Loctite 638 vs. 648: What’s The Difference?
Loctite 648 demonstrates faster cure, higher strengths, and better resistance to heat, chemicals, and aging compared to Loctite 638 based on the technical data provided.
Loctite 638 vs. 648: Specs & Uses
⏰Cure Speed in Larger Bond Gaps (0.25mm)
Loctite 638: Slightly faster strength development
Loctite 648: Slightly slower strength development
🆚Heat Aging Resistance at 180°C
Loctite 638: Retains 125-150% strength up to 5000h
Loctite 648: Retains 75-125% strength up to 5000h
🛠️Common Uses
Loctite 638 can be used to effectively eliminate those bothersome noises. It has been successfully tested on a direct fit MTB chainring, specifically Shimano XT cranks with an absolute black chainring.
Loctite 648 can effectively seal gaps, joints, or connections in metal components, providing resistance against leaks, vibrations, or environmental factors.
Technical Info
What Is Loctite 648
✅Loctite 648 Works Well As a Thread Locker
After many rides and washes, I’m happy to report that the creaks are still gone. It has truly proven its effectiveness in addressing this issue.
Works Well As a Thread Locker
In addition to its creak-eliminating capabilities, I have also found that this Loctite 648 retaining compound works well as a thread locker
(See more here: loctite vs permatex threadlocker). In fact, I’ve used it for that purpose with satisfactory results. In terms of thread-locking strength, I would place it somewhere between the Loctite 242 medium strength and the 271 maximum strength variants.
Creak Eliminator
Its functionality as a creak eliminator and thread locker has been impressive. However, it’s worth noting that there should be a certain amount of air in the container to prevent premature curing. Loctite products cure in the absence of oxygen, so the partial filling of the bottle is intentional and not a sign of being short-changed.
648 doesn’t need primers or activators to cure – it does it on its own. There’s no hassle with the curing process, and despite the “use by” date on the bottle, I’ve found that it still works years later.
Loctite 648 has a temperature rating of 180°C (356°F) and is ideal for heavy-duty applications like securing suspension bolts, retaining flywheels on lawn tractors, etc. For press-fit applications, it fills gaps up to 0.010″.
I love 648’s strength. After it cures, it takes 500°F (260°C) or higher to break down the bond, making disassembly tricky without heat or special solvents. It’s perfect for critical components that have to withstand high torque and radial forces.
❌Difficult to Open
Initially, Loctite 648 can be a little tricky to open due to its dispenser. You have to pierce through the top to get to the product, but once you do, it’s smooth sailing.
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What Is Loctite 638
✅Pros
Now, let’s get back to the performance. Loctite did exactly what it promised. It secured the bearings in my gearbox, ensuring smooth operation and minimizing any potential wobbling or shifting. I’ve had my fair share of disappointments with other products, but Loctite lived up to its reputation. It’s a reliable choice for mechanical applications, and I couldn’t be happier with the results.
I also used Loctite to keep a pinion gear on the motor shaft of my 31 lbs RC car, and it has been holding up remarkably well. It’s been through some intense off-road adventures, and the bond remains strong. So, if you’re looking for a solution to keep your gears in place, Loctite might just be the answer.
Speaking of the bottle, I lucked out because instead of the 50ml bottle I ordered, I received a generous 250ml bottle. Talk about a pleasant surprise! Initially, I was a bit skeptical since it was labeled as being from India. However, I soon realized that it was not a counterfeit product. But once I peeled away the tape, I discovered that the product was well within its shelf life. It was about 18 months old and still good for another 18. Phew!
❌Cons
Now, let’s talk about the bottle itself. When my package arrived, I was a bit alarmed to see that the bottle was only half full. Naturally, I wondered if I had received an incomplete product. However, after doing some research, I discovered that this is actually intentional. Due to the chemical nature of Loctite, the bottle is filled with air to maintain its effectiveness. So, no need to panic if you find your bottle half empty upon arrival!
FAQ of Loctite 638
Q: How much should a new bottle weigh? Mine feels kind of empty.
A: Ideally, the bottle should have a weight that indicates it is half empty. This allows for the necessary presence of air to prevent the content from hardening within the bottle.
Q: Can you provide the expiration date for this bottle of Loctite 638?
A: The expiration date is indicated by a code on the bottle. To decipher the code and determine the exact expiration date, it is best to contact Loctite directly.
Q: Why does Loctite arrive empty?
A: As I said, it is empty intentionally. If you put a drip of Loctite on the table, it is never gonna dry. That said, it is going to stay in that form because Loctite takes an absence of air to create the chemical reaction to harden it. That’s also why when you buy a new bottle of Loctite it feels like it’s kind of empty. It’s actually because they put it too much. There won’t be enough air for it to stay in its liquid form. The absence of air within the bottle will cause the entire bottle to harden.
I’m Ronald Stevens, a Mechanical Engineer obsessed with adhesives, glue, and all things sticky! My passion began in childhood when I’d always be the one playing with glue during arts and crafts. And I’d spend hours researching and experimenting. Happy reading, and remember: stick with the best, and you’ll never be stuck in a mess!
Feel free to contact me and join our discussion:
Can Loctite 638 be used on an O.D. rubber seal surface to metal housing, or is it only suitable for metal-to-metal applications?
It is specifically designed for metal-to-metal applications and may not be suitable for use on an O.D. rubber seal surface to metal housing.