MGB & GT Forum

On this other thread a request was made for the dimensions of the original Mud Shield that came on these cars. New ABS replacements are made (Moss #458-195, which is NLA, or it's replacement Moss #458-194), but some of us like to fabricate our own. Since I made mine 17 years ago, and still have the template I used, I promised to post a measured drawing in case anyone wants to use it. The result is the pdf version attached. I chose that format so a user could zoom in to decipher my notes. I apologize in advance for my terrible handwriting....I apparently acquired that gene from my Dad.

One thing to keep in mind.....these dimensions may need tweaking to fit your car. I made a template out of foam board (like you use to mount posters) back then based on an old, very poor condition original - so very accurate measurements weren't possible 17 years ago....and still aren't. Do what I did.....make yourself a corrugated cardboard template (that's what Amazon boxes are good for), fit that to you car and adjust as required before transferring those templates to your desired material.

I used .025" aluminum from Lowe's because it was readily available, cheap, rustproof and very easy to work with - so special tools or skills required. You may prefer a different material and have the skill set required.

Good luck....and have fun!

Joe,

I have an '80 MGB in very nice, mostly original condition. The 'mud shield' is original and in OK shape but I think that it's ugly and I question what function this part serves as none of my American built vehicles have ever had such a feature. In the factory configuration, with the electric pusher fans, I suppose that there may be some improved cooling with the shield in place. Since my car will strictly be a fair weather cruiser, I don't see any value in having a mud shield which would rarely, if ever, get wet.

I'm planning a make over of the cooling system this coming season and will flush the cooling system thoroughly, then remove the radiator for additional flushing and inspection. The twin fans will be retired and I have a new 13 in. puller Spal electric fan to be mounted to the back of the radiator. I'm also considering use of the Clark & Clark molded shroud and I would modify it to allow securement of the Spal fan. One issue I've discovered is that the front sway bar is located near and close to the bottom of the radiator, so there might be some more 'tweaking of the shroud there. With these modifications to fan-forced cooling in place, I still don't see much, if any value, of the factory mud shield. I would just remove it for work on this project, then leave it out and add it to my stash of MGB parts..

Am I missing something?

Thanks for any comments you may have.

Good evening,
Richard

I guess the first question is why do you need to redo your cooling system by replacing the fans, adding the shroud, etc.? All that on my '78 is absolutely stock except for the thermostatic switch in the top tank. It was missing when I got the car and the hole was plugged....the fans ran all the time. I installed an aftermarket switch (Hayden, as I recall) so the fans would cycle on and off as they should. The car has never overheated in the 23 years I've owned it.....never even come close even in traffic in the hottest weather.

As for the mud shield, I seriously doubt it has any affect on cooling. I'm pretty sure that wasn't it's purpose. I had my car about 4 years before I fabricated and installed mine and I never saw any difference in cooling with or without it. I just think it adds a more finished look to the engine bay. In the "Production Changes" part of Clausager's book the part is called "mud and acoustic shield"...not just "mud shield." If it had been to somehow aid cooling I would imagine that terminology would have been included in the description. The "acoustic" part seems odd to me, but maybe it smooths out airflow under the car and reduces noise from turbulence? Again, I never noticed any difference.

I would think the main purpose of it is to protect the crankshaft pulley area from water, dirt and mud from splashing up through that big hole and onto that area - possibly causing belt slippage or damage. That may not be likely in the way most of us use these cars now but I can see it being possible back in the day when we drove them on any kind of roads, in any kind of weather.

If you don't want it I don't see any negative results from it's omission. On many cars it's been missing for years...

While my car is in very good condition I believe that the last owner didn't do much maintenance on it in the 19 years that he owned it. I think that the cooling system needs a good, thorough flush and who knows how plugged up the radiator and heater core are. Also, what little bit I was able to drive it last summer, it seemed to run pretty hot with the fans cycling quite a bit. To add to that, the measured amp draw on the fans seemed high to me at about 11.5 amps total for both fans and they didn't seem to spin freely by hand. I tried removing them for winter rebuild and was able to remove one without much difficulty. The other one, though, I messed up while trying to remove the yellow plastic fan to allow the motor to come out the front of the vehicle. That's why I decided to source and use a new puller electric fan.

As far as the mud shield, it will be easier to remove once the lower radiator hose is out of the way and I see no reason to not remove it while I'm involved in work on the front end of the car. The bolt head on the end of the crankshaft will be more accessible and I think that it will actually clean up the engine compartment without it and allow for easier inspection of the steering rack, etc.

I hope that this makes some sense even though you have other thoughts.

Richard

I think it's great that Joe has published the dimensions for fabricating this shield. I wish I had seen this 2 years ago when i was looking to replace the remains of the original shield on mine as there was not enough left of the original to work from. After some looking around I bought a ready made aftermarket one in stainless steel from a UK seller. As I see it the shield plays a part in smoothing the airflow under the front of the car and also protects the crankshaft pulley and belt etc from water, mud & stones thrown up from the road surface.
But the real reason I did it though is it just looks great in an RB car as a polished, shiny, floor to that very open looking area between the engine and radiator.

Was scrolling through some images on the laptop a couple of days ago and my dimension pictures were on here:

Richard,

My understanding of the need for the mud shield was twofold. First, it protected the engine bay and belts from road conditions and water, as others have stated here. Second, I was told that the shield prevented turbulent air from coming up into the engine compartment. This would prevent proper airflow from going through the radiator as it creates a high pressure zone directly behind the radiator.

The optimal configuration for the radiator would have the mud shield and lower air duct installed.

You wouldn't also happen to have dimensions for the lower air duct as well? I have been trying to hunt that down.

Regarding the need for a “mud shield”, Kelvin Dodd (Moss engineer) has this to say (post #8):

https://www.mgexp.com/forum/mgb-and-gt-forum.1/lower-air-duct-and-mud-shield-needed.4191706.4192614/#msg-4192614

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Pogo is right.
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“I did all the extra credit, then got graded on a curve.”

If anyone reads Kelvin’s remarks regarding the factory V8, he is mistaken. The V8 cars always had two cooling fans (like USA cars) and the oil cooler was always mounted on top of the duct panel.

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Law of Logical Argument - Anything is possible if you don't know what you are talking about.

"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."

Same goes for the MGB plastic starter motor cover.

Tony (post #6),

If I had a mud shield that looked as good as the one in your photos, I'd definitely use it. Since my mud shield is the original flat black fiberboard, albeit in good functional condition, it's looking pretty road worn and unsightly. Once I complete the maintenance and upgrades to my cooling this summer, I'll soon learn whether or not the absence of the mud shield impacts engine cooling in a negative sense. I'll report back to the forum at that time.

As usual, thanks for the information and advice.

Richard

Was just searching images on my phone again for something completely unrelated and found a picture sent to me by a friend who was rebuilding a B years ago and asked me to do him a guard that will finish off the engine bay nicely.