I made an article about this:
How to install square-taper cranks
I also made a video:
A comment in the video's comment section is very good in terms of showing a common situation (and gettin many,
but not all things right - and that's a crucial "but")! I wish to save it (original commenters or YouTube sometimes make comments disappear).
I'll put the comment in quotes, and keep my replies without the grey quote (that can be expanded to read the entire comments,
they are worth reading even if not completely correct).
VIEWER:
Take this guys comments as opinions and not necessarily facts.
I wrenched for decades on square taper setups and personally I was taught differently that you never grease the tapers or the arms before fitting. There is much debate on this but when they are both clean and dry they will literally form an airtight seal once they are installed. That is why you need a puller to get the arms back off. You literally should not even need crank bolts to retain the arms once they have been tightened initially correctly and then after again after your first few rides. There used to be a whole market for lightweight straight aluminum crank bolts to replace the steel ones. You would take out the steel bolts and just hand tighten the aluminum ones as they would shear off tightening with a wrench and these had no holding power at all.
The biggest issue I would see is that if you remove and install you tapered arm too many times the softer arms will deform some each time and they can start to bottom out (the angled axle taper slides too far into the softer arms). This will prevent the proper tight fit and the arms can start rocking on the taper ruining the crank arms. Phil Wood used to make over sized taper bottoms so that you could continue to use your arms once they started bottoming out on normal sized tapers.
As he mentions it is important to clean out the bottom threads before installing a new bottom cups. They might be full of dried grease or even Locktite depending on the brand or previous installation method. I used a Dremel tool with a wire brush and then an old tooth brush and just go around the threads until they are clean and then wipe then down with a rag. Be careful running your fingers around the threads as they can be very sharp and slice your fingers open.
At this point if the threads are really clean you should be able to easily hand thread each bottom cup all the way in. If you cannot then the threads are not clean enough or they are damaged and should be re-threaded by a local shop.
In order for the bottom cups on any system (tapered or not) to really work correctly the should be parallel to each other. That is why your bottom is faced with a tool to make parallel surfaces on each side. With a cartridge bottom the the bearings are internally parallel already but if the metal frame faces are not clean the cups might not fit flush to the frame when tightened which can cause creaking when pedaling. Grease or Anti-seize helps but you should not have left over paint or crud on the bottom faces before installing the cups. His shell facings were not clean but it probably would not effect his installation.
Bottoms as he mentioned come in many different axle lengths and also shell widths. Road bike frame bottom shells usually are 68mm wide and Mountain bike
shells are usually 73mm wide. You need to measure your frame shell width to make sure you get the appropriate bottom (even with the correct axle length). Some bottoms are designed to handle both shell widths and come with appropriate alignment spacers. If your right crank arm is too close to the frame you can place one or more spacers under it to move the bottom cup farther out which move the crank arm out as well.
Normally you would not have so many threads showings on the left adjustable bottom cup once it is finally tightened down. Makes me wonder if he is trying to put a 73mm Mountain bottom in a 68mm Road shell even if the crank arms are centered on the frame.
I recommend installing the right bottom cup and crank arm first. Then tighten up the left bottom cup until you can feel no play anymore. You check the play by aligning the right crank arm with the frame seat tube and pulling and pushing the crank arm towards the frame. If you feel any movement then tighten the left cup until the play is gone. If there is still play after the left cup is tightened down tight then you are probably bottomed out on the right taper and it is rocking on the axle which means your crank arm has issues. Some bottoms have a left side retaining ring you thread on to prevent the bottom cup from moving after you have it adjusted correctly. Then I install the left crank arm last. I then check both cranks arms one last time for any play as they should be rock solid at this point.
When finished and you look down between the frame and crank arms you should still be able to see some taper on the axle showing where it enters the crank arms. If no taper shows anymore you are getting close to bottoming out the arms and they might start to rock and come loose out on the road. I always check the crank arms bolts after the first couple of rides and make sure they are staying tight. Once they stay tight as mentioned above they are no longer actually holding the crank arms on and can be replaced with lighter non steel ones.
