When installing front fork mount and rear racks, and bolting into the braze-ons, (such as Blackburn racks) are lock washers necessary?

Use blue Loctite.

The front ones need to be removable. They only get installed when needed.

Blue & Green Locktite still allows normal removal. RED, takes a lot of heat to remove.

Often you'll see small threaded parts with Blue from the factory if you were to look.

lock washers work by DIGGING INTO the contact surface... they can and do ruin aluminum parts they get smashed into.

use the blue locktite..
bicycle disc brake rotor and mount screws come with blue on them.
another thing i've used in high vibration situations is Permatex2 gasket tar... it remains tarry and will hold a bolt/nut/screw in place until you want to remove it... but the removal is similar to red locktite... very slow and needs lots of force.
the radiator mounts, exhaust and engine mounts on my Super-Mod Odyssey ATV Demanded use of Permatex2.

Thread locking adhesive ("Loctite") is easily undone by heating the fastener with a soldering iron.

If you want a lockwasher that doesn't dig into the surface, and works better, get a Nordlock; Two washers with facing wedge surfaces, as the bolt tries to unscrew, it tightens due to the wedges. I had a first gen Dahon folding bike with a folding crank that the bolt was always coming loose, regular lock washer didn't help, a Nordlock worked.

I agree with blue loctite being the best solution if you want some peace of mind but if you're removing and replacing the rack occasionally, I find there is no need for anything other than bare or greased threads as you will be tightening them regularly. I only use grease for fender and rack eyelets and haven't had a fastener come loose in decades and no stuck fasteners from corrosion.

"lock washers work by DIGGING INTO the contact surface... they can and do ruin aluminum parts they get smashed into" maddog34

Not completely correct. Lock washers also provide a spring like aspect to the fastener to handle the slight loosening that stresses and vibration produce in the installed bolt.

"Lock washers are special types of washers that prevent fastened parts such as nuts and bolts from loosening due to vibration and rotational forces12345. They provide a spring force or friction between the fastener and the assembled part, thereby maintaining tension and keeping the fastener tight." some quote from a online search so must be correct Andy


I should have offered an answer for the OP's question- I do like to add flat washers (not locking ones) to my accessory fasteners when possible. Especially when the accessory is Al (and this is when maddog34 is correct) the flat washer reduces the wear on the accessory bolt hole's surface and makes tightening the bolt a bit easier to do. I have seen far too many split and star lock washers that are deformed, pried open or broken on the M5 and M5 bolts that most bikes use for these functions. What i dislike about thread locker is that so many people want to just forget about doing the periodic maintenance that keeps a well assembled bike working trouble free, and they believe thread lockers are the best "head in the sand" solution. Andy

Most people who do their own maintenance just might overtighten fasteners, deforming the locking washer.

...and possibly stripping the alloy threads. Watch the torque.

I do like a good spring washer.

My favorite spring washers are completely smooth, but are "wavy", so they provide the "spring" without chewing up the alloy.

How about using Nylocks? You can reuse them a number of times before they degrade.

please post evidence of the existence of nylock SCREWS.

Reality time... i regularly see Over-torqued screws on racks... i have, on many occasions, seen BMX rear axle nuts and split Lock Washers tightened to the point of pulling threads.. the dropouts are sometimes totally eroded by the split washers... i also see non-flanged nuts tightened onto aluminum dropouts... i've scrapped a couple alu. frames because of such erosions...
Flat washers indeed help distribute the forces involved, but most bike owners forget them or don't re-install them... sad but true.
Cross threaded American nuts show up on Metric axles occasionally... the axle and nuts need replaced... i keep a big plastic Skippy jar of rear axle nuts here, and about 30-40 solid rear axles, many with complete hardware and cones..... 100 serrated flat washers sit at the ready in one of the small parts organizers drawers... the serrations always face towards the nuts, NOT the frame
most walmart bikes come with no washers, just a serrated flange nut... many show ample indication of Vise Grip use... sigh.

split washers are for more or less permanent installs... they are metal-ripping destructors as the nuts are removed.
a large burr typically forms, that then needs removed.
the spring force you mentioned forces the face of the cut into the metal... twisting the nut to remove it causes the destruction to begin.
star lock washers tend to dig in less, in multiple spots.
they get used as ground point improvement aides around here, mostly... with a smear of Di-lectric grease.
old car revivals, car stereo and acc. lights come to mind....

Do people ever have problems with rack screws backing out at all? I haven't seen it.

Since you asked:
https://nylok.com/pre-applied-proces...-pellet-strip/

cool! now... where can i buy M5 x12mm button head allen screws, in nylok style, and how much in a lot of 100?

Not Nylock brand, but same principle:
https://accu-components.com/us/socke...tate=pg:2/ct:r

Yes, rack bolts are often loose. One reason i see too frequently (or did when i was full time wrenching) was poor rack strut/brace/extension alignment WRT the frame's mounting boss. Many bikes have these bosses at odd angles (think upper seat stay mounts as example) and/or have no true flat surface for the brace/strut to seat against. How many rack installers take the time to bend the, usual, 4 mounting brace ends with what the frame most wants? very few I have worked with do and many of the known home install jobs I see are nearly never tweaked as could be to fit best. In time the not really well seated rack ends will see more bolt loosening, it's hard to get good torque when the last bit is bending rods and strips WRT the frame mounts.

As an aside or tangent we could talk about another hate of mine... bosses that are not truly a part of the frame (Rivnuts). Andy

I forgot in my post above, the best solution:

On my rack mounts, I use long enough bolts to stick out the other side. I started this because a bolt sheared off (the LONG one below, probably because it loosened first, so then big bending load) and I could just barely back it out with a dental pic; With bolt sticking out the other side, it's easy to extract. BUT ALSO, I then put a plain nut (stainless steel, like the bolt) on the far side, slight torque, and if bolts were to ever loosen before, then won't now. Further, I use anti-seize on the threads, and, once torqued, put a dot of red nail polish on the 12 o'clock (top) position of the bolt head, so I can see at a glance if the bolt is coming loose. And I carry spare bolts. This is my recommendation for loaded touring bikes, better than loctite, because there won't be a soldering iron in the field to soften the locktite, though a torch lighter would probably work. An assortment of long rack bolts, M5 sockethead stainless, 5 lengths with 5 or 10 each length (can't remember), was like 7 or 8 dollars on amazon.

Nylok type fastener locking designs do have an issue that most here might not consider, they don't like much reuse. As long as the locking insert has rebound ability and can equally recompress on reuse there's no problem with reusing these. But with each assembly the insert does loose some effectiveness. So to over time as the plastic dries out.

Think about a rack install where you might dry fit the rack a couple of times or more (especially if fenders are in play) and using the same nylok nuts. The end fitting could well end up with a significant loss of locking ability. Just one more reason to consider these thread locking things as the suspenders to the belt of good fit up and torque. In my view thread locking is secondary to good fit up, yet I read so much mention of thread locking stuff and so little about assembly alignment. Andy

My understanding of wave washers is that their application is for bearing/shaft preload needs, not fastener needs. Coming from an adjustable bearing preload past I'm not drawn to these wave washer preloading designs. Andy

Seems like split washers are the usual.