Grease a square taper spindle, yay or nay?

[Ajax Bay]

Always I have lightly nipped up, backed of the nut/ bolt, a light tap with a block of wood & mallet on the crank ,then tighted up , being a taper fit gives it the grip, but it can be too tight.

Why would you "back off" the nut/bolt? I make it tight, tight; then welly the crank at spindle end (obv) (wood support on other side) with a mallet and then final tighten (50+Nm in theory).

What would be the symptoms of an overtightened crank bolt? I'm assuming that if you keep tightening it won't actually move the crank any further up the taper?

In use, by design the crank will 'climb' up the tapered spindle. But no further tightening is needed: the bolt cover will stop it; if no bolt cover tighten gently so it stays in or remove bit of threadlock and screw back in but no force(torque).
If you carry on heavy tightening and riding an repeat in extremis you will break the crank (see @ColinJ 's image).

I don't know what caused this problem of mine - overtightening, undertightening...?

For mechanism: see comment above. So if bolt has been consc(ient)iously retightened, I'd say @overtightening. Otherwise (and more likely) cranks mainly fail this way for other reasons (stress riser etc possible cause undertightening, crank loosening and carrying on riding when "there was something wrong", and powahh).

I'm not really sure that I would describe a taper fit as an "interference fit".

I think @grldtnr describing this as an interference fit is technically correct and only marginally useful.

 

[andrew_s]

I don't know what caused this problem of mine - overtightening, undertightening...?

View attachment 633061

I'd suspect it was repeatedly tightening a crank bolt that had appeared to loosen a bit.
On initial fitment, the crank bolt will break before the crank, but in use the crank will flex and lever against the bolt, walking up the taper a bit. If you then snug up the bolt, it will walk a bit further, and with repeated tightening will walk far enough to split.

I always use a small smidgen of grease, tighten as much as I can with a 10" adjustable, then leave it alone until it comes to removal.

 

[andrew_s]

in relation to square taper i always put grease on the inside of the non drive side cup as on a number of occasions i have had mysterious creaks that originated from there .

I've had failure to grease the inside of the NDS cup result in the cup seizing on to the cartridge tight enough that the fixed drive side cup (with the flange) ripped off the cartridge when I uncrewed it, with the cartridge coming out the wrong side of the frame (UN72).

 

[Twilkes]

I've had failure to grease the inside of the NDS cup result in the cup seizing on to the cartridge tight enough that the fixed drive side cup (with the flange) ripped off the cartridge when I uncrewed it, with the cartridge coming out the wrong side of the frame (UN72).

Sorry is this all to do with just the BB, or attaching the crankset to the BB? I'm starting to think I've missed a cup somewhere...

 

[Ajax Bay]

No @Twilkes, ck branched out into smearing grease on the threads of a BB shell and Andrew took it on from there, sharing their BB 'experience'; but , hey, this is CycleChat.

 

[grldtnr]

If you grease the taper , it will never be tight, movement will cause it to eventually fail , the taper on the crank will fail , i.e. come loose.
As long as the assembly is clean ,with no containment of grease , it shouldn't sieze on, I have never experienced a failure like that, and I used to service Royal Mail Postie bikes as my duty , they were fitted with steel cranks not ally.
It's what I do, I believe it isn't an issue, I have had more problems off siezed pedals , seat pins ,& stems, in my time, but all bikes through my workshop, always had pedals greased, seat pins & stems as well, same thing greased then wiped off, regular maintenance, prevented siezures, but then I was looking after 250 bikes!

 

[SydZ]

I always put a small amount of grease between metal contacts as, until I know otherwise, assume they are dissimilar metals and may lead to future problems.

 

[Blue Hills]

If you grease the taper , it will never be tight, movement will cause it to eventually fail , the taper on the crank will fail , i.e. come loose. As long as the assembly is clean ,with no containment of grease , it shouldn't sieze on, I have never experienced a failure like that, and I used to service Royal Mail Postie bikes as my duty , they were fitted with steel cranks not ally.

I've never had one fail yet and I grease. How does this "never tight" thing work? - the crank keeps on going inwards, for ever? Or it somehow backs off? I grease, tighten, after next two rides or so just check it, tighten more if needed.

Mind you the power output of those posties is a thing to behold.

 

[Ian H]

Campagnolo advice putting a small bit of grease on the taper and then giving it a wipe with a rag so that most of it comes off albeit a thin smear.

I do that with all makes and have had no problems.

I'm content to follow Mr Campagnolo's advice. Ordinary grease is fine.

 

[T4tomo]

Definitely not! It is a interference fit,a hard surface/ soft face , as best has qouted up thread, a good clean, a very light smear of grease then wiped off.

If you grease the taper , it will never be tight, movement will cause it to eventually fail , the taper on the crank will fail , i.e. come loose.
As long as the assembly is clean ,with no containment of grease , it shouldn't sieze on,

I think you have confused & contradicted yourself?

a light smear wiped off is a light smear.

which is what most people are advocating. its what I do

 

[Andy_R]

If you grease the taper , it will never be tight, movement will cause it to eventually fail , the taper on the crank will fail , i.e. come loose.
As long as the assembly is clean ,with no containment of grease , it shouldn't sieze on, I have never experienced a failure like that, and I used to service Royal Mail Postie bikes as my duty , they were fitted with steel cranks not ally.
It's what I do, I believe it isn't an issue, I have had more problems off siezed pedals , seat pins ,& stems, in my time, but all bikes through my workshop, always had pedals greased, seat pins & stems as well, same thing greased then wiped off, regular maintenance, prevented siezures, but then I was looking after 250 bikes!

Steel cranks, and steel BB spindles don't need grease. But if you have alloy cranks on a steel spindle, grease can help to prevent galvanic corrosion (where they effectively end up "welding" themselves together). This is commonly seen in alloy seatposts in steel frames, but is also sometimes seen in crank/BB combos too.

 

[grldtnr]

Steel cranks, and steel BB spindles don't need grease. But if you have alloy cranks on a steel spindle, grease can help to prevent galvanic corrosion (where they effectively end up "welding" themselves together). This is commonly seen in alloy seatposts in steel frames, but is also sometimes seen in crank/BB combos too.

Hence the procedure, when I took over the maintenance regime, I rarely had problems, obstinate ones had a motor style puller employed the 3 legged type, really stuck ones the angle grinder & cold chisel, parts were supply no probs.
My own bikes , I used the grease free regime, cleaned down with acetone, grease free, and regular tinkering no problems.

 

[Twilkes]

Do square taper cranks suffer any from regular removal/replacement? My old BB30 crank I had to whack out with a hammer so once it was in place I tended to leave it there!

 

[Blue Hills]

Do square taper cranks suffer any from regular removal/replacement? My old BB30 crank I had to whack out with a hammer so once it was in place I tended to leave it there!

don't think so - not if you are careful.
The BB itself should be taken out every so often, threads cleaned and greased - put back in - the things (or the old ones) are so dependable that if left they may seize in. I'd always take out the ST BB on any newly acquired bike and do this. Need to be careful not to crossthread when putting back in - surprisingly easy to do.

 

[Ajax Bay]

I think the risk of finding a square taper crank stuck (cannot be removed with a crank extractor tool) is extremely low and pales into insignificance compared to the significant risk of the bottom bracket being a bar steward to remove from its shell.
As @grldtnr says "I rarely had problems" and on his own bikes "used the grease free regime".
Given the fit mechanism of square taper, grease on the interface will make no difference, but as I said in my first post, grease will do no harm.