I have no issues with using Grease or Anti-seize on the bottom cups (especially if you have a Titanium bottom shell) or on the crank bolts, I just would never put any on the tapers or crank arms. If you do put some on the tapers or crank arms use as little as possible not the large amount he used.
As he showed always remember to place any existing chain over the bottom axle before installing the right crank arm. You do not want to have to remove the crank arm or break the chain to correct the issue if you forget.
For the technical minded they are different type of axle tapers as well that need to be matched to the tapers in your crank arms or the internal taper angle will be wrong. If you stay within brands you will be fine but if you go with a third party bottom square taper system (and there are many with some much more expensive, better designed, and longer lasting than stock ones) be sure to get the correct model for your specific crank model.
BikeGremlinUS:
Some very good points, some mistakes.
1. Regarding the (famous) "you state your opinions as facts":
https://bike.bikegremlin.com/17645/cycling-industry-nonsense/#6.2
2. Regarding the bolt function and whether tapers should be greased (hows and whys explained):
https://bike.bikegremlin.com/17055/how-to-install-square-taper-cranks/
EDIT:
The rest of the comment is pretty much spot-on.
Relja
VIEWER:
@BikeGremlinUS Regarding #2 Like I said there is much debate on whether to grease tapers. A simple Google search on whether to grease axle tapers will find dozens of threads and articles with different opinions from many mechanics with a long history of working on tapers. There are as many that think it is a bad idea as there are that think it is a good idea and many taper vendors do not mention grease at all in their installation instructions. Those that think you should grease usually say to use as little grease as possible if you do.
By re-tightening the crank bolts after each of the first few rides you are taking care of any additional movement of the crank arms on the tapers and the initial installation from pedaling The crank arms then settle in place and cannot be tightened after this point and the arms are locked in place and bolts could even be removed.
There are thousands of mechanics that were taught this method and used it without issue for decades and numerous vendors that also recommend this method. Your referenced article is just another opinion without stating any underlying reference materials to substantiate their claims.
Do as you want but there is no clear cut answer on this subject and I have installed hundreds of tapered bottoms without grease with no issues. Just double check the bolt tightness after the first few rides until they settle in place. Personally I have seen numerous crank arms damaged because they slid to far onto the tapers when tightened and any taper lubrication is just to make that easier to happen.
BikeGremlinUS:
There are thousands of split cranks (and dry fit myths) that most probably (and that part about probability is my opinion) originate from the practice of re-tightening the crank arm mounting bolts.
As I've tried my best to explain in the article (if you read it, you should see the bolt tension change addressed and explained too). Quote (note that English is not my native, so if you really read the damn thing and didn't get it, it could be due to my poor explaining):
"This will effectively reduce the bolt’s preload. If the crank was properly installed, the preload loss will not be big enough for the bolt to become loose and unscrew. But the bolt will be less tight than before the first ride. You could take a 40 Nm torque wrench and further tighten the bolt (but you must not do that!). If you do that, continue riding, then tighten the bolt to 40 Nm again – you will eventually split the crank."
You are free to disagree though.
VIEWER:
@BikeGremlinUS I just double checked my old green Sutherland "Book of bicycle mechanics" which used to be the mainstay tutorial and reference for mechanics in local USA bike shops. It specifically states to make sure you "clean and de-grease both the axle tapers and crank arms before assembly so that they dry fit". This is how we were taught back in the 80's and millions of bikes were assembled in that manner.
My expert in print against yours. Just point out that that there is disagreement on this subject and let people decide themselves....
BikeGremlinUS:
They got it wrong. They are humans. Ask them about an update to confirm their stance.
Edit, to make it clear what I mean (again, English is not my native, so I usually need more words):
They got it wrong. That happens - experts are human.
If in doubt, reach out to the original publisher and ask if they still stand by that recommendation today.
Mechanical interfaces like square tapers don’t care about tradition (or even publisher reputation), they follow physics.
That’s what I based my article on.
