel fan, so I had to trim my metal fan shroud a bit. I think the Moss plastic fan is a bit quieter, and it moves more air, and it seem to lower running temperature a bit (maybe not quite as much as 10dF).

Oddly, mine tossed a couple of blades on July 16, 2-1/2 months and a bit more than 10,600 miles later. No way to know why it happened. No collateral damage. We drove it that way another month and 3000 miles, as it didn't seem to be notably out of balance (no noticeable vibration). In August I installed another plastic fan (same model). Have done nearly 14,000 miles since then with no problem.


Barney Gaylord

I must admit thatI never considered the weight factor when I tried the plastic fan Steve.

The bhp figures came from a conversation I had with Peter Burgess when my car (which at that time had the big NTG plastic fan fitted) was on his dyno a couple of years ago.

He said that the 6 bhp improvement that his setting up had found for me on the engine could probably be almost doubled if I took the NTG plastic fan off.

Cheers

Gollum, oops

Colyn :-)

c firth

Colyn

Barney's was even lighter!!!! Reading his short article in his technical website, I did not realise that the asymmetric fan was originally an MG design. I had just assumed that Moss had come up with something new.

Steve
Steve Gyles

As Barney has done significant travelling with the fan I would be interested to hear if he has noticed any temperature difference in slow running/stationary traffic. The reason I ask is that I just got caught in a queue behind a very slow tractor for almost 10 minutes, crawling along at 5-10mph max with the concertina effect. Far from my temperature creeping up from its previous 172-173 cruising it actually started dropping and stabilised at 160. Later, when I got back home, I sat idling for almost 10 mins to observe and the needle never rose from 173. So my initial thoughts are that this fan works very well at these low/stationary speeds and just may be very useful for carb cooling etc. Perhaps early days to be making these deductions as it is still quite cool outside - currently +8 centigrade, but I frequently go out in these sort of temps and have not noticed this before.

Thoughts?

Steve

PS. It's either the quietness of the fan or its efficiency, but I am still convinced in my mind that the engine is livelier and 'raspier'.
Steve Gyles

Steve,
My NTG big fan definitely dropped the engines running temp by 10 degrees F when I fitted it and so I would expect your 7 blade Moss fan to be at least as good.

Colyn
c firth

Interesting stuff guys, this might be my first upgrade when I get my first MGA nest week.
Jack New Forest

I have just found out the weights of both fans. See Chicagoland MG Car Club: http://www.chicagolandmgclub.com/techtips/mgt/cooling.html

The MGA metal 6-bladed fan is 633.32gms.
The MGB plastic asymmetric 7-bladed fan is 170.09gms.

Therefore the latter fan is 3.72 times lighter. Quite a difference. My guess above of it being a quarter of the weight was almost spot on.

Steve
Steve Gyles

Interesting thread. I was wondering if there is a similar fan too fit the standard MGA set up?
Graham V

Graham

I am not aware of them doing one at 6cm holes. You will need to look at your water pump boss and pulley. It is always possible you have the additional holes at 4.5cm. If not, it's not a major job to drill out and tap the holes. A machine shop would do it for you if it is not your skill set.

Steve
Steve Gyles

Steve...I mentioned on another post that my 6 blade steel fan was about 800gm...just reweighed on an accurate scale and it was 777gm . Either mine is a special designed as an additional flywheel or .....
Just bought one of the plastic units from moss...
Neil Ferguson

Steve...for info I ordered th fan shown below and from Moss US . It is specifically for the MGA ..so Moss now have the asymmetric fan for the A and the B. The part number is 434-332 and it costs about $56....plus post.
I could not find it online in Moss UK.


Neil Ferguson

Neil

I typed the code in and it came up on the UK site costing 28.75: http://www.moss-europe.co.uk/catalog/product/view/id/15815/s/fan-cooling-7-blades-plastic-ahh6999z/

I wonder why mine cost 49.00?! Looks the same other than the bolt holes look 6cm apart.

Steve
Steve Gyles

That looks good - thanks for the link Steve - another job for mine before the summer
Cam Cunningham

I have to admit to being a trifle confused. This link should show both fans: http://www.moss-europe.co.uk/catalogsearch/result/index/?limit=all&q=cooling+fan&search_group=8987 - need to scroll well down.

