Hirth coupling: greased or not?

Leonard Zinn says "no", Daimeon Shanks (Garmin wrench) says "yes" (scroll up to "1").

The internet in general is evenly split.

I've ruled-out all the usual suspects and all that's left is the coupling as the source of a metal-on-metal, creaking/splintering noise, that is directly related to how hard I'm pushing the cranks, both on and off the saddle.

I had exactly the same noise with the previous alloy cranks, now got the same with freshly installed crabon: fitted by me, torqued by LBS.

It's something else creaking.

Well it doesn't seem to be a common problem, but I'm stumped as to what else it could be.

Recently rebuilt and the only "original" parts are the frame, wheels, pedals, seatpost and saddle.

Creaking is the same on or off the saddle, so that's out; creaking varies depending on how hard I'm pedalling: only silent when I'm not putting any pressure on the pedals and increases the harder I push.

Exactly the same problem as before the rebuild.

I have UT on two bikes and have had lots of noise from alot things, but never the hirths. I'm a non-greaser. And hand-torquer...
My guess would be around the pedals/cleats/shoes area. Often overlooked.
Unthreading bb cups are a common problem wit UT, maybe that can be noisy.
You could always just try to grease the joint and see if it helps and clean it off again if it doesn't.

Cups are "hand tight and Loctite", but I'll check the pedals and cleats.

I'll have another wheelset ready tomorrow so I'll be able to rule that out too.

I would try greasing the coupling, but it's an LBS job to get them torqued-up as I don't have a big torque wrench.

UT bearings tend to rattle around in their housings, as they are press fit on the axle but slide into the cups, the opposite of other BB types. The Hirth joint itself shouldn't be anywhere near moving if it's undamaged and correctly assembled, there's about 10 tonnes of preload pressing the two halves together.

It is distinctly (hard) metal-on-metal though, not what I'd imagine with the (soft) cups: reminds me of a sinking ship, when the pressure crushes the hull.

I'll swap-out the pedals/cleats/shoes, as I can't imagine even my LBS being unable to use a torque wrench...

It's not the Hirth joint. I'd imagine, although happy to be corrected, that the only reason you'd have for greasing it is to prevent the two halves chemically bonding together? In which case anti-seize would be better.

In which case anti-seize would be better

Don't put powdered copper or any other colloidal lubricant in your Hirth joint

Copy that. Mine - Specialized lightening crank - went together bone dry with just a spot of grease on the retaining bolt.

Mine was installed dry and has recently developed a "tick" on each half rotation when I'm out the saddle. Not had time to investigate yet. Assumed it might just need tightening. I think I just greased the threads.

Tester, could you offer so more info on the anti-copaslip stance? Always nice to learn something!

Tester, could you offer so more info on the anti-copaslip stance?

I think the lumps of copper in Copaslip are big enough to be a problem given the geometry and tolerance of the mating parts. Whereas a coarsely toleranced screw thread will effectively pump the grease out of the flank contact area, the mating of the Hirth joint is, to a 50μm blob of copper, more like a testicle getting squashed between two bricks - it cant run away fast enough, and there is no relative motion between the faces to drive it. You end up with small flattened copper plates stuck between the steel teeth.

You don't need any kind of protection against galvanic corrosion at the joint interface, since there is no dissimilar metal contact.

If you use a lubricant on the teeth which can be squeezed out (oil or clear grease), it won't be doing any lubricating when lubrication would have any effect. If you use a lubricant which can withstand the very high pressure, it's stuck between the mating faces compromising the joint.

Daimeon Shanks (Garmin wrench) says "yes"

He also says you have to slide the bearings onto the half axles. If you have to replace UT bearings, they are a press fit on the axle and have a retaining circlip which he completes fails to mention.

Point taken: I just wanted to highlight the differing opinions (having failed to find a definitive answer) and quickly Googled his bona fides.

is there a " should i grease this part " thread ?
i was unsure about a cog on a track hub the other day would be nice to have a definitive thread
listing intersections and state yes or no or grease copper slip or naked

I don't think so: sounds like you've just volunteered yourself...

Good idea. I'm never sure about cranks. Should I be... I'll just make the thread.

to grease or not to grease that is the question

to grease or not to grease, grease is the word

Thanks for that, makes a lot of sense. Basically the joint makes a solid axle. Copper particles are almost like an imperfection!

Although I can't get the testicle analogy out of my head now.

I can't get the testicle analogy out of my head now

That was the intention - give you something memorable to remind you of what the answer is :-)

UT can do two noises, which sound the same and are either bearings or chainring bolts which need tightening. The coupling is solid if the bolt is tight

Are you sure it's not your rear QR shifting?

Nutted axle, fixed innit.

Cups and bearings are near new, chainring bolts are threadlocked.