Thread Locker - Appropriate Uses

[dennisv]

Where is it appropriate to use thread locker (aka Loctite) during engine assembly?

My primary resources for engine building have been:

• Porsche factory workshop manuals for 914-6 and 911
• Porsche 911 Performance Handbook by Bruce Anderson
• How to Rebuild and Modify Porsche 911 Engines by Wayne Dempsey
• Klassic ATS by Kurt Donohoe

Unfortunately, they don't seem to agree on this topic. Key examples are the case studs, head studs, and connecting rod bolts. Some resources suggest lubricating the bolts and studs to help insure accurate torque. Others suggest high-strength thread locker (e.g., red Loctite requires heat to remove) to prevent unwanted loosening. I guess the thread locker would offer some lubrication initially.

• Factory manual simply indicates: Lubricated for Connecting rod bolt threads and bearing surface of nut
• Bruce Anderson suggests: assembly lube should also be used on the rod bolts and any other bolts or studs where the torque is critical.
• Wayne’s book suggests: Loctite 271 (red) or Permatex Thread-Locker is required for rod bolts and head studs.
• Klassic suggests Loctite 270 (green I think) for head studs.

Prepping to assemble our 1970 914-6 engine (aka 1969 911T).

Thanks.

[stownsen914]

You'll get a different opinions on this, but for many critical fasteners like head studs and con rod bolts, most don't use thread lock. I'm aware the Bruce A. recommended red loctite for head studs. It would be interesting to hear from any pro builders who do this today. Thread lock is great stuff, but for some fasteners it can't help you, and could actually hurt.

Rod bolts don't fail from just coming loose, they fail structurally or stretch, and then all hell breaks loose. Thread lock won't help here.
For head studs, some say to use thread lock when installing the studs into the case. Thing is, it's important to tension a fastener when using thread lock, or you risk it setting improperly. And then ironically once exposed to heat and stress, the thread lock can break down and cause the assembly to generate a small clearance and loosen. I'm definitely not good enough to assemble an engine fast enough to tension head studs before thread lock would set (set time is like 20 mins). I'm not aware that head studs backing out of the case is a problem anyway?

One place that thread lock IS a good idea is some 911 models, notably 2.4-2.7, when revved to 7500 or more, need thread lock on the flywheel bolts. Most recommend red.