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MG TD TF 1500 - CARBURETTOR HEAT SHIELD

Can anybody supply a diagram for a heat shield .I have 52 TD that is showing percolation problems. It is hard to start after it is shut down and left for 15-20 minutes. When it starts it runs very rough until surplus fuel is cleaned out and then runs perfectly till the next shut down. It is definitely a heat sink problem and not ignition.
Sandy
Sandy Sanders

Here's how mine looks. Very simple and works like a charm. NEVER any over heating!

Dick Thomas
TD13583


Dick Thomas

Sandy,
Check the archives,
K seem to remember at least one reference to a diagram and also to someone who was makes a heat shield for the TD.
Sorry I can' be more specific, the age showssometimes.
Don

Don Harmer

Hi Sandy,

I would suggest advancing the static ignition by around 4mm on the circumference of the crankshaft pulley - it works well for my TF, engine runs much cooler. Also check out distributor bob-weight springs, and ensure advance matches revs. Heat shield helps as well but why MG suggested TDC for static timing goodness only knows! Even contemporary Morris Minor saloons were 4-5 degrees BTDC!

Cheers, John.
J.C Mitchell

I recently had the distributor for our TD rebuilt and am running with at least 5° of initial advance on it and while it has made the engine run considerably cooler, today on a run of over 100 miles in 90°F+ temperature, over some rather hilly terrain, I was running the temperature right up to 100°C on the temperature gauge and even with a heat shield in place, was experiencing vapor lock each time we stopped right along with the 5 other T series cars on the run. The situation with vapor lock has gotten progressively worse in recent years with the reformulation of the fuels we use. Since the problem seems to be the vaporization of the fuel in the passage between the float bowl and the jet in the carburetor. This bubble of vapor is trapped in that passage, pushing the float hard against the needle valve and stopping any additional fuel from getting into the float bowl and the engine, upon being started, is starved for fuel until the bubble of vapor can be cleared. Pushing the tickler pin will often upset the equilibrium and clear the bubble. If that doesn't work or if you just want to deal with it from the cockpit, just pull the choke out. You may have to run with it out for a bit to get everything settled down, but I am finding that it works quite well.

Sandy - I got your e-mail and will send you the info on the heat shield. Cheers - Dave
David DuBois

David,

I agree with your comments about modern fuels making overheating worse. Even with older leaded fuel, in the 70s my then TD was prone to vapourising during short stops for fuel etc and in the UK we don't get the very high temps. you experience.

Sandy, if you tackle the problem in different ways, as suggested in the Archives, I'm sure you'll improve matters considerably, except in the most extreme conditions.

Good luck, John.
J.C Mitchell

Sandy
years ago I fitted a fuel pump isolating switch as part of an anti-theft system. Since I changed to unleaded petrol I switch it off before I stop the engine. Since doing this I have had no problems with hot start up.
Ray
TF 2884
Ray Lee

Sandy,
I got over my senior moment and found Dave DuBois heat shield article.

It can be found at: http://homepages.donobi.net/sufuelpumps/ and select other Tech Articles.

In the meantime I see above that Dave has e-mailed you about his article.

Way to go Dave

Don H
Don Harmer

Ray - Good idea to defeat the vapor lock problem - no fuel in the float bowl/passage, no vapor lock. I too, installed a fuel cut off switch (actually used the unused fog lamp switch), but quit using it after our son was taking the TD to his senior prom and I had the switch off. The car died on him after getting out of the drive way and the look on his face as he walked back up the walk to the house was enough to make me never use the switch again. Besides, the flyoff hand brake is a better anti theft device anyway, but I may have to go back to using the switch as an anti vapor lock device. Cheers - Dave
David DuBois

I am convinced, together with SU specialist Don Jackson, that a carburettor heat shield makes the problem worse. What you need instead is a shield that deviates the heat from the fan which reaches the carburettors. I have temperature sensor on both carburettors and the front one is always about 4C warmer than the rear one, which indicated heat does not come from the outlet manifold but from the fan.

