To install the insert you will need some simple tools.  An easy out, a continuously threaded M8-1.25 bolt, an M8-1.25 nut, several spacers, and an appropriate wrench.

Once the insert is started into the threads, remove the easy out and replace it with the M8 bolt and install a nut on the top.  Now you can use the wrench to run it in snug.

If it fits good, remove the insert, clean everything up with Braklean, apply a coat of JB Weld to the external threads, and reinstall the insert permanently.  Go easy with the epoxy, you don’t want any slopping up the M8 internal threads.

Once the epoxy cures, that sucker ain’t ever comin out so make sure you got it right.  If your lookin for a little better performance you can blend the insert in with a die grinder, but I doubt it ill make much difference.  The gas flow through this port at WOT is pretty much confined to the upper regions of the port.  I’ve tried a number of mods to the floor of the port, and they don’t make any difference on the poor man’s flow bench.

DragBikeMike wrote on 10/14/22 at 17:07:57:

Could you explain this further?

That is some seriously clever problem solving. Yeah, having a lathe is something I really want, but IF I had one, I'm not sure I have the skill to get it to do something like that.
Probably some Kinda learning curve goes into THAT.
Good stuff, Mike.

I’ve been running the Big Bore 4-speed for about one month.  The engine has about 1900 miles on it.  I wanted to fill you in on how the fastener modifications are working out.

The ¼-20 head cover bolts are solid.  No leaks along the joint between the head cover and head.  The special acorn nut is also dry as a bone.  I knew this repair works good since I’ve run it on other engines.  This fix is a keeper.

The 8mm cylinder head stud just below the exhaust port is also solid.  I check the nut about once per week and the nut is always tight.  At most, I may have rotated this nut a total of 1/20 of a turn (18°) in all my retightening attempts combined.  With the old setup, I generally got about 1/8 turn (45°) every time I checked it until the shoulder on the stud started touching the head gasket, at which point the fastener was no longer clamping the head to the cylinder.  I think this mod is a must for anyone running a 97mm bore and the enlarged exhaust port.  The copper head gasket associated with the 97mm bore is unforgiving.  It doesn’t have an embossed bead to compensate for any reduction in fastener stress.  The enlarged exhaust port reduces some of the beam-strength between the 9mm studs, so a solid 8mm stud in the center is critical.

I am very pleased with these repairs/mods.  

Hello and first of all thanks for the great solution. My right rear bolt has failed and have a major leak from it. Going to try your fix. When you say that the head must be removed for sealing of the oil passage and clean up does that mean the cover at the top or the top section of the head where the fins start. If so this is probably the most involved and complex repair I have done on the bike. Do you recommend the clymer manual as a way to help me get it done? Thanks again.