Essentially the same 7-bladed asymmetric design, although the blade profile looks a tadge different unless they have posted one of fan views from the other side. The less expensive one looks like the 6cm bolt holes for the MGA. Big difference in price for the same article - different quality plastic?

Steve
Steve Gyles

Steve..when I was doing my internet search I came across a recent moss us flyer saying certain items have been reduced in price..amongst them was the plastic asymmetric fan for A and B . From memory reduction was from about $77 to current $56 . I also checked LBC site and their before discount price was still the $77 .....
I believe The big price differentials are a result of a mix of old and new sales bumf....and not different plastics
Current moss uk price of around 28 quid looks excellent .....
Neil Ferguson

Steve, I looked a both the links you sent, the fan seems a good upgrade for 28, but the link says MGB, does it fit the 1500 mga engine ?
Jack New Forest

Jack

It may fit. It depends on the measurement of the fan's opposite bolt holes and whether the 1500 pump has the same. I guess we will soon find out from Neil.

Steve
Steve Gyles

Just been into Moss. I can confirm the 29 fan has MGA spaced holes. I.e. 6cm opposite holes.

Steve
Steve Gyles

Steve,
Snap. We must have passed each other en-route!

My metal fan weighed in at 790g (must have a lot more paint on it than yours!) whilst the plastic one is 161g (Slightly lighter than yours).

Also, when laying the metal one on a flat glass plate, it rocks all over the place so had some fine balance issues.

regards
Colin
Colin Manley

Colin

Small world. The fan I just mentioned is part no. AHH6999Z.

The only observation I would make is that the mounting boss is recessed in on both sides by 1+cm. I will be interested to hear if you need spacers to mount it on the pulley boss or whether the the fan boss slips over the pulley boss. Unlike my fan which is flush on the mounting side.

Steve
Steve Gyles

I would be interested in feed back if anyone fits one of these 29 fans, ie. Was it a straight swap or did you encounter issues.
Jack New Forest

Being the doubting Thomas type, I do wonder if this replacement fan gives any worthwhile advantage over the standard metal one? I have to think it doubtful. If there is any advantage it is presumably only when stationary in traffic and not under moving draft conditions. Someone did mention the concern of the original fan being prone to shedding blades but on inspecting mine it seems very solid and substantial. Hopefully no-one is expecting the plastic fan to help with overheating when on the move.
Think I will leave well alone!
Bruce.
Bruce Mayo

Bruce

I have only done about an hour of driving to date. What I have noticed so far is a lot more air blowing; approx 5 degrees F lower in normal driving; temp actually dropping in very slow moving traffic; idling increased by 50 to 100 RPM; and all is much quieter. I haven't found a negative yet.

With all those factors I would not write it off too fast. Worth getting more feed back from others.

Steve
Steve Gyles

Allvery interesting. I had always understood the fan is really only of use at slow/no speed anyway.
I fancy trying one out but will probably have to leave it a couple of months
Graham V

Bruce,
when I ran my car with the NTG plastic fan fitted, the engine temperature dropped by 10 degrees F at ALL speeds (including high motorway speeds), when compared to the temperatures it ran at when I had the standard fan fitted.

This was the start point of my theory that the airflow through the MGAs radiator grille is very much reduced at high roadspeeds because it struggles to escape from the engine compartment.

I think it is slowed down so much that the engine driven fan becomes a really important provider of cooling airflow through the radiator at high road speeds as well as when the car is stationary in traffic.

I know that I am pretty much on my own with this theory but I cant think of any other reason that would explain the engine running so much cooler at high road speeds when you fit a more effective fan to it.

Steve, I'm afraid that the laws of aerodynamics and Newtons 3rd law will will tend to work against your impression that your engine seems to have a bit more power with the new fan.

If its blowing more air it will be also using more power to do it although, because it is a more efficient design, it probably won't use so much more than the standard fan.