I may have described this before since praising the heat shield is a common mistake.

Denis, 1950 MG
Denis L. Baggi

Denis.. My problem is caused by heat sink after the engine is shut down and left to rest for 20 minutes. Continuos running never gives a problem.At 89 degrees F today it never missed a beat till it was turned off and left to rest for 25 minutes. This leads me to believe that the heat is coming up from the exhaust area and not the radiator.
Sandy Sanders
Hudson Florida
Sandy Sanders

I agree with Sandy. Yesterday was 94 degrees in Seattle (everyone up here thought we were going to die!) and on our drive, where I ran the temperature up beyond 100°C when going up some long climbs on I5 while maintaining 60 MPH and the car never missed a beat, but 5 minutes with the engine off or even 10 minutes of sitting still and idling and the car would vapor lock. If, on the other hand, I opened the right side of the bonnet while the car was sitting, there was no problem. Whether the heat is coming from the exhaust or the engine or both, it is heat soak that is causing the problem in my estimation. Find a way to remove the heat from the engine compartment or a way to prevent the fuel in the float bowl or the passage from the float bowl and the jets in the carburetors from vaporizing in a high heat environment and the problem will be solved.

Denis, I have to agree with you regarding the apparent uselessness of the heat shield, since I have a heat shield on our car and the other five cars with us had no heat shield and there was no difference in the occurrence of vapor lock in any of the six cars. Neither did any of the cars experience vapor lock while driving, only when the cars were stopped.

I have seen reports of cars not being bothered by vapor lock in which the exhaust manifold has had a Jet Hot coating applied inside and out. The reasoning is that the Jet Hot coating moves the exhaust gases through the manifold fast enough that there is not as much heat transfer as in an untreated manifold. I'm not sure that I buy into that explanation and having not seen a car that has had the manifold treated so I have no first hand knowledge that this, in fact, works. Cheers - Dave
David DuBois

After fitting a five speed box to my TD with the resulting repositioning of the engine about 10mm forward I installed a 'suck' electric fan to replace the blades connected to the water pump.
However, the new engine position meant that I was unable to install the new fan in the middle of the rad since to do so meant that I couldn't get the fan belt between the water pump and the fan.
So I offset the fan to the right. This has the effect of blowing 'colder' air across the front carb in particular, and the exhaust manifold.
Sitting in the car in traffic and putting my hand by the running board, the amount of hot air blown through the side louvres because of the position of the fan is considerable. The result is that in stop-go traffic or just idling, I have no problems with vapour lock.
What works for me to avoid the lock when parked is to pull out the choke and leave it out when parked, and then to turn on the ignition just prior to closing the choke and starting the engine so that the pump primes.

Mike.
Mike Christie

Mike - "What works for me to avoid the lock when parked is to pull out the choke and leave it out when parked, and then to turn on the ignition just prior to closing the choke and starting the engine so that the pump primes. "

It's interesting that clearing or avoiding vapor lock when the car is stopped always seems to involve the choke. I will give your method a try when we get some more hot weather here. We have gone from 90+°F on Saturday to mid 60°F on Monday - spring time in the Pacific Northwest. Cheers - Dave
David DuBois

Now I thank everybody for the comments and I have to admit that I am not going to be too scientific about it. Temperatures in Lugano in the Summer run above 90F and I never had vapor lock. My belief is that this occurs if you try to crank up the car you have just driven when it's hot, and then the front carburettor gets blown with all the heat from the radiator. If that is the case, install a shield between the radiator and the front carburettor. As stated above, I can prove the front one is warmer than the rear, because I have a digital thermometer connected to both.

