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MG MGB Technical - stripped screw holes in carb

Does anyone have a good fix for stripped screw holes in the carb and the choke assy? I have a 79 MGB with the Zenith carb and hot water choke assy. When it works it is just fine, but in taking it apart several times I have stripped the screw holes in the "pot metal" that the carb and choke are apparently made of. I have used oversided screws, but they are now loose too. I am now using lock tite on them to hole them in place.....what have the rest of you done. I am resisting the mechanical choke mod...

Thanks
Lyle Abel

Maybe a machine shop can install a type of helio coil.
Kimberly

could try jb weld or other liquid metal
ste
Ste Brown

Drill it out for a helicoil. They are available at most automotive parts stores. You won't have another problem with it.

BH Davis
BH Davis

People should be very careful with those screws They are some bizarre thread that even I can't identify, and I specialise in such. And they have a tapered countersunk head to boot. They rarely give problems until somebody tries to use any of several common but wrong screws, then you are screwed, as they say. And at least one of them will contact the float if it's too long, so pay attention!

FRM
FR Millmore

I am not familiar with the Zenith carburetors, but the SU are all 2BA or 3/16 Whitworth. I don't think that helicoil makes a kit for those sizes, but Recoil does. Recoil kits can be purchased from British Tools and Fasteners at: http://www.britishfasteners.com/Merchant2/merchant.mvc or from Uni-Thread at: http://www.uni-thread.com/ To find out what size screw is used, send a query to either Chris Betson at: http://www.octarine-services.co.uk/ or Burlen Fuel Systems at: http://www.burlen.co.uk/ Cheers - Dave
David DuBois

Lyle,
Where in California are you?......my answer is contingent on your location.
Jim
J A Kelly

I could not find any known thread that matches the ZS choke screws, not BA, W, any American standard, or any metric standard. Possibly one of the odd specialized things, "arcane instrument makers series" or something. I note that some late ZS do use metric at certain points, ones apparently UNF.
FRM
FR Millmore

Do you think the MG guys used to have competitions about who can find the weirdest nut bolt or screw?
It sure seems like it at times. with their posi drives and strange mix of metric and imperial. Apparently the speedo screw on, for example, is used nowhere else on planet earth.
Has anyone got a full list of all the types?
Peter

well, regarding the question, I agree, drilling out, lightly coating the existing thread/screw with a silicone, then a JB weld or similar epoxy plug to reestablish the original diameter and thread configuration. I agree, you'll not find a proper heli-coil for that bastard thread, but then, maybe you don't care, eh? Vic
vem myers

Thanks to all for your inputs....I will try Recoil in hopes that I can get a helix small enough for this. I was told by local auto parts stores that they don't carry them that small...Thanks again to all who responded to my problem.
Lyle Abel

No problem to get Helicoil down to 2-56 from such as MSC, and screws to suit. Or similar Metric sizes.

The stripping comes from the screws being loose, which wears the threads, ham handed over-tightening, which strips them, and the use of unsuitable screws for repair. No such thing as epoxy is going to survive this treatment, though it might work for a while, with care.

The multitude of threads comes from threads being developed for particular uses before standardization. When they were standardized, each trade had input. Whitworth did a lot of this work in Britain, so it is natural that many British threads are based on the Whitworth form. Other trades had their own, which when standardized survived. For instance, the optical guys had need of accurate threads for thin brass tubes, this became BSB - British Standard Brass, probably what is used on the speedo drive attachments. Bicycle makers used a thread that was largely of only two pitches at different diameters; this carried over to motorcycles as CEI - Cycle Engineers Institute.
European and American forms were standardized in a similar manner, so there are three basic systems. As the Empire folded and as a result of WWII letting the Americans in, There was a move to amalgamate British and American forms as the "Unified" thread system; the Americans predominated so much of Whitworth's niceties were lost as the US system was adopted. But the resulting UN threads are better than the old US systems as a result.
With the further shrinkage of British industrial influence, and the emergence of reborn Europe, metrics came to dominate everything, hence the switch to metric.
This is further complicated by another amalgamation of French and German standards - Germany won this one, in the form of the DIN. This then had to deal with the Japanese Metrics, again not quite the same. The result is that while both DIN and Japanese systems meet the same standard, they frequently use different standard pitches on the same diameter, with the Japanese tending to use the finer ones, equivalent to UNF, while European manufacturers use something more like UNC.

FRM
FR Millmore

This thread was discussed between 30/05/2007 and 01/06/2007

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