Thanks all for the input on this. My original thinking was keeping the original setup so the muffler ends up in the same place and I can keep all the original heat shielding and brackets. The muffler has bolts in the back of it for mounting to an existing bracket. I would need to keep the same spacing on everything for it all to fit, which means the engagement of the muffler on the exhaust fitting would need to be the same distance off the block. The 3/4" NPT tap was only 15 bucks but thank you 5030 for the offer, I appreciate it. The right port appears to be cross threaded and some chunks busted out of the threads, lining up the tap properly is going to be tricky if even possible. The left port looks usable as is. Or, I ditch all that and just throw on some generic muffler. The threaded holes on either side of the ports are in great shape so either way it looks like I have options. My boys are having fun working on it so it's all a win for them.
mrmikey
Veteran Member
Watch when you run the tap in you don't go too deep. Yours could be different I can't tell but on the smaller BS engine the intake valve stem is right there, go too deep and you're into the valve. Ask me how I know 
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The depth will entirely depend on if the tap is a bottoming tap or not, but in any case with NPT threads, you don't need to run the tap in far as the tapered design of the tap only needs 3-4 full threads. Bottoming taps will have thread profiles to almost the end of the tap whereas other taps (through taps) won't have thread profiles to the very end and pipe taps are only supposed to cut 3-4 full threads anyway. If I was doing it, I'd remove the head and do it on the bench with the head secured in a vise anyway.
mrmikey
Veteran Member
Didn't think there was such a thing as a bottoming pipe tap it being a tapered thread?
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There is sort of... If you run the tap in too deep all you do is defeat the purpose of the tapered tap.
ultrarunner
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Early on rehabbing old houses one of the first expensive purchase was a set of pipe taps to 1.5” size starting at 1/8 th
Can’t tell you how many times being able to clean up buggered pipe treads proved to be a real time saver… and more than a few times this included small engine muffler work.
A tap loaded with grease will capture a lot of the threading chips…
Can’t tell you how many times being able to clean up buggered pipe treads proved to be a real time saver… and more than a few times this included small engine muffler work.
A tap loaded with grease will capture a lot of the threading chips…
etpm
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Yeah, bottoming pipe taps are common in machine shops. Oftentimes there is not enough material to use a regular pipe tap so either a bottoming tap is used or a regular tap is used and then a bottoming tap is used to get full threads. With CNC machines so common now pipe threads are milled instead of a tap being used, especially when larger pipe threads are needed. The torque requIred for larger diameter pipe threads is quite high so thread milling is the preferred method now. In my shop any pipe thread larger than 1/4 was usually milled. Faster to mill than tap too.
Eric