Colyn
c firth

Colyn

The raw engine and exhaust sound was more obvious and it got me thinking why as I was driving along. Getting an improved engine/exhaust note usually creates that feeling of better performance. More likely of course it was simply the relative quietness from the fan allowed me to hear other noises. However, just for a bit of mischief, you mentioned that the car has trouble getting rid of the air out of the engine bay, so just may be that extra air is being rammed in by the more efficient fan and is creating a very marginal over pressure than normal, helping the carbs to breathe slightly more at a stroke - not talking anything mega, just a tadge. Not talking supercharger stuff, more like the incremental increase we got with the stub stacks.

Steve
Steve Gyles

Never thought about the ram air effect of the fans Steve.

Maybe we should fit an even more powerfull fan and, taking Sir Christopher Cockerells advice, fit flexible skirts to make it hover! :-)

Colyn
c firth

I have just done another trial run. At 70mph my temp gauge sat at my standard 175 and did not budge. As soon as I dropped back down to 60 and below the temp also dropped and sat solidly at 170.

The more interesting findings I got out of the run surrounded the half dozen or so cotton threads I taped around the bonnet, including one each of the MGA vents. The cotton on the right hand side went inwards (as anticipated) above 15 to 20 mph. However, the left hand one (by the carbs) fluttered quite happily outwards up to the 70 mph mark (I did not go any faster so can't comment higher than that). At a standstill that cotton was almost vertical (quite a blast) but the right hand one was lifting by less than half of the left.

So, what do I conclude from that? It would seem that the fan is providing a noticeable increase of air down the carb side and sufficient to provide the carbs with all the cooling and air supply they need, perhaps vindicating my earlier comments that the car felt livelier. The relatively reduced airflow on the right side may well be due to obstruction by the 4" trunking to the heating unit.

I also had tapes up my bonnet centreline. They all fluttered straight rearwards to the bonnet hinge line. So, with my more raked sports screen it would appear that the airflow stagnation point is much closer to the screen than the standard.

Steve
Steve Gyles

That's a good investigation report - thanks Steve
Cam Cunningham

I found a similar effect Steve during my experiments with different types of fan set ups.

With the original metal fan fitted my car would very occasionally suffer vapour lock symptoms when stood in traffic.
This ceased to happen after I fitted the NTG plastic fan and similarly, it never happens with my present twin electric fan set up.

I agree in that I think the increased volume of air blowing into the engine compartment is helping to keep the float chambers a little cooler.

Colyn
c firth

Colyn

Bye bye bilge fans!!

Meant to mention that Idle seems to have gone up 150 to 200 RPM, rather than the 0dd 50 that I noticed the other day.

Steve
Steve Gyles

You've sold it to me Steve I'm ordering one of those 29 fans from Moss.
Jack New Forest

Steve,
The face of the mounting boss is dimensionally in the same place as original and fits over the pulley boss. The material at this point is just wider all the way to provide a full width landing for the root of the blades, unlike the metal one where the base is twisted where it rivets to the blades.

regards
Colin


Colin Manley

Good to hear Colin. I think there will be a lot of sales of that fan this year. I was going to say have your had a test drive yet? Then I noticed no dynamo pulley nor fan belt.

Steve
Steve Gyles

.......and no radiator!!
Steve Gyles

Colin
Do you have a standard MGA set up? I have a Mk 2 and would be interested to hear if its a straight swap. From Steve's very helpful research it appears it will fit, but it would be nice to be sure.
I assume there was no radiator in your picture as it is no longer required with the new fan :)

Thanks Graham
Graham V

Graham,
Yes, all standard, so should fit nicely.

Regards
Colin
Colin Manley

Even the original clips on the hoses too Colin!
Cam Cunningham

Thanks - thats the AHH6999Z 28.75 ?
Graham V

I am in the middle of my engine rebuild to go back in the car after 30+ years and reading all the comments about the asymmetric fan and the MGA shroud I am wondering if one or the other would improve cooling. Is it worth fitting either or both to my 1600 engine.
Thanks Brian
Brian Paddon

Brian

I guess for anyone who has a hot running MGA then every little improvement helps. However, in my opinion if you suffer from overheating then you should operate on the cancer first and not just apply a sticking plaster. For instance getting the radiator sorted with the correct MGA core will always be my recommendation.

