I have to drill and tap out the two exhaust manifold bolts on the drivers side exhaust manifold. The question I have is about the tap. I have a cheap set of taps that seem to cut too much out (the bolts seem a fit loosely in the threads when finished) and the cutting edge of the tap appears dull. I am assuming I need to buy a fresh tap(s) but I am unsure who makes a quality set of taps nowdays? I haven't finished drilling out the broken bolts yet but hope to do so this coming week. Any suggestions would be much appreciated. Thanks, Robert
MSC Industrial is one place. https://www.mscdirect.com/ Or you can find a local industrial tooling supply company in your area. Your local machine shops would be able to tell you who they use when they need to buy a tool right away. The taps they sell at hardware stores are generally junk, in my experience.
My 2 cents worth, Winter and Greenfield both make a good tap. I have a couple questions for you, what size is the hole you drilled? is it correct for the tap? Does the hole you are tapping have a bottom or does it go through the the material? If the hole has a bottom, do you have all the taps you need to do the job, starter , plug and bottom? What are you using for lubrication when cutting the threads? Are you cutting the threads by turning the tap in a half turn and then backing it up and then moving forward a half turn? Good Luck with your project.
Thanks for the recommendation Jim. Yes, I would agree about the hardware stuff being junk. The time when you could purchase quality tools at the local stores seem to be gone. IlliniGSX, Thanks for the recommendation and questions. Right now I am in the process of sneaking up on the minor diameter of the broken bolt (at 7/64). The existing bolt is a 3/8. I am going to continue moving up a drill size at a time and then try to pick the threads out. Never had any luck doing that on exhaust manifolds but you have to try the easiest thing and gradually move up. If they don't come out at that point I will have to overdrill, probably to 1/2, tap and install studs. I don't believe that 7/16 will completely clean out the old threads. On this exhaust manifold the holes go all the way through the flange. If absolutely worse came to worse I could file a flat on the top of the flange and just use a bolt and lock nut but that would be the last option. For lubrication, I would use the same lightweight cutting oil I am using when drilling. Yes, I learned to run a tap in a little then back it out then repeat.
