How To

How To Repair A Thread - Dirt Rider Magazine

February 8, 2011

_Thread Repair

We have all been there if you have worked on dirt bikes long enough-you're tightening a bolt and that sick feeling rushes in when you suddenly feel that pop, snap or little or no resistance. If you're lucky, the bolt broke and you can get it out-simply install another. If luck abandoned you, the threads will need to be fixed. The problem is our bikes have a lot of steel bolts that thread into aluminum, brass or even plastic. That is not a good recipe for exceptional thread life. Depending on the damage, sometimes the threads can be cleaned up, but the tools we're looking at here are for more extreme cases. Unless the casting or other part you're working with is exceptionally thin with little metal surrounding the threaded hole, the threads can usually be repaired or, perhaps more accurately, replaced. There are several options on the market, but the leading two are HeliCoil (and the multiple knockoffs of that brand) and the Time-Sert. In both cases the stripped hole is drilled out and tapped to a larger, specific size and a coiled spring (HeliCoil) or a machined insert (Time-Sert) is threaded in. Making things easier these days is the fact that Flanders Company (www.flandersco.com) is a distributor for both brands, so you can order from the site or any dealer or repair shop. We repaired junk holes with both types of insert, and either work well for different situations. The Time-Sert install kit comes with twice as many tools as a HeliCoil kit, so it is more expensive but is also considered a better repair if there is room for the shouldered insert. Once you have the install kits you can simply buy more inserts. You will need an install kit for each size thread, though. Here is how it works.

1) Start by drilling out the damaged threads. If possible, use a drill press to make sure you get a straight hole. Otherwise, do everything you can to ensure the hole drills straight. If the hole is blind, make sure not to drill in too far. You just want to clean up the hole. Time-Sert includes the drill bit, but HeliCoil simply gives the correct size.

2) The Time-Sert kit includes this reaming tool that opens a step next to the hole. Insert the nose of the tool in the hole, then drill the reamer in until it stops cutting.

3) The reamer is designed to make an indentation that will leave the lip of the insert below the surface of the part. The integrity of the mating surface remains intact. This step is not necessary for the HeliCoil.

4) Both kits include the correct tap. In fact, for a given thread size both kits use the same tap. Make sure to use a generous coating of oil on the tap. The oil helps to wash the chips generated by threading into the fluted areas of the tap. Make sure the tap goes in straight. Turn it in carefully, but back the tap up out every so often to clean the threads.

5) With the Time-Sert, thread the insert in by hand a few turns. It can go in dry. You can use a thread-locking compound if you want, but Time-Sert claims it isn't needed. The installation tool that is included with the kit should be oiled, though. The installation tool threads in but hits resistance at the end of the insert. Then the insert threads in until the lip of the insert seats. As the tool continues through the insert, it spreads the lower end out. When the insert is fully installed any resistance to the tool goes away, and it turns in easily.

6) This is the HeliCoil kit. It includes the tap and the installation tool. You prep and tap the hole the same way before installing the insert. The initial buy-in is less than the Time-Sert kit.

7) Once the hole is tapped to size, put the insert on the installation tool like this. The wire tang should catch on the lip machined into the end of the tool.

8) Both companies claim that an insert 1.5 times the width of the hole is long enough. For situations where you want the existing hole fully threaded, both HeliCoil and Time-Sert have longer inserts available. The small spring-like insert is threaded into the hole. It should thread in until the top of the insert is 3/4 turn below the surface of the hole. It should thread in easily once you get it started. You must break off the wire tang at the bottom of the insert once fully installed. You can use a punch or a tool that's the same size as the hole inside the threads. Just smack it sharply and it will snap off. You need to get the tang out of the hole with a pick, small pliers or a magnet.

9) The finished repair looks clean, and it should be stronger than the original threads. You now have steel threads, and the threads holding the insert in are larger and therefore stronger than before.

Note: It's a differing matter of opinion as to which thread repair method is better, HeliCoil or Time-Sert. We feel that the area of the thread damaged will often determine which method you should use. For example, a HeliCoil may work better in tighter areas where there's very little room on either side of the thread for a gasket. If surface area is abundant, a Time-Sert may be the smartest option. For most low- to medium-tension jobs, a HeliCoil should do the trick, but you may want to pony up the extra dough for a Time-Sert if you're repairing a bigger thread for a head bolt, spark plug or cylinder stud. Regardless, it's generally agreed upon that both a HeliCoil and a Time-Sert will be stronger than the original threads. In fact, we've heard of engine builders installing one or the other as a precaution in high-use threads!