hey guys. what setup are you using to bottom tap for 12mm studs with the head on? i found tap and extension in mcmaster carr, however, is the o.d. of the extension going to fit into the hole?
was going to weld a 1/4 drive socket extension to the top of a tap, but wont work. the heat of welding will make it brittle and snap the tap.

 

I welded a 5/16" 12-point socket on the end of the M12x1.75 tap I got from McMaster. The 12 point socked just fit over the 4 corners of the tap. I had no problems with the welding making the tap brittle. This seemed to work very well, as I was able to use various length 1/4" extensions as needed for the back studs. --Eric

 

just trying to learn more about the older models here. Why do you need to tap for 12mm studs ? Are the bottom of your hole tappered to where they don't fit ?

 

Bottom tapping allows more stud in the block for better clamping force. No difference in your engine versus a 98.5 I don't believe.

 

when cummins tapped the holes in the block, they did not bottom tap, just used a starter tap, so the bottom several threads are not fully formed. bottom tapping gives you full size threads all the way to the bottom of the bore. allows for 2 more engaged threads, and prevents you from having you clearance the valve cover to clear the longer studs.

 

Oh I see. thanks. That's not the case with mine. Guess they started tapping the whole way. I had room to spare even with barely any studs sticking out of the head.

 

some say bottom tapping isnt worth it, but others do.

it is a pain, takes a long time, and working in tight spaces, but I think if your going to do it, do it right the first time

just my opinion

 

It does not take that long...pull the head...do every right...ONCE!