Use thread lockers to keep those parts bolted together

Monday, December 1, 2008

Whenever you have a mechanical situation with a bolt or nut you want to stay put, these handy retaining compounds will do the job for you

by Keith Berglind

"A little drop will do you" is the best way to describe the work of a thread locker chemical.

The common thread locker that most mechanics work with is Loctite. Yes, this is a brand name, but for many of us it is an industry standard word (used like the word Kleenex), so when I ask for Loctite, I want a chemical thread locker. Just ask your parts supplier what brand they stock.

Almost identical to thread lockers are the retaining compounds used when a tighter fit is needed with non-threaded jobs, such as splines, keyways and press-fitted shafts and bearings.

The operating theory of both is the same. The liquid chemical remains fluid forever, in its clean bottle, surrounded by air. But when a drop or two is placed in a tight thread zone, with no air, the chemical hardens. Not only does the chemical fill the thread space to prevent the threads from wriggling loose, it also grips the metal surfaces to hold the nut from turning off.

The retaining fluids provide an identical service in non-thread situations.

A common farm problem is the loose bearing that keeps working itself free, maybe moving along the shaft or allowing misalignment of a belt or chain.

A few chemical drops coating the area where the bearing and shaft mate will fill the gap and stop bearing travel.

So, whenever I have a mechanical situation with a bolt or nut I want to stay put, or a shaft mating concern, I use Loctite or a similar chemical. Since these are not every day applications for most of us, it is most likely you will only own one general-use chemical. One fit does all for most farmers.

However, if you are a serious user, then you are welcome to shop in greater detail. In general, thread lockers are rated by the size of the gap to be filled, the strength of the grip or the size of the bolt. There are chemicals for pre-assembly and post-assembly. We tend to prefer the pre-assembly versions. Put a drop on the bolt and then install the nut. The post-assembly fluids penetrate and flow into threads after you have everything tightened up. Just put a drop on each protruding thread.

There are times when there is a use for the optional primer, which decreases the set-up time and increases the breakaway torque on most fastened surfaces. It also allows cold weather application. So, if you are fighting with a bolt on your snow plow which keeps working loose, use the primer and the thread locker. With primer, the normal set-up time of 20 minutes is reduced to 5 minutes. Full strength is 24 hours.

Okay, so you have the bolt and nut all chemically locked up. How do you get them apart next time around? There are two common solutions: more force and heat. Take this problem as an example.

You are using a half-inch wrench on a 5/16-inch bolt/nut installation. You pull harder and harder. There's no rust showing and everything looks normal, but it's too tight. Maybe it was over-torqued.But, maybe the last guy used a thread locker.

There comes a point where you stop pulling the wrench. It's time to think.

If it was one of the weaker thread lockers, more wrench torque should break it free. That's OK if it's just a nut on a bolt, which can be replaced, but you do not want to break off a bolt in an engine block.

So, it may be prudent to try some localized heat. This is because thread lockers are designed to release their grip at higher than operating temperatures. The normal operating range is -65 to 300 F (-54 to 149 C), and when you heat it above that range, it loses its grip.

So, apply a lot of heat quickly to the threaded area and it will come loose. When in doubt, look carefully around the thread ends. When you see some red or blue material in the threads, assume it is a thread locker. BF

Keith Berglind is a licensed heavy-duty mechanic.