Between Saturday morning and this evening I was able to perform a repair to a motorcycle engine case for a fellow forum member.
The drain plug threads were stripped as well as an earlier attempt to repair and it looks like maybe some JB Weld was possibly used as there was what appeared to be some residue in the previous weld.
New drain plug.
Piece of 6061 I’ll use for the slug.
There’s a couple ways I could have gone about this. One would have been to machine the existing bung completely off and replace with a new bung. The other was to build up around the existing bung with new weld using 4043 rod and displace the porosity from the casting then bore out and machine a threaded slug to press into the bore and weld.
I chose the latter for the main reason being that the case was fairly thin at this point and much heat at all may have severely warped the area without the cast in bung to give it rigidity. By creeping up on the thickness by adding material I could control the heat much better and float the impurities from the casting to the surface, remove them and add more material in increments until I obtained the thickness I was after.
Material added and the impurities removed with lightly using a carbide burr.
When using carbide burrs on aluminum I like to repetitively dip the burr in Formax with a light coating to prevent the burr from plugging up.
Engine case set up on the mill table using an angle plate and Kant Twist clamps.
Machined flat.
Centering up on the bore of the drain plug.
Bored out to .750”.
Machining a slug.
Drilled and tapped to 10mm x 1.25 thread. The slug is about .001” larger than the bore for a slight interference fit.
I put the slug in the freezer for a couple of hours while I mowed the lawn. Then heated the case to a couple hundred degrees and used the drill chuck in the mill as a press.
Slug TIG welded into the case.
Completed.
I placed some 400-grit sandpaper on the surface plate and lapped the case half as a final check.
Boxed up and ready to go back to the owner.
Thanks for looking.