Where I am thinking the fan may be of most use is in traffic queues on a hot day. It may just be the answer to the vapour lock issues we suffer with modern fuels.

As you will have read above it is also lighter, pushes more air and unlikely to cause catastrophic damage compared to the metal fan in the event of blade failure.

Steve
Steve Gyles

Brian

The best approach to getting adequate cooling is to

1. set the timing correctly, with a little retard from factory setting to adjust for unleaded fuel
2. set the mixture correctly and not too lean
3. Have a standard pattern radiator in good condition, as this will let enough air through to cool the engine.
4. Make sure you have clean coolant passages in the engine. there are apparently good chemical approaches to this.
5. run the correct mix of water and antifreeze

All other modifications are addressing only the symptoms of other problem(s). A standard MGA in good mechanical order doesn't overheat
dominic clancy

Graham,
Yes, that's the part number of my fan.

regards
Colin
Colin Manley

Thanks Colin
Graham V

I generally agree with Dominic's comments but I would make one more point. Having had As for 46 years and having done a lot of miles (30k miles per year) in my early days I don't remember in those days this obsession with water temperatures or suffering from vapour lock despite commuting daily into Birmingham and cruising very long distances at higher speeds in the pre speed limit early 70s.

It is my believe that something has changed and this is modern fuels run hotter hence causing the vapour lock issue. I think the engine temp is usually a non issue, it doesn't matter whether you run at 180 or 190, all that matters is that the temp doesn't go through the roof in any situation.

Paul
Paul Dean

Paul

I think the point here is that in the older days, when radiators sprang leaks, there were plenty of repair shops in possession of MGA-type replacement cores. Nowadays, probably due to cost/demand/expense that core layout does not exist except with just one or two specialists. Instead we now have radiator shops and manufacturers putting modern mass produced core layouts into our tanks. They simply do not work.

Steve
Steve Gyles

A comment about basic thermodynamics . The heat transfer from the water in the radiator to the air is primarily a function of the surface area , the coefficient of heat transfer for the surface and the velocity and temperature ( and temp. rise ) of the air coolant passing over it . If you have an inefficient radiator as many current offerings seem to be ..due to poor core layout ( ie reduced surface area ) then this can be compensated by increased airflow ...ie a better fan. . This nothing to do with treating a cancer with sticking plaster as someone mentioned above .....it is about basic heat transfer and getting the energy transfer right ..even for an inefficient radiator.
Neil Ferguson

...I would add that replacing the horrible inefficient clunker of a heavy , riveted 6 blade potentially destructive ( and occasionally actively destructive ) 6 blade fan with something that does the job much much better is to me a non brainer..but I am not a purist ...even mg did it late 60s as Ii understand .....as BG always adds .... my 2p!
Neil Ferguson

Steve

Yes I accept that. As I said I was adding to Domic's list that included this point. And yes I followed your lead last winter and have one of Bob's core's. My main point is whether fuel ran cooler in the old days, and whether I am right in saying we didn't get vapour lock, well at least in UK?

Paul
Paul Dean

When unleaded fuel surfaced, the clear advice we to retard ignition settings by two or three degrees. I suspect this has in time been forgotten.

Too much advance causes overheating.

Ergo

If the ignition is at factory setting on unleaded fuel, that is too much advance and is a contributory factor to overheating.

As my car runs cool (at times too cool), even though I accept that the plastic fan has performance benefits, I don't need them. But given the likely fatigue in the old fan, I may replace it - but with an original specification repro, mainly because with the Judson spacing is critical and there is only 1/8 inch between the fan tips and pulleys
dominic clancy

Dominic.....my new 7 blade plastic arrived yesterday and I measured it up. I also dug into my spares pit and found the fan spacer sent by George Folchi and not used to date. I checked all dimensions again last night and it should fit my Judson set up and today will start ..and hopefully complete both fan install and heater hose install. Re fan
....I will need to use spacer
.....I will need to get the radiator out and reset it away 1cm as you mentioned...and get it square .
Will tell you how it goes.

