locking washers

[tahoe healey]

When is it appropriate to use one kind of lock wisher over another, split rings, star or inverted star? And is using lock-tight in addition like suspender with a belt?
TH

 

[roscoe]

If authenticity is not an issue, I like the star washers more than the split washers. Both are used in the aviation industry. Neither should be reused without careful inspection to make sure the locking features still function. The split washers flatten out as do star washers. It seems to me that star washers have more area that actuallly grips as compared to split washers. Often what you see is a bolt with a star washer under the head, and then a plain washer under that so that the star doesn't cut the surface the bolt is threaded into. By all means use a Loc-tite product if it is not something you remove but once in a blue moon, or if it is a critical fastener that has bad consequences if it comes out. Don't forget there are many varieites of Loc-tite products that are designed for different needs. A little goes a long way.

 

[suprgnat]

From NASA

https://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1990/RP-1228.html
"The lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a lockwasher of this type is useless for locking."

In the interest of originality, I plan to use the original fasteners and Loctite.

or

Naval Ships' Technical Manual, Chapter 75:
"Although lockwashers may be encountered, using the flat washers with selflocking nuts, self-locking fasteners, self-locking inserts, or thread sealants such as MIL-S-22473 anaerobic compounds is preferable.

If loosening has been a problem, however, replace the lockwashers with self-locking fasteners.

 

[Michael Oritt]

"From NASA

https://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1990/RP-1228.html
"The lockwasher serves as a spring while the bolt is being tightened. However, the washer is normally flat by the time the bolt is fully torqued. At this time it is equivalent to a solid flat washer, and its locking ability is nonexistent. In summary, a lockwasher of this type is useless for locking."

----------------------
Then why do they call it a lockwasher?

 

[suprgnat]

Quote (ASME B18.21.1):
"The word lock appearing in the names of products in this standard is a generic term historically associated with their identification and is not intended to imply an indefinite permanency of fixity in attachments where the fastners are used."

 

[Johnny]

Since evereyone seems to have an opinion on this issue please let me chime in with mine. Recently I've been rebuilding the transmission on my BJ7 and have encountered many things I don't like. One of those things is when dismantling the bellhousing from the transmission the bolts holding the bellhousing all were LOOSE, I mean one or two of them I could literally turn by hand. All the bolts had split lockwashers under the bolt heads, and the threads were coated with something, kind of sticky. Also, on the OD adapter plate that bolts to the transmission I found all those nuts had split lockwashers and they too were very loose. I've concluded that split lockwashers do not LOCK anything. I'll use internal star washers (only because they look more like standard washers when tightened down) with self locking nuts (nyloc)and lots of thread sealant on all. Hopefully I'll never have to remove any of the above.

 

[Bob_Spidell]

The late, great Carroll Smith from _Nuts, Bolts, Fasteners and Plumbing Handbook_:

"Neither the spring washer nor the wave washer do anything worth talking about--other than to provide the user with a false sense of security ... Once compressed, the spring washer is nothing but a flat washer." And: "I consider the tab washer to be an idiot device" (of course, they are used a lot on our LBCs).

Have made a study of this myself. I never use spring (split) washers on aluminum parts--hardened ("grade 8") washers under the bolt head with Loctite works well (the greater diameter of the flat washer provides more overall clamping force). This has worked flawlessly on my front shocks--torque to spec--and elsewhere (like carb studs). On the rear shocks, however, I tried using flat washers on both sides with no split washers, but the bolts loosened. Now, I have hardened flat washers under the bolt head on the shock side, with a split lockwasher under the nut on the mounting plate side with Loctite on the bolt threads. No loosening.

I agonize over how to fasten parts--it seems mundane but is critical (in the case of steering, suspension, brakes, etc. your life could depend on it). I use Loctite liberally--Smith loved it--except where I use antiseize.

In theory, a new, high-quality, properly torqued bolt or stud with (maybe) only a hardened flat washer--as used on head studs, rod and bearing caps, etc. is the only way to go, but we can't always get a correct, new bolt or stud and can't always torque exactly--e.g. torque-to-yield--so I use washers and Loctite as appropriate.

 

[Legal Bill]

Silly me. I thought the lock washer provided tension against the bolt head, ensuring the threads of the fasteners were pushing aigainst each other at all times.

 

[pan]

This is an interesting thread. When I was restoring my 100 a few years ago now, I tried to find out when & where to use the different styles of washer.
I thought there must be some kind of basic guideline on this that mechanics might be taught when learning their trade. I asked mechanics who I work with but none could help.

 

[roscoe]

I don't buy the "flattened lock wsher" scenario that is attributed to the NASA folks above. Star washers will flatten out if re-used, and they probably don't do anything after that point. But if a split or star washer still retains it's offset and returns to it's sprung position when torque is released it will have some ability to keep a bolt/nut from unthreading due to vibration etc. I've done torque experiments with a very sensitive torque screw-driver , and found that the release torque is considerably higher with a star washer, than without. To each, his own. Not a substitute for drilled head bolts with safety wire, or cotter keyed bolts and nuts, but not worthless either. I'm also a fan of service removeable loc-tite for many applications.

 

[Bob_Spidell]

Silly me. I thought the lock washer provided tension against the bolt head, ensuring the threads of the fasteners were pushing aigainst each other at all times.

That's OK (I used to think friction between the threads kept bolts from loosening).

The clamping force exerted by the stretching of the bolt--steel is highly elastic--should exert considerably more force than a lock washer except in very low-torque applications. If the lock washer is exerting the majority of force the bolt is not properly torqued/tensioned. Application and installation vary depending on whether the bolt is used in tension or shear.

I'm not an A&P, but I did a bit of work on my own aircraft. I don't recall ever seeing a split lock washer anywhere (I think I might have seen a few star washers on small screws). All key fasteners are safety wired which, according to Smith, is only to keep the bolt from falling out, not to keep tension on the bolt.

 

[suprgnat]

The link to the NASA Fastener Design Manual download page is in my original post. I'm pretty certain that the URL is not being spoofed, so I think it's safe to say the information contained in the PDF IS from NASA :wink:

Paul

 

[roscoe]

Bob, please don't take offense with a difference of opinion. My comments were directed towards the first post in the thread. Lycoming uses split and star washers on many of the bolts that hold the case halves togehter and the oil sump on, on most of their piston engines. Where you don't see lock washers of this type is when there is at least one other mechanism, such as fiber lock nuts, or cotter pins, or safety wire. You find these methods on almost all flight control bolts and nuts. I assume the reason is that they are more effective than lock washers. Don't even ask me about Pal nuts. I like them too, but they are a pain in the rear.

 

[Bob_Spidell]

Oops ... missed the NASA thread entirely. I deleted my post. Apologies for the rant.