I trusted Don Jackson on that, please do read his booklet "My SU Companion" published by the Octagon Car Club, he worked decades for SU.
Denis L. Baggi

Denis - Is the booklet by Don Jackson still available? I would be interested in reading it. Also, what is the altitude where you live? I remember as a child back in the 50s, living with my grandparents who had a summer cabin in the mountains at 3000ft altitude. Their main home was down at sea level and it seemed that there was always more of a problem with the cars vapor locking at the higher altitude, probably due to the depressed boiling point of liquids at higher altitudes. Cheers - Dave
David DuBois

Hi Dave. That booklet was sold by the Octagon Car Club and I am not sure it is still available. It is a source of info about SU carbs and fuel pumps, however the info on the shield was given to me by Don in a letter, he sent me kindly various parts to rebuild my carbs. He was very kind and had a TF on which he mounted 1 1/4" carbs.

If you are truly interested I'd be glad to copy it for you, and send it by snail mail - my university will pay!

I live at about 270 m above sea level, so that this is not an option, I do not see any difference when I go down to sea level.

Denis
Denis L. Baggi

Denis - If you would e-mail me at the address above, I'll send you my postal address, I would very much like to have a copy of the booklet.

270m above sea level shouldn't make much of a difference although it would be around 3.5°F - 4.0°F in the boiling point of water. At 3000 feet and above, there would be a significant difference. Cheers - Dave
David DuBois

David,
I had my manifold jet-hot coated over the winter in hopes of avoiding the vapor lock...last week it was 95 degrees in Boise and I was doing very well up the hills...kept @ 90C while last year without the jet-hot coating it would be @ 100C...unfortunatly...the vapor lock after shutting down has not stopped...still runs ragged after a 10 minute stop...I'll try the choke...also think I'll put in a cut-off...that seems the best...no fuel in the bowl...no vapor lock...
Bob Doc
R Dougherty

Bob - Thank you for the information. I rather suspected that your experience would be the result of the jet hot coating. I found on our outing last weekend, that propping the hood open on the carburetor side of the engine eliminated the vapor lock when stopped. Cheers - Dave
David DuBois

My friend's '51 TD is exhibiting "vapor lock" and I'm trying to help him (blind leading the blind?). Dave's link above returns an error404 "URL not found." Does anyone know if the wealth of information that was on Dave's site is available elsewhere? Thanks.

Jud
J. K. Chapin

As a test you could wrap the float bowls with home pipe insulation held on by zip ties. Easily removable and may definitively determine your problem. I also covered my metal fuel line to the pump with rubber hose so it does not absorb as much engine compartment heat.
John Quilter (TD8986)

Reading Dave Dubois’ past contributions today made me pause for a moment. As evidence, his presence will continue to be a part of this forum for years to come. RIP
W A Chasser

I got mine from Barry in the UK. Hard to photograph as it's so shiny, made from stainless. For extra protection, I put heat shield material on the back. PJ



PJ Jennings

Tell your friend to just use the choke. Works every time. No mods to the car.

Other than using the choke when restarting a hot engine, only propping the hood open or installing a thermostatically controlled electric cooling fan wil give relief as any heat shield, wrapping of components, etc is fruitless as everything under the hood will be the same temperature. It is ALL heat soaked.

Just pulling the choke on works every time to restart.

Regards, Tom
tm peterson

The hot restart problem is caused by fuel in the jet evaporating as there is usually one inlet valve open with a stopped engine that allows heat to escape back up the inlet manifold to the carbs. Modern 5% ethanol dosed fuels will start to evaporate at temperatures well below those usually found under the bonnet (hood). Heat shields are ok and will help on a hot day whilst running but not stationary. Solutions are a) use (in UK) RON 97 super grade fuel such as Shell V-Power and b) some choke briefly whilst restarting the engine. I also set advance at 8 - 9 degrees BTDC (TF1500) static and tickover, using a CSI programmable electronic distributor.
N D Wallace

Jud -

I have the heat shield / vapor lock article by Dave Dubois.

Email me so that I can capture your email address and send PDF to you.

Lonnie
TF7211
LM Cook

My experience is that a heat shield is of little use during long periods in very slow moving traffic in hot Florida weather. The under-bonnet temperature soars and everything becomes heat-soaked under the bonnet. A heat shield won’t help under these conditions. I am toying with the idea of adding louvres to the top of the bonnet to allow the under-bonnet heat buildup to escape. There isn’t sufficient airflow to remove the heat when idling in long lines of traffic.