Two queries you can help me with..
.... How do you disconnect the lower radiator hose to get the radiator out . It is shrouded by the Judson pulleys ?
..... The heater hose take off point is just under the Judson jockey wheel ....does the heater hose/ pipe take off clear it ?
Neil Ferguson

So have you decided to go with just the Moss 7-blade fan on its own or are you using it in conjunction with your twin 8" electric fans Neil?

I have just taken delivery of a new Thermatic switch from Davies Craig that has a much better range (hysteresis)of 5 degrees C (9 degrees F).

So my twin fans should now be able to switch on at 204 degrees F and off again at 195 which should be ideal for my set up.
My engine only ever gets hotter than 195 when it is standing in traffic and so basically, the fans hardly ever come on. ( I have no engine driven fan)
I havent fitted the switch yet but I have high hopes for it. I will let you know how it works out in the spring when the car is back on the road.

Colyn
c firth

Colin...I am grossly overdoing the cooling..keeping the twin electric on therm. control, fitted them with thermo override bypass JIC, fitting a new 7 blade plastic fan .... I even have bilge fans in ducts on both sides of the radiator ( one for cockpit air, one for judson su carb air ).
The car will be sucking itself forward.
Belt, braces and elastic side inserts in my trousers as I get older ..trousers have been engineered ( and told) not to fall down.
Good to hear about the improved thermo switch....await news ...
Neil Ferguson

Dominic..this is a pic of the new fan with the 1.25cm Folchi spacer behind it ...it clears the jockey pulley by about 2mm so it will fit with the radiator moved forward as per the steel fan.. The leading edges do not protrude fowarrds ( camera illusion ) . The leading edges are flat.
Colyn..have done what you suggested ( on other post ) re the override for electric fans .


Neil Ferguson

Dominic..this is a pic of the new fan with the 1.25cm Folchi spacer behind it ...it clears the jockey pulley by about 2mm so it will fit with the radiator moved forward as per the steel fan.. The leading edges due not protrude fowarrds ( camera illusion ) . The leading edges are flat.
Colyn..have done what you suggested ( on other post ) re the override for electric fans .


Neil Ferguson

Neil, I had to smile when I clicked on the Image button and I had to agree with the button that pops up at the bottom left of the picture saying "Close". I would have said "Very Close"! :-)

Also, I just had this image of you stopping at the roadside, switching on all of your fans and doing a re enactment of the subway street vent scene with a Marilyn Munroe look-a-like standing next to the car! I think it was in "7 year itch" but it would have been perfect for this topic if it had been "Some like it hot!"

Sounds like a plan!

Seriously though, I would think that the 7-blade fan will do most of the cooling that you need and you will probably manage to get away with using just a single extra electric cooling fan on very hot days.

Colyn
c firth

Colyn....someone ( was it thou?) mentioned that a little in situ plastic matching could possibly help...if they touch ....but 2mm is a huge gap!
I should have the radiator back in today or tomorrow and I have an under bonnet electronic thermos so will be able to measure what the gale force winds achieve in a few days. Personally I like to keep the water very hot ( 190 to 200) and the under bonnet air temps low ..... I have
Neil Ferguson

Looking forward to seeing how it all works out Neil,
best of luck with all themods.

Colyn
c firth

...my last post ..insert 'machining' instead of 'matching ...
Neil Ferguson

Neil, Would like to talk again please contact:

bazangill@gmail.com

Thanks, Barry
Barry Gannon

The heater takeoff hose is trapped in place away from the idler pulley by the support strut that goes from the front Judson cover to the thermostat housing stud.

I usually fit the Judson last, complete with carb, so it is easy to get at all the other stuff. The only fiddle is getting the belt on, but here I also have a mod. I use an MGB harmonic damper pulley and a single V pulley on the Judson, so I have only one drive belt not two. tHis makes fitting the belt much easier, and the crank pulley helps prevent crank failure at the first big end.

If the radiator is already in and you can move it forward without disconnecting hoses, I would slot the holes in the mounting flanges with the radiator still hanging in place but unbolted from the flanges.

The radiator will not work any differently for being a few mm askew....
dominic clancy

This thread was discussed between 19/01/2016 and 05/02/2016

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