MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Do I need to buy a new carb heat shield?

Hi,
I took my carbs off to get the throttle bushings replaced by Joe Curto and I noticed that my carb heat shield is missing insulation on one side. Do you think I should just buy a whole new heat shield? Or is there something else I can use in its place? What have some of you done to replace or increase the insulation on that shield? Thanks.

Alex
Alex

When I bought my car, four years ago, the heat shield was present but had no insulation whatsoever. I've never had a problem with vapor lock, so I haven't given much thought to replacing the insulation.

I suspect that the uninsulated heat shield performs at 90 percent of the efficiency of the insulated one. I say this because, it seems to me, that the primary funtion of the shield is to divert hot air rising from the exhaust manifold around the carburetors. My uninsulated shield still does this.

The insulation would reduce the amount of heat absorbed by the shield itself. This heat would then be re-radiated upwards toward the carburetors. I don't have this protection, but I think that the very hot air from the exhaust is much more of a problem than re-radiated heat from the shield.

The original insulation was asbestos, so it may have been for fire prevention as much as anything, to limit the spread of a fire from the exhaust manifold to the fuel system and carbs.

Search the archives. There have been several discussions about this over the years. One suggestion was to get some heat insulation used by racers. Another was to use a thin sheet of aluminum, almost a foil and rivet it to the underside of the heat shield with standoffs to create an airspace.
Paul Noble

My heat shield is in the same shape. The insulation is missing on one side. I had a little bit of a vapor lock problem last summer when it was extremely hot out, so I'll be looking to both shine up the heat shield (so it reflects heat better) and replace the insulation.

There are substances out there you can use, I just can't remember what they are!
Kim de B

I used something similar to this when making a new heatshield:

http://www.jcwhitney.com/product.jhtml?CATID=176054&BQ=jcw2

The stuff I used actually came from a local hot rod shop. The adhesive seemed OK, but not great. Aa few 1/8” pop rivets with washers around the edges seemed to make a secure arrangement.

dlw
David Wagner

I had a similar problem with my '72B. I bought a piece of insulating fabric in the plumbing department of the local Home Depot. It is used to protect walls behind pipes being soldered. It costs about $15. There is enough fabric to insulate the entire back of the heat shield, including the middle and the bottom where there was no insulating material originally. I used pop rivets to hold it on.
glq Greg

Alex. I asked a similar question several weeks ago and there was a recent question on this on the MGA board. The best solution I have seen is the Home Depot insulation using pop rivets and a washer on the end opposite the large end of the pop rivet. I used the "cut to size" insulation from a speed shop and held it in place with machine screws, washers and nuts. However, this was with an aluminum covered, fiberglass insulation. For my next one, I intend to try the Home Depot insulation/pop rivet system as it sounds to be better.

My heat shields were cracked as well as insulation being missing. A good welder took care of the cracks for me. I then bead blasted the heat shields, sprayed them with silver "header paint" and attached the insulation. Do not know exactly what difference it made because I also installed a Peco "Big Bore" exhaust system and 3" K&N filters at the same time. (This is why I noticed the heat shield condition.) For an old and tired engine, it sure runs very well. Les
Les Bengtson

This is not intended as an anti- American statement, no is it sick black humour, but I did wonder, long before the space shuttle disaster, just what those tiles were, where they might be obtained, and if they might be used on the back of a heat shield. I decided that they were probably not available to us and so I considered using ceramic tiles from a home centre, and drilling and bolting on. Has this been tried?
Ken R
Ken Rich

Alex-
If you live in or near New York City, then you know how high underhood temperatures can be when sitting in stalled traffic on the Long Island Expressway in early August. Heat from the exhaust manifold can percolate the fuel in the floatbowls and stall the engine. Of course, the car will refuse to restart until it cools off, so you'll have to push it out of the middle lane! This actually happened to #4 Son's 1973 Roadster. It's a miracle that a trucker (from The Southland) blocked the lane so that he could push it to the side. Any local speed shop should be able to supply you with insulating material and the high temperature adhesive to glue it on. Do it now before the weather turns hot.
Steve S.

Uh, yeah, no kidding the space shuttle tiles are available. They're about $1,000 a piece or something... And they're made from a special silicone susbtance.

You are kidding about using ceramic floor tiles, right? Besides being fragile and not at all heat resistant, they would do absolutely nothing to shield your carbs.

Ever wonder why, on a cold morning, the tile floor in your bathroom feels a lot colder than the throw rug on the floor? It's because ceramic floor tile is lousy at reflecting heat. It just sucks it up out of your feet. They are basically just made from clay. (The tiles, not your feet!)
Kim de B

OK Kim, thanks for the physics lesson. Guess I thought a highly glazed surface would reflect heat. As for strength, they'd pass, if bolted to the steel. Then what about a small panel of asbestos cement sheet- called "Fibro" in AUS, and once used to build houses. About 3/16" thick, and it can be cut and broken along scribed lines, and drilled quite easily- of course, it is asbestos, unfortunately, and that is something one should be trying to avoid.
Ken R
Ken Rich

a tile of asbestos cement..that's what I used on my car..and it works great..as you said, you cut it very easily..

