Spring/wave washers?

[Mr Beau]

What's with Porsche's decision to use spring washers? I was getting ready to button up the cam tower housing when I realized the PO had flat vs the wave ('spring' in PET) ones that Porsche used.

Safe to use conventional steel washers here? What about other locations?

https://www.pelicanparts.com/More_Info/N0122418.htm?pn=N012-241-8-OEM

[patkeefe]

They are a form of lock washer. In theory, they provide some extra tension to keep the threaded assembly from coming apart. I have never really understood why this is so, as any force applied by the washer is a tiny fraction of the strength provided by the bolt stretching.

Maybe I was sleeping that day in engineering school.

[dannobee]

Here's a video on the performance on different kinds of spring washers, nylocks, and even double nuts on a Junkers Vibration machine. In heavy rail, we now use Nord-Locks on critical bolts. Nylocks WITH a spring washer would still loosen up on the wheel trucks. Steel on steel from the wheels rolling on the rails causes some pretty harsh conditions for fastener tension.

https://www.youtube.com/watch?v=tAQUycabc9Q

[Mr Beau]

I'm just not sure why they're used in 'non-critical' areas like the cam housing. And the amount of tension they would add seems like a rounding error. A couple of the used one in my engine came apart--when's the last time you saw a washer fail??


Some other relevant reading: https://engineerdog.com/2015/01/11/10-tricks-engineers-need-to-know-about-fasteners/

[patkeefe]

Originally Posted by dannobee

Here's a video on the performance on different kinds of spring washers, nylocks, and even double nuts on a Junkers Vibration machine. In heavy rail, we now use Nord-Locks on critical bolts. Nylocks WITH a spring washer would still loosen up on the wheel trucks. Steel on steel from the wheels rolling on the rails causes some pretty harsh conditions for fastener tension.

https://www.youtube.com/watch?v=tAQUycabc9Q

Yup, a regular spring washer is not even comparable to a Nord Lock or a Schnoor. I keep a drawerful of Schnoor washers here at home. I think Bel-Metric sells the Nord Locks.
Nice video, BTW.

[Trackrash]

Another thing to consider with the wavy washers is the fact that they are hard steel and thin. If you replace them with a normal washer that is not hard it may deform. There are also some situations where a thick washer may be too thick for the stud and nut.