Lock washers

[Randy Webb]

Anybody know the proper uses of:
1. wavy washers,
2. split rings
3. star washers
??

I know there have been threads on when PAG tended to use one over the other, but is there any real rule other avoiding marring of the surface?

[ChrisBennet]

That's a good question. The only place I recall finding split ring washers on my '86 is in inside the transmission.
As I recall the late Carrol Smith did not have a high regard for split ring washers.
-Chris

[Formerly Steve Wilkinson]

Add to the list the narrow, non-wavy (but same size) washers you find on a 911 that have the serrations all the way around.

Stephan

[Randy Webb]

Steve - I deliberately left those out - they are called (in the US) Belleville washers I think and are only used on the CV joints (?).

Do you feel another book coming on? .... Secrets of Porsche Fasteners?

[Schrup]

I could be wrong, but it seemed to me that there were some Schnorr (brand name) washers on some of my spring plate fasteners.

[Zeke]

Over the years I have just gotten a feeling for washers and German cars.
Wavy: Between bolts and nuts on studs where the object is fastened to alloy.
Split: To steel.
Serated: Where diameter is a factor.
And, last, aluminum: Nothing but alloy involved, i.e., trans and engine case.

I'm sure there are numerous exceptions such as the rear seat pivots that take the wavy. The function there is to provide tensioned spacing after the shouder bolt bottoms. Use 'em as you see the best application. For instance, a split on the engine tin just digs in and where any holes are elongated, the split may fall in the slot making a lock washer ineffective. A split on alloy digs in making a mess. And so on.

[Randy Webb]

Zeke - so overall, it's all based on surface characteristics? Not on the amount of tension on the bolt?

[Zeke]

Originally posted by Randy Webb
Zeke - so overall, it's all based on surface characteristics? Not on the amount of tension on the bolt?

At least in part, that's what I think. I tend to go with logic and common sense before engineering specs. Why? Because so far, it works. If a lock washer is digging into the metal, one could argue that it's getting a "bite" while another could argue that the digging is compromising the hold of the washer. Rather than argue the issue, I'll consider the practical aspect of the application.

Another way to do that particular application is to install a flat washer against the alloy and a split lock washer on top. But that's 2 washers, which is seldom seen in production.

Note: Above all, I think proper torque is more important and a washer appliction is simply designed to maintain the torque. Frankly, I'm not so sure I want to depend on the washer for the tension as much as I believe the whole package is what is needed.

I'm open to learn. Whatcha got?

[Randy Webb]

I got nuthin'. I generally do what Porsche sez (or did) unless I know it was a bad idea (e.g. rod bolts, the entire electrical system, mid-70's exhaust systems).

Jim Simms may chime in... esp. if he has a bot that scans for his name in threads (unless I mispelled it -- Sims).

I'd suspect that the washer doesn't have much to do with tension on the bolt except to spread the load.

My original thought (while organizing metric hardware the other day) was: why not just dump everything except the wavy washers for general use (not CV joints).

BTW, I've noticed a lot of the Wurth flat wshers are just cheap cut washers with a bit of flashing still on them.

Shrup: -- The PET would be the place to check on that. I've forgotten what I found on mine when I upgraded them.

[TimT]

As I recall the late Carrol Smith did not have a high regard for split ring washers.

ya.... tighten down on a split washer and watch it open up...the washers on the dif have a locking feature where you have to peen over a tab to lock the bolt in place... way more specialised than a regular split washer

The washer is usually just to prevent galling between the hardened (nut or bolt) surface, and the surface being tightened against.

I like the serrated washer, and wavey washer..

I have a paper somewhere that discusses washere in length... Ill have to try and dig it up....

another type of washer that is useful is a belllville washer... its slightly coniucal shaped, and is avaiable in specific tesnion ranges...

[2.7RACER]

FASTENERS, which by the way includes all of the various "lock washers" is a subject deserving of much study.
I'm upset to hear Carroll Smith is no longer with us.
I learned more about nuts and bolts reading his book "ENGINEER TO WIN" than I thought possible.
This book may be available from our gracious host Wayne. Well worth the read for those of you who may be interested in the real engineering behind the science of fasteners, plus many more subjects of interest for those building race cars. Or for that matter any machine subject to the rigors of stress and vibration.
Page 151 of his book has some insight into his opinion about lock washers. The entire chapter is about threaded fasteners. Believe me once you read it you can never take a simple nut and bolt for granted.
He talks about elastic stop nuts as being most useful for all but high temperature aplications.
If there is another book out there that covers this subject of fasteners, that is readable for those of us without a M.E. I would certainly read it.
After all we are all aware of the issues with the various case studs used to hold our motors together, rod bolts that can only be torqued once, flywheel bolts that must meet very high standards to stay together, the allen head cap screws used to fasten the CV joints to the transaxle and drive axle, the nuts and bolts used to fasten the exhaust system.
All of the above have a tremendous amount of engineering involved.
Me, whatever I can learn just adds to the fun from playing with these wonderful toys from Stuttgart.
That's my .02 cents.

[Jim Sims]

Under severe vibration or alternating load conditions almost all common lock washers (helical split, toothed star - internal and external, wave or spring, simple Belleville, etc.) are nearly worthless. There is especially poor performance if a flat bearing washer is used under the lock washer as the nut or bolt, lock washer and bearing washer just turn together and unloosen. Under mild conditions these common types do okay but beyond that something else should be used. The toothed or serrated Belleville (Schnorr) washers (in good condition - serrations not worn) do reasonably well in severe vibration conditions - there are tests to back up this claim.

Better fastener locking is obtained from a prevailing torque feature (distorted thread geometry, a plastic insert, etc.) or from washers and nuts or other appliances that have features that engage both the nut or head of the bolt and some other item or from locking compounds that cure and bond the threads together. Then probably best of all is lockwire or safety wire and items like cotter pins or transverse locking bolts or screws.

I note that on many of the important 911 applications Porsche has used fasteners with prevailing torque features. Plus Schnorr washers were used on CV joint screws (consider the two screw washer plate used - it can't rotate and defeat the locking of the Schnorr washers) through the early 80's and on the spring plate bolts. Beyond these more important joints I see no obvious pattern to OEM Porsche lock washer application; on my cars I tend to use what the factory parts catalogs indicate.

Note that flat bearing washers are important to use under the the fastener (either the screw head or the nut) being turned to tighten the joint to keep the torque value obtained more valid and to avoid digging into the surface being secured.

Cheers, Jim