JF
JF

Jumpin' Jesus on a pogo stick!....The original heatshield insulation is asbestos based, if it fell off good friggin' riddance! The last thing you want to be doing is dicking around with your old heatshield if the stuff from the factory is still there. The most inane people you will ever meet wire brush the old insulation off so they can paint the heatshield, wearing no PPE the whole time. Lots of other cars have similar heatshield with no insulation, of course they have comparatively fat assed emulsion blocks. If you're heatshield ain't cracked, but doesn't have the insulation, it's ok, just keep on using it.....Ahem these cars can vapourlock for a variety of reasons....and if yours is vaporlocking noticeably, it's more than some missing inulation causing it.

If you're heatshield is cracked and crap, why go welding on it???....The metal cracked because it had become embrittled from the heat. If the thing has become all bagged out from years of heat cycling the metal, don't be dense, just buy a new one. If the new one may happen to be cheap Chinese crap, not to worry it holds up as good as the original does and has a nomex weave similar to the home depot insulation you dudes are using, but it's a bit thicker. Even the "crappy Chinese" one is better than an old repaired shield.
And yes Virginia there's still a Santa Claus, and if you're a good boy or girl he can get you a brand spanking new old stock one complete with the original toxicity Concours judges love. You just gotta look.
But why put asbestos back on the car...you're just making a market for deadly fiber. Next you'll be wanting to eat Grape Nuts cereal...grapes don't have nuts, but the stuff is like razorblades for your large intestines yaknow.....And asbestos is like cement to close off your aveioli. If you feel the need to damage your lungs so severely, take up smoking.

If you're like me, you're time=money. Even if you're not like me your time can be better spent screwing your wife or getting drunk as opposed to playing heatshield doctor. If it's missing insulation and it's not 102 in the shade, forget about it. If it starts to crack, replace it.

If you're really bored, machine up some sw*nky finned brass emulsion blocks with cool recessed O-rings instead of paper gaskets. Then run no heatshield, just a cool little spring tab that runs between the two blocks to hook the throttle springs. Yeah look at the old MG Buyer's Guide at the picture of serious performance parts available for special tuning......That's right Poindexter, a lot of the special tuners ran no friggin' heatshield.... It's not too tough to keep the carbs cool, put that accelerater pedal down harder and drive faster! The trick is keeping the damn things warm enough to work off the coke when it turns cold out on you.

And now a word on space shuttle tiles....
When we say ceramic...as in a ceramic engineer...we're talking about a specialized composite, not the tiles and pottery crapola done in a kiln. This specialized silica containing composite is made in the autoclave.....Not an autoclave for sterilizing the crap outta surgical instruments, but a pressure vessel that maintains a high temperature and a high vacum to produce a void free composite.

They're not made from a silicone substance you doof. The prepreg has silica fibers in it. Because of the water absorbing charachteristics of the open hydroxyl groups present in this material, they'll bond with hydrogen and therefore suck up that ever dangerous hydrogen hydroxide. To keep that from happening "the man" introduces the hydrophobic silicon component onto the finished tile. This is not at all like the silicone found in your wifey's surgically enhanced happysacks. The alkyl silane is a waterproofing agent applied to the tile. The tile isn't actually made from it. As I've said Dihydrogen-Monoxide needs to be repelled at all costs...it's killed a lot of people. But there's more than one type of tile, let's look at my favorite tile the RCC.
RCC or reinforced Carbon-Carbon composite is the mad note baby! But LEO the Lion will go GER, and the damn schtuff gives up those outter electrons above 800 degrees like a two holed whore on payday. To stave that whoreish oxidation practice off engineers coat that sorta tile with a silicon carbide oxygen barrier coating. That still isn't your wife's breast implant silicone. It's leading edge type stuff.

I do not expect many of you to grasp the subtle art that is advanced materials engineering. But, for those select few with the required predisposition, I can teach you to bottle fame, brew glory, and put a stopper in death....screw that! When you know how to make space shuttle tiles you realize space shuttles suck but lightweight ultimate supercars are where it's at.

James H.

James. Nice to see you back. Many find your posts quite amusing. As I read your post, the information value is that you, as a professional mechanic, make more money by selling someone a new heat shield than by recommending they refurbish their existing heat shield. I agree completely. A professional mechanic should be able to make more money by selling a new heatshield than advising an enthusiast to rebuild their existing heat shield. Les
Les Bengtson

As a professional mechanic, I'd make more money putting the carbs on with a crappy heatshield, then taking them off again at a later date down the road to reinstall them again with the new heatshield in place when the old cracked one failed completely and let the throttle return springs and such go flying away.

Since I always provide the new parts at my cost and make all the money I earn off the hourly labor...I actually make less money by installing and recomending a new heatshield.

