Thread Maintenance &
Repair On A Pro Saw
A pro saw is like a prize fighter -- even the most cared for lives a hard life. It goes to work each day, often in harsh conditions. While at work, it may get pinched, dropped, or whacked by a limb. Even in the hands of a careful user, it occasionally gets hit so hard something breaks. When it does, repair often includes removing broken screws and fixing stripped threads.
Vibration is another enemy of a saw engine's fasteners. Even with no impact damage, engine and cutting vibration shakes things apart. When screws loosen, stress transfers to the remaining fasteners. If not attended to, this may break housings and strip other screws.
Fortunately, with the right tools, thread repair is not difficult. Properly done, it can restore threads to “good-as-new” condition. Combined with regular fastener maintenance, thread repair keeps a pro saw in the woods where it can do its job.
There are a number of thread repair systems on the market. In our shop we have tried many, and the one we prefer is the Time-Sert. We like it because its inserts are a one-piece thin-walled steel bushing. This bushing has synchronized internal-external threads, and a locking feature that holds it in place. Installing a Time-Sert does take a little more labor than some of the other thread repair systems, but we think it is worth it. The few extra steps are easy to do, and the kit comes with all the necessary tools.
A Time-Sert kit is a moderate investment, but the inserts are not expensive. Once you have the tools, repairing stripped threads is very economical. If you consider the price of replacing the components you are able to repair, a kit quickly pays for itself.
Time-Sert kits are sold in specific thread sizes. Each kit contains a drill bit, a counter-bore, a cutting tap, and an insert driver. It also contains a number of inserts. Once you have a kit, the only other tool you need is a “T” handled tap driver. This fits the square shank on the top of all the Time-Sert tools. If you have other threading tools, it is a standard tap driving wrench. If you don't have one, it is also available at Madsen’s.
These are the four tools necessary for installing a Time-Sert. Along with some inserts, they are the components of a Time-Sert kit.
How to Install a Time-Sert
Step 1. To install a Time-Sert, begin by drilling out the remaining threads in a stripped hole. Often when a screw strips out, some of the old threads may remain. The drill-bit tool will remove the remaining threads, while sizing the hole for the tap. When drilling a chain saw case, an electric drill is not necessary because the case material is an aluminum alloy, which is fairly soft. Simply attach the “T” handled wrench to the drill-bit tool. What is left of the old threads can be easily removed by hand.
The drill tool removes any remaining threads. Since a chainsaw case is made of an aluminum/magnesium alloy, the threads are fairly soft and can be easily removed by hand.
This is a close-up photo of the stripped hole after the threads were removed with the drill hole.
Step 2. Attach the “T” handle to the counter-bore tool. With the counter-bore tool in the top of the hole, place some down pressure on the tool while rotating it. Small teeth on the side of the tool will cut a recess in the top of the hole. This recess is for the lip on the top of the insert. The recess needs to be deep enough so the lip of the insert can fit down into the hole, leaving the top of the insert flush with the original top surface. If the recess is not deep enough, the insert will protrude from the screw hole, making it impossible to mate correctly to another flat surface.
This tool cuts a small recess in the top of the hole. The top of the new insert will fit into the recess this tool makes.
In this photo, the tap is about to be positioned in the hole, but pay special attention to the recess that was cut by the tool above.
Step 3. Attach the “T” handle to the tap tool. Place it in the hole and cut new threads its full depth. If the hole is not open on the underside, be sure to run the tap past the point where the insert will stop. If the threads are not deep enough, the insert will not fit.
Here, new threads are being cut with the tap tool. This tap is special sized to accommodate the exterior threads on the insert.
This is a threaded hole that is ready for an insert to be installed.
Step 4. Attach the “T” handle to the driver tool. Select an insert of the proper depth and thread it on the driver tool. Put a couple drops of Loctite #271 on the outside of the insert. We like to use the red colored Loctite in our shop because of its strength.
Here, the insert tool is shown being used to thread the insert into the hole. Look closely and you can see the recess it will fit down into..
Once the insert seats into the recess, the installation tool expands and forms threads in the bottom of the insert, locking the insert into place.
Next, gently screw the Time-Sert into the hole. The shoulder on the Time-Sert should bottom in the recess you created with the counter bore tool. If the insert hangs up part way down, do not apply much force on the driver tool. If you do, it may begin to flare the bottom of the insert prematurely causing it to get stuck part way into the hole. Instead, remove the insert and find out what is stopping it. Sometimes it is helpful to run the tap through the hole again to insure good clean threads.
Now, try again. Gently thread the insert in until its lip bottoms out in the recess and its top is flush or slightly below the original surface height. Now, begin to turn the driver tool with some force. As you turn it, it will tighten the insert in the hole and then begin to flare the base portion of it. This flare is what locks the insert into place. Continue turning the insert tool until it turns freely.
