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Thread: Diameter of DDHF 42 Solex throttle shaft?

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    Diameter of DDHF 42 Solex throttle shaft?

    I need to re-bush the throttle shafts on my Solex DDHF 42s ('72 1,600). Can anyone tell me the diameter of the throttle shafts so I can buy a reamer before I disassemble the carbs? Thanks.
    Thor Frohn-Nielsen
    '72 Lancia Fulvia 1600

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    Legendary Lancista Marnix's Avatar
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    Re: Diameter of DDHF 42 Solex throttle shaft?

    All solex carbs on the Fulvia have a 8mm spindle. Be aware that sometimes oversize (typically 8.2 or 8.5 mm) have been substituted, the bushes bored out to that oversize as a quick fix to worn out bushes.
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

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    Legendary Lancista Marnix's Avatar
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    Re: Diameter of DDHF 42 Solex throttle shaft?

    Another thing: don't fit STRAIGHT bushes. They need to have the curvature of the barrel on the inside, or you got a quite considerable air leak.

    Contact me for more details if necessary.
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

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    Re: Diameter of DDHF 42 Solex throttle shaft?

    Quote Originally Posted by Marnix View Post
    Another thing: don't fit STRAIGHT bushes. They need to have the curvature of the barrel on the inside, or you got a quite considerable air leak.

    Contact me for more details if necessary.
    thanks very much for both pieces of advice, Marnix!
    Thor Frohn-Nielsen
    '72 Lancia Fulvia 1600

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    Legendary Lancista Marnix's Avatar
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    Re: Diameter of DDHF 42 Solex throttle shaft?

    Maybe I should expand a bit on the problem of the C.42 DDHF bushes.

    For some reason, the bushes of the C.42, while in some kind of brass material, are prone to wearing out rather fast. No idea why this is, but most C.42 carbs I had in my hands have the trouble. The problem is mainly around the outer bushes, the inner bushes are not as much affected (because they are in the centre).

    Replacing/repairing those bushes is a bit of a challenge: the bushes for the C.42 go all the way trough to the barrels, so they need to have the 42mm diameter curvature of the barrels at the inside. I have seen them replaced with straight ended bushes, which will leave a considerable air leak (hard to explain in words).

    I am only guessing, but I think Solex made the bushes a perfect fit by first fitting bushes in the raw cast, and then turning out the barrels with the bushes in place, so that the bushes were turned out perfectly with the barrels. They didn't fit them afterwards as far as I can see it.

    There are several solutions being applied to repair/replace:

    1. push out the worn bushes, and put new straight ended in. Bad idea as I explained above.
    2. bore out the bushes to an oversize (typically 8.2 mm) and fit oversize spindles of the same oversize (they are available aftermarket). Correct alignment of the boring out is a challenge however. Works fine if done correctly.
    3. mill out the existing outer bushes halfway (10mm mill with a 8mm pilot, aligned first very well on the milling machine), and put a SHORT new straight bush in the milled out opening. Only, shouldn't mill too deep, as the most inner part of the existing bush does not have knurling completely up to the inner end. I have seen they have milled out too far, up to the inner part of the existing bush that is devoid of knurling, so that the remaining original end is not held firmly in the body anymore.
    4. put in straight bushes that exceed into the barrels, and turn out the barrels with the bushes in to oversize (e.g. 42,1 or 42,2 mm), and fit same size oversize butterflies. This is a copy of the original Solex operation. The inner ends of the bushes are now perfectly turned out with the barrels.
    5. Make new outer bushes, with the right curvature. It is easier than it sounds. I put the bushes on a special made holder, and put it on the lathe against a cylindrical grinding stone that I turned down to 42mm. To fit, I have a special made half round 42mm cylinder that I can put in the barrel so that when pushing the bush in, it gets perfectly aligned with the barrel by the half circle cylinder being pressed from a rod from the inside against the opening. This is by far the best solution of them all, just replaces the old bushes by new ones. I don't know of anybody else doing this (which doesn't mean it is not being done). I have done this several times, works OK.

    I still have to put the ultimate solution that I got into practice: mill out part of the bushes (e.g. halfway) at 10mm, mill out again at the outside to 12mm for 3,5 mm, and put in mini ball bearings at the ends (you need to have a bit of 10mm space behind the ball bearing, to be able to pull them out if later proved necessary to replace them). This is the perfect and final solution: the carbs will never wear out again, as the spindle and butterflies will now turn completely isolated from the body; the spindle and butterflies simply don't touch the body anywhere (well, a tiny bit at the inner bushes, but those won't wear out from it). Only thing that could wear out (presumably after a long time) is the ball bearings themselves, and those can be replaced if ever necessary. I did this solution for a C.35 PHH, works perfectly, just very careful alignment is required. I don't see any reason why it couldn't be done for the C.42, only the alignment on the C.42 is slightly more difficult. It is just that I didn't get that far on a C.42 yet due to lack of time, and I didn't want to mess up carburetors that I are not my own when working on a set for somebody else.
    Lancia Fulvia 2C 1964
    Lancia Fulvia Coupe Rallye 1,3 1968
    Porsche 924 1979
    Alfa Romeo 33 1.4IE 1993

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    Re: Diameter of DDHF 42 Solex throttle shaft?

    Quote Originally Posted by Professorgearhead View Post
    I need to re-bush the throttle shafts on my Solex DDHF 42s ('72 1,600). Can anyone tell me the diameter of the throttle shafts so I can buy a reamer before I disassemble the carbs? Thanks.
    [quote]
    you can buy the bushes from omicron that do not need reaming

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    Re: Diameter of DDHF 42 Solex throttle shaft?

    Thank you Marnix and Jensen1!
    Thor Frohn-Nielsen
    '72 Lancia Fulvia 1600

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