Loctite, which one?

[NPS]

I would be grateful for some views on what strength of loctite is needed for engine reassembly. There are low strength and high strength options.

For instance the flywheel bolts, oil pump and clutch housing all use loctite. Is it the same strength in each case?

 

[scottmastrocinque]

There are four types actually - in order of strength - Green, Purple, Blue and Red.

I avoid Red for most everything except things like engine cylinder studs - things I know are going to be permanent unless there is some sort of catastrophic failure requiring an unexpected tear-down or major overhaul. If it is a part that I expect to replace or renew in the future, then I never use Red - I use Blue, and it has never failed me ever. I have never experienced the loosening of a bolt I tightened with Blue Locktite.

Unfortunately, I have had a fair share of bolts that people assembled with liberal amounts of Red on them, and it has been an exercise in frustration and damage control, to remove those bolts safely when Blue would have been just fine.

My rule of thumb with regard to Red is: Assume this is going to be a permanent bolt that if you ever want to disassemble, it will require both large amounts of heat and effort! Also, the adage "Less is More" applies to application of Red Loctite. This stuff is STRONG and you can fuse a bolt into place with it where the bolt literally shears off when trying to remove it!

In honesty, I've seen Red called for on brake caliper bolts, and oil pumps, but if you look at the Technical Specifications Sheets, both Red and Blue have the same retained % of original holding capacity in the presence of oil and I've yet to encounter a brake caliper bolt at 650ºF. Unfortunately, removing calipers in order to facilitate wheel removal and tire changing, occurs fairly often (~ 6k miles) so I'd hardly call those bolts "permanent" and I for one don't want them behaving that way when I have to remove them. I personally have never used Red for any of these applications, I used Blue and have had no problems. You have to use your own judgement though.

For 99% of my applications requiring a thread-locker, I have always used Blue Loctite very successfully. In fact, my V10-Centauro manual from the Moto Guzzi factory calls for Blue on the flywheel bolts to the engine! Those are stressed bolts for sure!

Purple is like Blue but for lower temperature applications and fine machine threads.

Green is for delicate applications.

Hope this helps. Good Luck!




Green Threadlocker - Low Strength, Wicking Grade Threadlocker for Pre-assembled Fasteners

Green color, removable with heat and hand tools, for preassembled fasteners, instrumentation screws, electrical connectors, carburetors and fasteners.

Features:

• Used for wicking applications.
• The optimum temperature range is -65ºF to 300ºF
• Easy removal
• Ideal for small screws
• Pre-assemble

Purple Threadlocker - Low Strength, Easily Removable Threadlocker for Small Threads

Purple Threadlocker prevents loosening from shock or vibration, but also allows for simple, hand-tool disassembly without shearing the screw.

Features:

• Low strength
• Easy to remove liquid threadlocker
• Typically used with small screws up to 1/4".
• The optimum temperature range is -65º F to 300º F.

Blue Threadlocker - Medium Strength, Removable Threadlocker

Fill spaces between threads to produce a secure one-piece assembly that will not loosen under stress, but can be removed with hand tools.

Features:

• Removable with standard hand tools on ¼ to ¾ fasteners.
• Available in liquid, stick, paste, gel and tape form.
• Fast fixture times.
• Optimum temperature range is range -65ºF to 650ºF.

Red Threadlocker - High Strength, High Temperature Threadlocker

Permanently lock and seal threaded fasteners up to one-inch in diameter. Red LOCTITE Threadlockers are designed for high strength and high temperature applications.

Features:

• Designed to deliver high strength on ¼ " to ¾ " (6 mm to 22 mm) fasteners
• Optimum temperature range is -65ºF to 550ºF
• Disassembling requires localized heat (>550°F/260°C), hand tools, and disassembly while hot

 

[abbienormal]

Every time I run across someplace where someone used Red when it should have been Blue that person is normally referred to as anything but a child of God and much cursing and heat follows. Like Scott I use blue quite a bit and it really doesn't take a lot.

 

[john zibell]

Check the factory manual. If it calls for thread locker use anything but red (except maybe for cylinder studs). Every engine I've disassembled has not had any thread locking compound applied at the factory, but I haven't disassembled a Breva engine yet. I've only found thread locking compound on brake rotor bolts. Currently I have to replace the pan screws for a MkV Lemans. I've only been able to find stainless steel screws of the correct size that won't rust. Those will be installed with an anti-seize compound. If you use loctite on threads that will act as a lubricant on install and change fastener stretch at the torque value applied. If no thread locking compound is used, applying the correct torque will prevent fasteners from coming loose.

 

[NPS]

Would you believe me that I have just found red used in the CARC bolts holding the case together. They were quite easy to remove as the stuff was in a narrow band. Perhaps this is a different brand of red with lower strength.