At this point, the insert will be locked in place and bottom threads will have been formed. Now, remove the insert tool. Congratulations. You now have a new set of threads. Try a new screw in the repaired threads. It should screw in and out very easily.
This is a close-up of a new fastener in the newly repaired threads. This fastener easily thread in and out with only finger force.
Tips for Installing Time-Serts
Time-Serts don’t work well in “wallowed-out” holes. If the threads you are trying to repair were run with a loose fastener for a time, the hole may have become “egg” shaped. For a Time-Sert to work, it must have the support of all the material around it. If the drill tool won’t return a hole with stripped threads back to a round shape, it is time to consider a different repair.
If space allows, a larger diameter fastener may be a better solution. If space is tight, you may need to weld the hole closed first. Once the hole is welded, you can then restore the surface and drill a new mounting hole. One thing to consider before you weld is, it may be more cost effective to replace the part rather than fix it. Welding is expensive and so is the time it takes to fit, drill, and tap a new hole.
Another tip is to use the longest inserts you can. When threads are deep, put in a long insert. The longer the insert and fastener, the more holding power it has. In some applications, like on some saw air-boxes, the threads are very shallow. Short inserts are required there. We carry inserts in different lengths. If you are unsure about which ones to use, ask us. If you are fixing the threads on a pro saw, we have probably done the repair a hundred times and can easily direct you to the proper length insert.
How Good is a Time-Sert Repair?
Some users say that when used on a chain saw case, a properly installed Time-Sert provides better threads than the originals. Since most cases are made of aluminum/magnesium alloy, threads are fairly soft. These threads become worn when used to secure components that are frequently removed, like a starter or air filter. A Time-Sert is made of steel, producing arguably more durable threads.
Tips for Removing a Broken Fastener
Removing a broken fastener from a saw's case can be difficult. Most removal tools work by drilling a hole in the fastener’s shaft. Since chain saw fasteners are usually small, this requires an even smaller drill bit. This process is made more difficult by the fact that if the drill veers out of the fastener's shaft and into the softer case material, it is impossible to re drill it. So, removing a broken fastener can be a slow, tedious, and risky procedure -- best left to a saw technician.
Thread Locking Cement
Some pro saw users like to use Loctite or a similar thread locking cement on their fasteners. This can be effective at keeping screws tight, but does not eliminate regular fastener maintenance. Thread locking cement can also make it more difficult to disassemble a component when other maintenance or repair is necessary.
If you choose to use a thread locker, make sure you use the correct type. Loctite is available in several strengths. For example, the type of Loctite you would use on a bar stud is different from the type you would use on a small screw.
The proper use of Loctite helps keep a pro saw's fasteners in place.
The improper use of thread locking cement can itself lead to broken fasteners. If you need to remove fasteners that have been secured with a thread locker, apply heat to the fastener. This will usually relax the adhesive's grip. You don't want to be the guy that must remove a broken fastener that is locked in place.
Repairing The Threads In A Plastic Component
On today’s pro saws, some components, like fuel tanks and cylinder shrouds, are made of plastic or some type of polymer material. These parts are light and durable, but require special fasteners. Like anything that's got threads, sometimes they get stripped.
When mounting holes are deep and have plenty of thread holding material deeper in, a good solution is to use a longer fastener. If this isn't an option, it is sometimes possible to put a slightly larger fastener in the stripped hole. If a mounting hole is open on the underside, yet another option is to switch the fastener to one with conventional threads that can be secured with a nut on the underside.
Another fix that may work when those listed above won’t, is to use a shim. A piece of nylon, like the end of a zip-tie, added to a hole, will sometimes force part of a self-tapping fastener into good holding material. This is usually not a long term fix, but it will work in a pinch when other repairs or component replacement is not possible.
A shim is sometimes a good temporary solution for stripped threads in a plastic component.
To keep the threads on your pro saw in good shape, regularly check to be sure the fasteners are tight. There is no substitute for catching loose fasteners before they cause a problem.
Loose fasteners that are not attended to damage the threads in the holes they are in and force other mounting points to pick up the load. This strains other fasteners and can lead to broken parts.
Loose fasteners often allow components to rub against each other, accelerating wear on mounting surfaces. So, even if stripped threads are later repaired, surface damage can make a full repair impossible.
Even when a saw is well maintained, threads can become stripped. When this occurs, a timely repair is the best solution.
We hope you've learned a few things about thread repair and maintenance on a pro saw. If you have questions about these or anything on your pro saw, please let us know. We are here to help you... That’s why we’re the Pro’s Choice.