Tech Theory: Threadlocker 101
In this story we’ll review the different types of threadlocker compounds and their applications. Threadlocker is used all over the world and is found on most new motorcycle hardware. I think most of you know that the early Harleys were prone to vibrate a bit, sometimes causing bolts to shake loose and fall off! The remedy is to put some threadlocker on the threads, inside the bearings or on any other piece that needs to be fixed for good.
When it comes to threadlocker, how many of us know what to use and how to use it properly? Normally, most of us clean parts with either a contact or brake cleaner. Well, that is a good starting point, but how many use the primer that goes with it? And do you even bother to check the expiration date on those products? Probably not.
Here are the basics on how to use the primer, when it is necessary to use it and when it’s unnecessary. The primer is there to activate and ensure the products will cure better and faster. Remember, the main goal is to hold two parts together and make sure nothing comes loose from all the vibration. Primers are used when the surfaces to be thread-locked and sealed don’t provide for proper curing to take place, or when the curing needs to be accelerated.
There are two types of metal surfaces: active, which doesn’t require primer, and inactive, which does. Active surfaces are brass, copper, bronze, and iron. Although active surfaces don’t require primer, it’s still recommended to use. Inactive surfaces are stainless steel, anodize, magnesium, and passivated surfaces, ie zinc, titanium, nickel, aluminum, and black oxide.
Threadlocker is generally classified into three different classes when talking about its use on motorcycles. The first group uses the blue compound for medium thread locking force. This is for those times when a good compromise is needed between locking parts together and still being able to take them apart without too much force.
The second group is the red compound, which is made to hold parts together without worrying about them becoming loose in the future. I suggest adding some heat if you want to take them apart.
The third group is the green compound, which is good for locking bearings, bushings, or seals in their housings. It also works well for smaller gaps.
The main goal is to make sure that the product works every time, so you don’t lose parts off your motorcycle! So be sure to use these products prior to the expiration date. After that date they will not work as well as designed. The longer they are past expiration, the greater the likelihood of failure. While the products will still be usable, be aware that you might end up with less bonding force than expected. If using threadlocker sparingly, it makes sense to buy it in smaller sizes and well before the marked expiration dates.
While on the subject of threadlocking products, there is another product to be considered when trying to bond two plastic parts together. Loctite sells a product called plastic adhesive promoter that serves as a primer to make sure all types of plastic material bond together, including those with high petroleum contents. These also have an expiration date.
I should add that when using any threadlocker product on a motorcycle, keep in mind that torque specs will vary, as much as 20 to 30 percent less, due to the lower amount of friction between both parts before they interact together. Basically, it’s like adding oil on the threads before torquing the bolt. Hardware that came from the factory with threadlocker on it will have the proper torque specs in the service manual. When adding threadlocker to older motorcycles that didn’t originally come with it, it’s important to reduce the torque setting, otherwise you risk damaging the parts.
This story is being shared from our sister media outlet, Classic American Iron Magazine. Check out CAIMag.com for more helpful vintage tech. AIG Back Issues