Big15 Fuel Grade / Gaskets
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Thread: Big15 Fuel Grade / Gaskets

  1. #1
    Tadpole
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    Default Big15 Fuel Grade / Gaskets

    My 11CV engine runs Lucas ignition and a Weber twin downdraught carburettor. I started on 91 with a cap of flashlube per fill but have switched to 95. Is 95 the way to go?

    I haven't found a tune yet due various issues / learning.

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    Latter leads into another question re gaskets. I had a leaking inlet manifold gasket which has diminshed after a half turn but it still needs replacement. I also have a leaking manifold to exhaust gasket. I have applied to join CCOA but have yet to be accepted. The question here is whether traction owners are generally sourcing such gaskets from CCOA or Franzoze or Jose Franssen or otherwise making them up themselves?

  2. #2
    Tadpole
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    Sorry that's a single downdraft Weber

  3. #3
    1000+ Posts gerrypro's Avatar
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    Manifold leaks can be corrected by having the manifold to head gasket face surface ground both the inlet and exhaust manifolds need to be in the same plane and be perfectly flat. Most engine reconditioners can perform this task. Another source of air leaks can be found around worn throttle spindles. This condition has its worst effects at idle speed.
    The next thing to look at is the condition of the centrifugal advance. This can be quite worn and cause an over-advance for higher rpms. Twisting the springs half a turn can restore the spring tension and tighten up the fly-weights.
    Also look at the vacuum advance capsule to see whether it is functioning properly, and giving the correct degree of correction for closed and open throttle.
    I run mine on 91 RON with a dash of flash lube. Runs well!
    Cheers Gerry

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    Too many posts! JohnW's Avatar
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    I've just faced up an inlet/exhaust manifold with a large mill bastard file. Takes a wee while but close enough for the gasket to take up the slack so to speak.
    jaahn likes this.
    JohnW

    Renault 4CV 1951
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  5. #5
    1000+ Posts gerrypro's Avatar
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    Quote Originally Posted by JohnW View Post
    I've just faced up an inlet/exhaust manifold with a large mill bastard file. Takes a wee while but close enough for the gasket to take up the slack so to speak.
    I had tried that approach before John and still had problems with the C&A gasket 'walking' between the head and the manifold and eventually failing. This is what happens with a Traction Avant engine. You may get away with that approach with a different car.
    Last edited by gerrypro; 12th October 2018 at 08:10 AM.
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    Cheers Gerry

  6. #6
    Real cars have hydraulics DoubleChevron's Avatar
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    91 is the go ... it'll probably run worst on the higher octane fuels as the compression ratio is very low. Put the cheapest crappiest low octane fuel in it you can find These things were designed for the fuel made back in the 1930s!
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  7. #7
    1000+ Posts gerrypro's Avatar
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    Quote Originally Posted by RossDel View Post
    I started on 91 with a cap of flashlube per fill but have switched to 95. Is 95 the way to go?
    50mm of flash lube to 1 Tank of 91 ( Approx. 50-55 Litres ) is a better ratio. Flash lube is sold in 50ml plastic bottles. I buy several of theses and keep them in the glove box. As they are used I refill from a 1 litre bottle.
    Cheers Gerry

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    Quote Originally Posted by DoubleChevron View Post
    91 is the go ... it'll probably run worst on the higher octane fuels as the compression ratio is very low. Put the cheapest crappiest low octane fuel in it you can find These things were designed for the fuel made back in the 1930s!
    Hi
    Yes the low compression ratio needs only the lowest octane rating fuel. However putting higher octane in, eg 95 or 98 will do no harm, and they supposedly have more beneficial additives to keep the system clean which may help in the long term. The "extra octanes" do not cause any problems if not needed. I use 98 in my old motorbikes and small engines as it seems to be less gummy and does not cause as many problems when sitting around.
    However do not use E10 or any alcohol blends as it will "eat" your old rubber and gaskets possibly and even the diecast parts.
    Jaahn
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  9. #9
    Real cars have hydraulics DoubleChevron's Avatar
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    Quote Originally Posted by jaahn View Post
    Hi
    Yes the low compression ratio needs only the lowest octane rating fuel. However putting higher octane in, eg 95 or 98 will do no harm, and they supposedly have more beneficial additives to keep the system clean which may help in the long term. The "extra octanes" do not cause any problems if not needed. I use 98 in my old motorbikes and small engines as it seems to be less gummy and does not cause as many problems when sitting around.
    However do not use E10 or any alcohol blends as it will "eat" your old rubber and gaskets possibly and even the diecast parts.
    Jaahn
    Yeah, I find the high octane stuff seems to "go off" really quickly unless used right away though ( probably in my head) -- so that is interesting. We have found the opposite with high octane fuels. After sitting in an vented tank for a month .......................... its probably back to 90 RON rather than 98 I always put 98 in my CX ( petrol turbo with a knock sensor ) if I can find it ............ but not if its going to sit. 91 seems to last better in the tank if the car isn't going to be driven

    seeya
    Shane L.
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    '78 GS1220 pallas
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  10. #10
    Tadpole
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    Thanks Gerry

  11. #11
    Tadpole
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    My vacuum advance to the Lucas distributor was not connected when the vehicle was purchased (terminated at carby). Neither is the manual advance/retard on the dash cable installed.

    I did replumb it after purchase but it wouldn't run at all after several minutes on road when initially connected. This was before I replaced the air filter / plugs / oil and tightened the manifold. The new vacuum pipe is still there ready to go at next step.

  12. #12
    1000+ Posts gerrypro's Avatar
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    Have you done a suction test on the vacuum advance capsule? It is possible for the diaphragm to be perforated. The Big 15 distributor is just like the one installed on later Morris minors but it is a mirror image version, However it is possible to fit a vacuum capsule from the Morrie. The graduated markings end up on the underside instead of being visible from the top. IIRC the link arm of the Morrie version needs to be reversed so that it is possible to connect it to the points carrier plate.
    Cheers Gerry

  13. #13
    Tadpole
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    Thanks Gerry, we have a Lucas expert at the Cootamundra Antique Car Club and I will ask him re that Morrie interchangeability (when he had a look at the engine for a second or two when he first saw the car he did suck on it and thought it was advancing ok at the distributor side. Next step for me is to actually find my vacuum gauge last seen in the 1980s.

    As you can likely tell it is me that needs tuning up as much as the car.
    gerrypro likes this.

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