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Help : Broken threaded screw on Keihin carb

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If you can stay clear of the gasket, or make a hole thru it but still keep it intact, you could try drilling and tapping at the corners. Something around 2.0mm thread would be enough. The top will need a slightly larger hole for screw clearance. 

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If you can stay clear of the gasket, or make a hole thru it but still keep it intact, you could try drilling and tapping at the corners. Something around 2.0mm thread would be enough. The top will need a slightly larger hole for screw clearance. 
IMG_0244.JPG.af42c9fdf4dac45e6c80afd1096f7511.thumb.JPG.a177e40f195aa6139acc3304c63e0f5e.JPG


Brilliant! Thanks for that!

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Boy!! I think takes some careful work to drill and tap a 2mm (.079") hole.  That is about the size of the screws used in glasses to hold the lenses in.

I wold take a different approach.  File the remainder of the broken boss off the carb body.  Make a nut that is an "L" shaped "tooth" that hooks under the lip. Make it so you can tighten the screw so the tooth contacts the cover and is hooked under the lip. That would be pretty secure.  Keep in mind the cover is a dust cover not a vacuum leak if it does not seal well.

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If you're not comfortable doing that repair take it to a machinist. There's not any room for error there. You'll only get one shot at it so take your time and do it with precision.

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Posted (edited)

If it's just a dust cover, I would drill the two round bosses in the first pic and safety wire it.

Edited by Rhinoracer

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Here's my first thought that a lot of people won't like.  If you have the screw, put it back in the hole and coat it with wax or oil on the threads. Make sure that the body of the carb is clean (brake cleaner), and fill that area with JB Weld or similar.  Let it dry, remove screw and drill/tap or add a washer to the screw and use. 

Obviously, having someone weld metal in and then drill and tap would be best, but this metal is hard to work with.

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Posted (edited)
1 hour ago, Noble said:

Boy!! I think takes some careful work to drill and tap a 2mm (.079") hole.  That is about the size of the screws used in glasses to hold the lenses in.

I wold take a different approach.  File the remainder of the broken boss off the carb body.  Make a nut that is an "L" shaped "tooth" that hooks under the lip. Make it so you can tighten the screw so the tooth contacts the cover and is hooked under the lip. That would be pretty secure.  Keep in mind the cover is a dust cover not a vacuum leak if it does not seal well.

Lol. I'm retired from doing R&D for a medical device Co.  I sometimes lose perspective on big vs. small. I think 2.0 mm will still work, but if possible 2.5mm or 3.0mm would definitely be better. Tap with a pin vise (not a T handle) if possible.

IMG_20190418_151046.jpg.367a6c645bfff97d35e6645f8afa7fd5.jpg

 

Edited by 76xtdrvr

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That carb looks well used, so I would just clamp it on until I know it's not in need of tons of money thrown at it.

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Here is a thought..Its not the correct carb to swap onto a DRZ.... So don't repair it at all>
Its a well used carb, if you insist on repairing it and trying to fit it to a DRZ, have it cleaned and inspected by someone capable of spotting the wear it most  likely has which will make it a never ending game of "why wont my "new" carb run well"  If after inspecting its deemed not too worn out.. This is one of the few times Id ever suggest using epoxy metal products. You can clean the area up, form a nice blob and fill that area solid, then drill and tap for threads. You can take a bur and gouge out the broken threads, use a small thread insert and form the epoxy metal arounds it and carb.

 
 

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So.....    That could be easily fixed with a suitable nut and JB Weld.    What I would do is use a Dremel tool to cut a nice, neat slot in the broken screw tab, or boss, or whatever you want to call it.   Cut the slot more or less parallel to the broken threads (horizontal using your picture), and be very careful to make the the slot just barely large enough for the nut to fit in.  Make sure the slot is deep enough that the threaded hole in the nut aligns well with the screw.  Once all that fits together to your satisfaction, neatly JB Weld the nut into the slot.    (If you are not positive about the alignment just use a tiny amount of JB Weld to stake it in place, such that you can remove it and re-align if necessary)  Make sure everything is clean before bonding, and be sure to not get any JB Weld in the threads of the nut.    Once the JB Weld is cured, and alignment is confirmed, you can add some JB Weld for extra strength.   

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Clearly there are several different ways to fix it depending on tools and experience available.

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So I ended up doing something like Rodzilla55 suggested. With the dremel, cut off the broken tab and put the aluminum flush to the rest.

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Then JB Weld a nut to its proper place, let it dry.

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Made sure everthing aligned properly and then added more JB weld. A good snug on the allen bolt and everything is properly sealed tight.

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Thanks everyone for all the suggestions!


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Great work ,  everybody ....    good advice ,  different views  ,   job well done ...

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