The value of your last post is that you lack the reading comprehension skills to glean the important facts....
1. If the heatshield has lost it's insulation but isn't cracked, you generally don't need to waste your time screwing with it.
2. If the heatshield has cracked you should replace it with a new one.
3. If you act like Les and wire brush it (or bead blast it outside of a cabinet...and yes Les most others will use the wire brush instead of the blast cabinet you did), handle it, repaint it, or otherwise dick around with it, chances are you're going to inhale a good portion of asbestos fiber that could lead to severe health problems later.

Now Les, a professional mechanic should be responsible for the health and safety of the amatuer enthusiasts he advises before turning their concerns to making money...So as a professional mechanic I want the amatuer to handle their old heatshield (if it's an original item) as little as possible if it all.

Gee Les for your next trick are you going to tell people you snort dust off the original brake linings too?
Maybe you want them to work under the car without jackstands?....Stare at the pretty bright light with the unaided eye as they mig weld?


Well Miz there's a venomous whore on this BBS, but it ain't you!
James H.

I see that James has been brewing. A voice from the past, a breeze that carries with it memories and amusement. Glad you post again, James, and seem to believe it is still a free country (or BBS - anymore, who knows?)
Bob Muenchausen

Ah, James! If only we could convince you to head west . . . we need someone here with your skills. First of all, to care for our MG's.

But then, perhaps you could run for governor. We need someone who knows which end the bullsh*t come from!
Dan

James. It at least we agree that Stef is not, in your terms, "a venomous whore". I wonder why you should think that she is. My impression, formed from reading her postings on "Horizon", is of a very strong woman who was raising a child on her own. I have, from time to time, had to be a single parent when my wife went off to fight small wars. While I knew she would be back, the task or raising young girl children is, at best, somewhat daunting. Thus, I would drop down to Horizon and read Stef's posts. After reading them, I would leave severely humbled and dedicated to doing better in my own life. Stef was in inspiration. It provided me the greatest sense of joy when she and Mike/Dai got together. One can only hope that each realizes what a unique person they each would up with. Mike leaving Wales (such as Prince Modoc--Mike--did I get that name exactly right?) did to move to the "new world" and form a new life. While Stef agreed to accept this "stranger from a strange land" as her beloved. Shades of the old "mail order brides". One can only admire the courage both have shown in this endeavor and can only hope, most fervorently, that their union has been a splendid success. If for nothing but their daring, they most deservedly, should benefit from the joy of success.

For you to suggest otherwise would be a dis-service. If you have a problem with me, take it out man to man. But, do not bring up Stef's name in such an endevor. Les
Les Bengtson

Les.

:-)

Any chance we will get to meet you at Sinfest2003 (MG2003 for the staid fogeys. :-) )?
The Wiz

Mike. It would be both a pleasure and an honor, but, most likely I will not be able to get free to attend. But, someday I will manage to get back east and see what has changed over the years. Les
Les Bengtson

Hmmm, James H., from Iowa, eh? Giving us a dissertation on thermal properties of exotic materials!?! James, I'd have to guess you copied all that crap from a website or some book, since you obviously don't know much about thermal characteristics of COMMON materials, let alone exotic ones. Folks, this guy shipped me an overdrive transmission from FROZEN frikkin' IOWA in DECEMBER in a frikkin' RUBBERMAID TUB!!!! Of course, when I got it, the tub had frozen, the input shaft had cracked out about 75% of one end of the tub. To make matters worse, he had removed the inspection plate and the front seal cover, and left them and their hardware in the bottom of the tub. Without the seal cover on, the layshaft was free to slide out and drop all its parts into the transmission, then continue its travels out onto the floor of the UPS truck to join all the other hardware and pieces. I wouldn't listen to anyone rambling on about shuttle tiles if he doesn't realize that PLASTIC GETS BRITTLE WHEN IT GETS COLD!!!!!
Ken Lessig

All things old are new again! LOL
Bob Muenchausen

I replaced the heat shield insulation with a piece of flat gasket stock about .12" thick. That was about 8 years ago and it still looks good. You can get flat gasket sheet stock at any industrial supply house. I used some high temp stuff we had here.

Jim
Kalamazoo
Jim Budrow

Contrary to what James Hesser says, I welded up a cracked heat shield almost 15 years ago, and it has been on my 68 B since 1989 and it hasn't cracked again yet . . . anywhere. Doesn't mean it isn't brittle or even more brittle than it was. But I sometimes think we get just a wee bit too dogmatic about what we know vs. the realities of life as it so happens.

Perhaps the wild card in this hand is that at the same time as I welded up the crack, I also applied a replacement sheet of non asbestos containing heat sheild material from the local hot rod shop (a tough but somewhat flexible sheet about 1/16" thick), and between that and the manifold itself, an aluminum reflector made from the metal sheet used in, of all things, one of those disposable cookie sheets you might find in the cookware section of the local market. None of this was rocket science, and none of it terribly exotic. The proof of the pudding is in the eating, and for the empirical part of the equation, this has seemed to work just fine and lasted all these years. And I would bet there are another 49 ways to keep the heat at bay.
Bob Muenchausen

This thread was discussed between 25/04/2003 and 01/05/2003

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.