THE SHOP

Performance & Hotrod Business - July '15

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PRECISION ENGINE 2 n PRECISION ENGINE n July 2015 Restoring Male Threads If a bolt or stud features damaged threads, the correct fix is to simply replace the bolt or stud. However, in some cases you are faced with a male-threaded com- ponent that you prefer to save rather than replace. Common examples include spindle threads that have been damaged or deformed as a result of spindle removal from hubs and wheel hub studs. A variety of chaser tools are available for these appli- cations, ranging from one-piece chaser dies, split dies and adjustable dies that fea- ture a selection of thread chasing teeth and that adjust for thread diameter. Depending on the design of the chaser tool, restoring male threads will often require starting at the base and walking outward to the tip. In order to aid in male thread cleanup, before using the chaser die, closely inspect the tip of the shank. If the tip is burred or very sharp, it may be wise to first slightly radius the tip (with the use of a file or mini belt sander). Creating a slightly chamfered tip can make the eventual installation of the nut easier, helping to avoid initial cross-threading during assembly. Prior to using a chaser tap or die, first clean the existing threads by removing any dirt, rust scale, grease or other contami- nants to the best of your ability, using a solvent, bristle brush and compressed air. Quite often, these specialty reforming tools can save an existing thread, avoiding potential component replacement. Thread Inserts If female threads are stripped out, with insufficient thread material for the reforming process, the alternative is obvi- ous: either replace the component (cylin- der head, for example) or install a quality threaded insert. Thread inserts are available in several designs, including helically wound stain- less steel and solid inserts that are either locked into position by staking or with the use of an anaerobic locking compound. Regardless of the style of insert, the exist- ing damaged hole must be drilled to a spe- cific diameter and tapped by creating new threads that will accept the insert. Be aware that most inserts require a spe- cialized tap size that will match the outer threads of the insert. Unless you're already stocked with a specific thread insert brand's installation tools, it's best to purchase an insert kit that will include not only the required inserts, but all installation tools (and instructions) as well. Cutting Taps & Dies Taps and dies allow you to create threads. Taps are male cutting tools that create threads in a female hole. Dies are female cutting tools that create threads on a male rod or shank. Note: As we already mentioned, the vast majority of taps are designed for cre- ating female threaded locations. By their A Few Don'ts oF threAD Cutting AnD repAiring • If a bolt or stud's threads are stripped, galled or otherwise mangled, replace the bolt or stud. If the bolt or stud doesn't feature enough material to provide full-depth threads, you'll waste your time. • Never be in a hurry when running a tap or a die. Cutting threads is a precise process. Rushing the job will only cause problems. • Never guess or eyeball the size of the drill required to create a threaded hole. Take the time to look at a reference chart to determine the correct size drill for a given hole. • If you're dealing with a shallow blind hole, you must use a bottoming tap in order to create threads as close to the bottom as possible. However, start the threads with a chamfered tap, following up with a bottoming tap. A chamfered tap will provide an easier (and more accurate) initial engagement to the hole. • Handle and store your taps and dies carefully. Always clean them when you're done, and store them away from moisture. Before using a tap or die, check and clean the threads. • Remember that traditional taps and dies are designed for cutting and creating threads. Whenever possible, use a following, or forming tap or die to clean or repair existing threads, in an effort to remove as little metal as possible from existing threads. Assuring clean and smooth-spiraling threads in an engine block's head decks eliminates frictional variables during cylinder head bolt tightening, aiding greatly in achieving evenly- distributed bolt torque. An inexpensive set of chasers from Summit Racing. The set includes 1/4-20, 5/16-18, 3/8-16, 7/16-14, 1/2-13 and 9/16-12 sizes. Similar sets are also available in fine thread and in metric formats. From left: tapered chamfer tap, plug chamfer tap and bottoming tap. Spark plug hole chasers can save the day when dealing with a slightly damaged spark plug female thread in a cylinder head. This double-ended chaser from Lisle (P/N 20200) features both a 14mm and an 18mm spark plug thread chaser. A standard 13/16-inch deepwell spark plug socket wrench is required for driving this chaser. Note the three flutes on each end, which aid in evacuating any debris. This also eases the force required to follow the threads. A center O-ring secures the tool inside the socket wrench.

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