Page last updated July 17, 2008



Bolt Hole Rethreading / Tapping

First set of instructions will cover tapping new threads with and without helicoil.

With the powerhead flat, use a wire brush to clean out the hole or area needing repair. Make sure you get all rust, oil out. Punch an indentaion into the broken bolt body with a steel punch, try to get absolutely in the center of the area you are tapping out and take into consideration the threads as they are deceiving in determining the center of the bolt.

Now, with the powerhead on your drillpress worktable, position the press and try to plunge into an existing bolt hole to get the correct angle and depth. Assuming all bolts are the same size, you can either set the press stop or place a piece of tape onto bit indicating how far down you need to drill.

Common tools needed

You may have to develop some sort of jig in order to slide the powerhead to the area you need to drill. I have wood bolted onto my drillpress platform and I placed another piece of thick particleboard directly on top of the platform. This allows me to slide the powerhead where ever it needs to go. You can use clamps to keep it in place when ready.



What you want to initially try to do is remove only the bolt and not the powerhead metal. Start off with a bit that is smaller than the frozen bolt, essentially making a hole into the bolt. When angle and depth have been set, place some cutting oil on bolt head and slowly plunge the press into bolt and watch ensuring bit does no walk. Make sure you don't have a lot of the bit exposed as it will bend so shove it up as far as it will go into chuck. Work slowly, stopping every so often, inspecting your progress. You have to get it right the first time. The speed of the press is dependant on what the manufacturer of the bits recommends. I find 1900 RPMs to work for me but some require very high RPMs to cut properly. I normally use a magnetized tool to collect metal shavings of bolt followed by compressed air. You can also use compressed air for it all but it gets messy and make sure you wear safety glasses.


Then with a dremmel or rotozip, carve the rest of the remaining bolt out. It is a slow process but is the best option.

When you have finished and are satisfied with the work, you can go forward with cleaning the old threads free of the frozen bolt by using a sharp object and slowly proceeding to pulling / prying old bolt off of threads. When complete, you can clean with a tap.


For the bolt to the left, I went ahead a cored out the remaining portions of the bolt, threaded a Helicoil into good metal, then coated the top areas with brazing metal in order to create a seal for gasket area.


The results of my work to the left. The bolt is smaller than the original due to imperfections in the hole. It was difficult to create a tap the proper size due to the existing hole to the left of the bolt (picture on top). In hind site, I should have carved out more metal utilizing a rotozip and dremmel to accomodate the tap but I was fearful due to my disastrous attempt with a hand drill and wanted to keep as much of the original metal in place. (for an example of grinding additional metal so that tap will fit, see JB Weld area at bottom of page)

Each bolt and their size has their purposes and keep in mind that a particular size is used to prevent shearing of the bolt head and is capable of receiving so much torque. Though the bolt is smaller, the original bolt was a rated at 5, I went ahead and switched it an 8 which is stronger. The amount of torque I plan on applying to the bolt is not much and actually, there are 2 other bolts on the exhaust cover that have the same size bolt I used. It should do just fine as far as creating the required pressure on the gasket area.


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