Why does my grease cap on the fan hub keep falling off?

[Sarikatime]

Every time while driving my grease cap on the fan hub untwists and falls off. No matter how tight I twist it on it is missing after a tour. How can I keep it on ?

[Daisy Mae]

That's very odd to me...
There should be no "tight" to a grease cup...the function being the cup being packed full of grease where a periodic twist of the cup injects more grease. Being drawn down tight would suggest time to refill the cup with fresh grease....the tension of the packed grease in turn should prevent any movement of the cap.

So, is the cap full to the rim with heavy grease?
Are the threads of either the cap or injector so worn as to enable the cap to easily turn and/or just pop off with little effort?
Is there a crack in the cap (which can lessen thread tension under vibration?)

Beyond that I'm shrugging my shoulders at that mystery...

[Steve Jelf]

The cup, or its cover? Sometimes there is a small spring which keeps the lid from vibrating loose.

[TRDxB2]

Every time while driving my grease cap on the fan hub untwists and falls off. No matter how tight I twist it on it is missing after a tour. How can I keep it on ?

Do you have or did you have a cap/cup like above or an oil cap/cup?

[Mark Gregush]

Are you using one of the modern bearing hubs that would not require greasing? If so, why not solder or glue it in place?

[Sarikatime]

Steve, you are completely right. I have some of those grease cups with the pinchers in the middle and spike in the lid but never knew why so I did not use them. I have lost four or five caps because I did not know. Thank you.

[speedytinc]

Vibration.

If you look @ an original grease cup you will notice a crimped in place leather washer. That leather washer puts enough tension on the cap & keeps the oil from oozing out. From rot , sand /chemical cleaning or wire wheel cleaning will make that leather washer ineffective.
If not to badly worn, they can be recrimped to expand the leather. If your base didnt have a provision for the washer, the cup can be slightly squeezed to tension the threads when reinstalled.

[RecklessKelly]

Mine is just a regular right angle grease fitting pointed opposite of rotation. It has held on for the ride.

[RajoRacer]

Grease cups & grease fittings (ZERK) are two different animals !

[Mark Gregush]

Bit off topic;

Mine is just a regular right angle grease fitting pointed opposite of rotation. It has held on for the ride.

Unless you have unshielded bearings in the housing, grease is not a good idea in this location. There should just be a plug in the hole and use heavy oil like 600W or chain bar oil same as what should be used with kingpins.

[Allan]

If you have a grease cup on the fan, can we assume you are talking of an early fan with the small hub and four riveted blades? I have never seen one of these with the spike and spring holder on that type of greaser.

John's leather "keeper/seal" was likely enough to keep the cap in place originally. It would be nice to be able to replace them, but they appear to be fixed in place by upsets made when the hex was formed above the thread. I can't see any way of replicating this. Perhaps you could put the cap over a wooden broom handle and make a small inwards divot with a centre punch, so that the divot is tighter on the thread.

Allan from down under.

[TRDxB2]

This what was intended for stock fan shaft

[speedytinc]

If you have a grease cup on the fan, can we assume you are talking of an early fan with the small hub and four riveted blades? I have never seen one of these with the spike and spring holder on that type of greaser.

John's leather "keeper/seal" was likely enough to keep the cap in place originally. It would be nice to be able to replace them, but they appear to be fixed in place by upsets made when the hex was formed above the thread. I can't see any way of replicating this. Perhaps you could put the cap over a wooden broom handle and make a small inwards divot with a centre punch, so that the divot is tighter on the thread.

Allan from down under.

Allan, I have replaced a very worn leather seal with an o-ring occasionally.

[Original Smith]

As far as I know, I've not seen the type of grease cup Steve Jelf describes, except for the U Joint.

[J1MGOLDEN]

Frank has the correct answer,

Grease cannot slip into the area where the lubrication is required.

That is why heavy oil rather than grease is required there.

[Allan]

If the fan has a grease cap, it screws onto the back end of the shaft. The shaft is hollow, so that the grease cap will force grease into the void between the two bushes. Oil is for the later aluminium pulleys with the brass plug.

Allan from down under.

[Sarikatime]

I had close to 20 proper grease cups but none with the clips on the inside to keep it from untwisting so I bought 3 from eBay. Thanks Steve.