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Threads... 750 crankcase studs

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AshimotoK0:
Need to revisit this . My CB750K0 crankcases had a broken off stud. It was one of the short ones at the front and the threaded hole was slightly recessed from the sealing face of the 'cases. I tried every method mentioned on all of the forums including  welding  a nut onto the old thread and get it really hot to enable removal, due to the heat and purchase achieved on the new nut head. However, because it broke off low down, it was difficult to weld and I only had a  MIG not a TIG welder, so that method was not successful. What I then did was to get a set of scrap barrels and located them onto the crankcase using the 'knock pins' to accurately  locate the barrels onto the crankcase. Then I got a piece of SS tube which was a tightish fit in the barrel stud hole and got a long series drill which was a good fit on the ID of the tube and drilled a pilot hole  into the remains of the stud. This worked really well as the drill was fully guided and the hole was pretty concentric on the remaining stud. Then I was 'out of sorts' for 18 months so the job was abandoned. I read at the time that Honda used specially tapered machine taps for the holes. Does anyone know about this. My mate suggested that I drill my 'pilot' hole out to the stud thread  tapping size and then I may be able to pick out the old threads. Or should I just go for running a tap down the hole and Loctiting the stud in? Or is there a special tap available?

Cheers ... AshD

Seamus:
Initially go by your mate's recommendation. Then try to pick out the threads. I jhave done it a few times with various parts.
My brother actually made me a set of short tubes that would fit over various size studs with pilot drills to suit. Same principal as you used on the stud. Put them somewhere safe and will have to sort them out as I have some work coming up.

I will have a dig and see if there is an answer to the stud thread in Hondaman's book.

Trigger:
Ash, if it can not be drilled find a engineering firm or tool maker with a spark eroder. This machine will take it out clean and not damage the thread.

AshimotoK0:

--- Quote from: trigger6969 on October 14, 2014, 08:53:36 AM ---Ash, if it can not be drilled find a engineering firm or tool maker with a spark eroder. This machine will take it out clean and not damage the thread.

--- End quote ---

Think I looked at spark erosion Trig but it was very expensive and he wouldn't give me any guarantees. I hate leaving rare stuff with other people I don't know, as  I have heard of so many horror stories. I do have another SS sleeve bored out to the tapping drill size.

Cheers ... Ash

Trigger:

--- Quote from: AshimotoK0 on October 14, 2014, 08:56:58 AM ---
--- Quote from: trigger6969 on October 14, 2014, 08:53:36 AM ---Ash, if it can not be drilled find a engineering firm or tool maker with a spark eroder. This machine will take it out clean and not damage the thread.

--- End quote ---

Think I looked at spark erosion Trig but it was very expensive and he wouldn't give me any guarantees. I hate leaving rare stuff with other people I don't know, as  I have heard of so many horror stories. I do have another SS sleeve bored out to the tapping drill size.

Cheers ... Ash

--- End quote ---
Ash, i don't know any toolmaker that doesn't have a spark eroder. They need this machine for when they break a tap in the thread. You will have to find a small firm or an old boy that will charge you a Tenner.

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