I once read that the original model developed for manufacturing approval had louvres along the top of the bonnet. They were removed from the production cars. When I look at Morgans and many older, exotic sports cars, they have louvres along the top of the bonnet. I think they are there for a reason, not just for cosmetic appeal.

Strangely, even when I stop for gas and my temperature gage registers 205 Deg. F due to a thermo-syphoning effect, I never have a problem to restart.

Anyone have any thoughts concerning the benefit of louvres along the top of the bonnet, other than stuck in traffic in a typical Florida hot afternoon thunderstorm accompanied by torrential rain?

Unfortunately my approach is to keep mgtf standard, no blingy stuff or modifications. I am looking for a spare half bonnet to see how the louvre approach works. Anyone have a surplus half bonnet they wish to sell?
TF 1500 9194

Fit a 7 blade fan from an MGB and it will assist.
Dave H
Dave Hill

My brother, who had several TC's & maybe TD's back in the late -50's early -60's had louvers in the bonnet tops on one of his cars, and I remember him saying it was a great difference for the good.
YMMV
Al
54 TG TF "Emma"
Al Parker

I designed a heat shield for the TF using CAD i.e cardboard aided design. I simply removed the carbs and made a template out of a cornflake box. I then spent a very pleasant hour with a sheet of aluminum, a hacksaw, a drill and various files to make up a heat shield. Fuel vapourisation has never been a problem.


Jan T
J Targosz

Here is my heatshield.
Good points of my design are
- No additionnal leak point at the carb flange
- Air deflection for the front bowl
- Easy access to carbs once installed
- Global protection for the whole exhaust manifold

And weak point is :
Very tricky fitting at the bottom of the exhaust manifold

Mine is made out of a 1.8mm thick stainless steel sheet. Thinner would produce vibration as it has only two fixation points
Dotted lines are places where the sheet needs to be folded.
The big square part on the right needs to be adjusted around the front bowl, 1 cm distant approximately.
Inner part of the sheet is covered with a high insulating material sheet for exhaust.

The down pipe is also wrapped with insulated strip and I installed insulating spacers between the carb flanges and the inlet manifold.

Very good results with my stage II engine up to 37°C ambiant air temperature. Maybe 5°C more but not tested.

Laurent.



LC Laurent31

Dear all, I have a heat shield on my YT that I found on the "mini-mania" website. It is available for the dual SU's. Sorry, I don't have the part number as I am not in the garage. Tom
Thomas McNamara

I have a spare bonnet set for a TF and have been looking for someone in our area to put louvers in them, but all the guys that did it in the past are gone. I was even thinking of buying a set of dies as I have a press, but don't think I want to go that route. Don't want to ship them to California! PJ
PJ Jennings

I actually don't have a fuel problem and I believe it's because I use nothing but non-ethanol fuel, which were lucky enough to have an abundant supply here. I do use 87 octane and the car runs great. I tried a higher octane and it made no difference in performance. PJ
PJ Jennings

I have never known a properly stage I tuned TD/TF to experience any vapor lock issues while running. I drive all the time in 100 plus temps in stop and go traffic..once famously for over 2 1/2 hrs , with NO vapor lock. (Now when you make a short stop that is another story..but heat shields are no help nor is a multi blade fan..but the use of the choke to start works every time in that circumstance)
The multi blade fan will only have an effect during extensive operation in slow traffic...if you are moving at speeds more than 20 mph the car speed will provide the cooling airflow.
Before you switch to a rain catching louvered bonnet piece, make sure your car is in proper tune, the radiator is not blocked inside or out and check for dragging brakes.
Just my 20 plus years driving TD’s.

Regards, Tom
tm peterson

This thread was discussed between 17/05/2008 and 10/04/2019

MG TD TF 1500 index

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