Further efforts to limit the effects of under bonnet temperature in a TC

Steve Priston described in Issue 56 (October 2019) his attempts to improve matters with hot fuel under the bonnet. This included re-routing the fuel hoses to the carburettors by swapping the float chamber tops over, enabling him to run the feed to the front float chamber around the back of the air cleaner, so that being nearer the bonnet louvres, it was away from being directly above the exhaust manifold. 

Regarding the fuel hoses themselves, he made some new hoses in 6mm bore, reducing the hose stored fuel volume, by around 40% per inch.

The fitting of a Facet fuel pump rendered the SU pump redundant with another small reduction in under-bonnet stored fuel.

As a further development he decided to try fitting pancake filters on the assumption that they would draw in cooler air than the standard arrangement, which being  situated at the highest point under the bonnet, would surely pull in the hottest air, rather than being as far away from the exhaust/engine heat, as you can get.

A pair of foam type pancake air filters, were purchased. Also sourced was a pair of replacement outer covers, in order to create the required offset hole to miss the radiator support strut.

“All in, having bought filter assemblies that were sold on eBay, as seconds, along with the two extra covers, the cost was £23. Yes, they are almost certainly made in China and yes, they needed a bit of finishing off, but they are stainless steel as well as being cheap!” said Steve. Having studied Brown & Gammons heat shield, along with one featured in a restoration book, that fitted to the manifold clamps, the heat shield you see in the picture below was fabricated using a piece of 3mm alloy.

Rather than resort to a cardboard template the inlet manifold was measured up (7 3/16” centres) and a SU gasket was used as a template.

Two spacers, made from Tufnol were cut from some 6mm material, with paper gaskets fitted between everything, and with the addition of ‘Wellseal’.

Steve is hoping that the front lower bend in the heat shield, will help direct an airflow, between the shield and the manifold, also that the alloy will help to dissipate heat, more effectively, than steel.

To fit the carburettors, it was necessary to use a couple of M10 studs for the lower fixings, due to the lack of room, preventing the fitting of a long enough bolt.

The carb to carb hose has been moved again, now being lower and about as far away from heat, as it is possible to get, being about the same length now, as the original.

All that is needed now, is to find a suitable breather, to screw into the rocker cover and for the weather to improve for road testing. The pancake filters make tuning of the carburettors much easier, with only a couple of 6mm nuts to undo on each. Steve has come up with an easy way to check/compare the air flows, which is to use a cheap (yes eBay!) stethoscope but not with anything other than the open, lower piece of tubing, held in the carburettor mouth, so a much clearer sound can be heard when listening for a difference in intake roar!

4 thoughts on “Further efforts to limit the effects of under bonnet temperature in a TC

  1. Steve Priston says:

    Please do not feel in any way that these modifications are necessary, if you are not experiencing any difficulties with the way your car is behaving, after all, everybody has a different driving style & certainly expects or hopes for different things from a car.

    I come from a classic/vintage motorcycling background & am a time served Mechanical Fitter so make reversible changes, realising that our current fuel situation is not going to get any easier for our vehicles to cope with.

    Also because for a large percentage of it’s use, my TC also carries my Wife as a passenger & having already been stranded on the side of a road for hours, waiting to be recovered, after the flexible hose to the oil pressure gauge ruptured, I am simply trying to avoid further embarrassment.

    As everything that I do, to try to improve the reliability of my car is reversible, unfortunately in many cases, it can only be a compromise.

    Like trying to keep the modern fuel cool, in a small engine bay, with a great lump of hot cast iron radiating heat, with only a vented cooling system & large radiator to cool things down.

    This article is actually incomplete because the weather, through it being winter at the time it was written, prevented any serious testing to see what improvement, if any, the new set-up had made, well I have now used the car for some reasonable distance runs, before our current “lock down”.

    After a return non-stop journey, of 25 miles, I could easily hold the carburettors in my bare hands, straight after pulling up on my drive.

    However the new alloy heat shield, I couldn’t & didn’t want get my hands near, as it had worked as hoped, like a heat sink, with the tufnol insulators, as effective as they are on my air cooled iron motorcycle engines.

    With bikes, you can turn off the fuel supply, with only a small amount after the tap, to evaporate & if a single cylinder job, leave the engine, with the valves closed.

    In two wheeled circles, we refer to the problems with modern volatile fuels, as “vapour lock”, however with a car because you have more cylinders than ancient bikes, you are likely to get the engine to eventually start & if you can keep it going any sense, will once moving, usually get things to calm down, when the cooling air through the radiator does it’s stuff.

    This will usually cause some interest from bystanders & quite likely some amusement, at your expense but there is obviously the chance that it might not happen, especially if you drink your coffee slow?

    Remember to keep your heads well below the parapet or the market could be flooded with classic vehicles next year!

    Oh, I forgot to mention, last year a friend & very clever colleague of mine phoned, almost in tears because he had seen what had happened to his 1927 Morris cylinder block, after realising that he had built his engine using a head gasket from a faulty batch but had been only using rain water as coolant!

    Happy tinkering.

  2. Chris Parkhurst says:

    I must have some magic under my bonnet as I have yet to experience problematic under bonnet temperatures on my unrestored TC !
    Those of you who know me will be aware that my TC is an everyday car travelling throughout the UK and France in all weathers. Last year in the summer 38c in France I still had no issues whatsoever. The secret ? When I rebuilt the engine 10 years ago I spent days Chipping the crude from the block and I found the magic hole behind the front core plug and reinstated that. Second a new radiator.
    Third correct radiator grill gaps.Fourth only water from the garden butt.No electric fan just the production metal fan.
    Plus I really drive my TC hard just as I did as in 1966 the more you thrash em the better they go !!


    • Alan Ballard says:

      Hi Chris, sounds like you’ve got the TC temp issues nailed. What’s the “magic hole” all about and will I have one on TD?

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