I have a question about CV Joint bolts

[911pcars]

I can't think of any clamping application that would NOT require a washer of some sort to spread the load under the bolt head. In the case of a socket head screw, there is even less area under the head to distribute the load. Torque would probably be more accurate as well.

I'd suggest using a washer despite what Porsche shows or doesn't show in their parts catalog.

Sherwood Lee
http://members.rennlist.org/911pcars

[island911]

Washers (steel on thick steel) do very little load spreading.

In the case of the CV, I'll say washers are NOT necessary.
Controversial, I know. But you'll have a hard time convincing me that the "spring" of a spring washer is going to help beyond the "spring" in the strained length of the bolt. Also, I've seen how quickly various washers don't help, on vib-table tests.

Proper torque will do . . . safety wire for the extra bit of lock-down.

[Early_S_Man]

Island ... BUT, have you seen any tests using genuine Schnorr washers on DIN 12.9 bolts???

[Randy Webb]

I would consult a good technical refernce on this issue. High end fastener manfs. put out these publs.

Also, I think the dealer told me that PAG used the "moon" shaped double bolt spreader plate thingie's when they did not use round washers on the CV bolts.

[island911]

Originally posted by Early_S_Man
Island ... BUT, have you seen any tests using genuine Schnorr washers on DIN 12.9 bolts???

hmmm. . . come to think of it, I can't remember. I kind of doubt it, though.
Mostly what I remember, is that the best "spring" type washer held on for ~ half a second longer than the worst.

Since the whole idea is to keep the bolt from turning (by keeping the friction up . . .via keeping tension up in the fastener)
I will say the Belleville style washers (Schnorr) are going to perform the best of any of the spring washers. (by far the largest force/range . . . great for short, lower torque fasteners)

Though, even if a Schnorr washer starts to try doing its job (on something like a loosening CV) the axial load will be maybe 200_lbf. (?) . . .I suppose it depends hugely on what size/style, and how many you have in the stack.

So I'm just saying, while they do/can provide outstanding loading for a washer, the load is small compared to the axial load of properly torqued bolt.
So - if the bolt is loosening (even at the high axial load at the proper torque). . . what good is the washer going to do? It will add a bit of life, but not much.

I dunno, but I think the biggest problem on these CV's is not so much from vibration in duced loosening. Rather, (I'm speculating) it comes from poor assembly and torque. If something in the CV assembly stack-up (temporary trapped grease . . .cold-flowing gasket material?) causes the fastener to hit an artificial (or temporary) torque value, then you just have to wait a bit before it's loose. (and this is why re-torquing is common pratice.)

So at the end of this ramble, I'm just trying to say a properly torqued CV bolt (as was done at the factory) can perform just fine.
And, in my 2-cent opinion, If you want extra insurance:
the safest is torque & safety-wire.
The second best, careful assembly with a torque recheck.
Then; Properly sized (for tension) Schnorr washers . . I don't know "how-many of ?-size" would do the trick, though.

Just throwing "a washer" on there "despite what Porsche shows or doesn't show" isn't going to do squat. . . .other than giving fewer threads to be engaged.

[Superman]

I'm curious about this too. My CV joints have the curved plates that each accept two bolts, so a plain washer would be fairly useless. I also have a non-professional-engineer feeling that the stretch of a properly torqued bolt accounts for nearly all the forces necessary for the bolt to stay in place. I also suspect that safety wire and torque checking would be second and third place (not necessarily respectively), and that Schorr washers add something as well. But I'm intrigued by Warren's comment about the findings of test results on Schorr washers. Waiting to hear about what those tests showed.

[Doug Zielke]

Save the Schnorr washers for the riding lawnmower.
Use safety wire and worry about something else.

[Jim Sims]

The below probably shows what a total nerd I am; I have a subscription to a fastener industry magazine and find it interesting reading. I also use Schnorr lock washer's on my 911 CV joint screws and use other types of Belleville washers many places in my designs. The clamping force of a hardened Belleville or disk washer is very high.

Schnorr serrated washer testing:

http://www.iecltd.co.uk/bearing/products/schwash/images/wirksame_sicherung_deen_072.pdf

Cheers and tight CV joint screws to you all! Jim

[Randy Webb]

Some definitions for various readers:
axial load -- you probably mean the forces at the screw threads themselves; and were comparing that to the much lower force under the bolt head (or under the washer) itself.

Here's something to think about, sports fans: If you drill the bolt head for a safety wire, how much is the strength reduction in the head?

[island911]

next to nil.

[RickKlem]

Okay then

Whats the proper torque rating for this bolt?

Rick

[Decolliber]

Originally posted by RickKlem
Okay then

Whats the proper torque rating for this bolt?

Rick

According to Bentley, 30 ft lbs for the M8 (pre-1985) and 60 ft lbs for the M10 (1985 and later).
If those C shaped plates are not washers, what is their function?

[Decolliber]

Pelican has the M10 bolts for the CV:

Your search returned 1 matches.
OEM Part Number 900 067 123 01
Price New
Bolt 10x50mm, 24 req, 928 (1978-mid 85), 12 req, 928 (1985-On)
J-067-123-01 90006712301 $1.00

[350HP930]

While my CV joints have been taken out several times I have yet to have a single fastener come loose thanks to proper torquing.

If one is really paranoid about them coming out I would just recommend a little thread locking compound as an easier solution than saftey wire or additional washers.

[Doug Zielke]

Originally posted by Randy Webb
If you drill the bolt head for a safety wire, how much is the strength reduction in the head?

Thousands and thousands of car and m/c racers can't be doing something wrong. Not to mention aircraft.

[Randy Webb]

"thousands..."

Well you misunderstand something -- they are usually using a bolt with a hole made when the bolt is made. Drilling weakens the metal -- by how much, I don't know -- but that's my point.

re: threadlocker -- this changes the torque to bolt stretch characteristics; not likely to be a problem, but who knows?

[Doug Zielke]

Originally posted by Randy Webb

.....they are usually using a bolt with a hole made when the bolt is made.

Yeah?
And tell me where such bolts are available then, in Metric and SAE.

[island911]

Holes in the head . . sheesh, what's the big stress.







Tension loaded.

Any questions?

[911pcars]

Many AN. NAS and MS-spec bolts have drilled heads. They can be found where racers should be purchasing fasteners; at aircraft supply houses.

Unfortunately, AN, NAS and MS only supplies fasteners in SAE fractional inch sizes. Because our aerospace industry uses only SAE size threads, you might have to find the nearest MIG jet supply depot for the equivalent metric parts. For non-domestics, it's a little more difficult to find high-quality fasteners, but Carroll Smith, author of many race-prep manuals, recommends German, Italian and Japanese pieces and discourages using fasteners from Taiwan and Korea.

In regards to the purpose of a flat washer, Carrol Smith notes:

"Flat washers serve as bearing surfaces to prevent bolt heads and nuts from digging into the work surface. They also allow more accurate installation torque or strain measurements."

In regards to socket head bolts and washers:

"The socket-headed cap screw has two advantages over the standard hexagon-headed bolt: First, the head takes up less space, and second, high-quality socket-head cap screws are more readily available than are high-quality hex bolts.

But there is no free lunch and, for many of us, particularly for the racer, they also have three disadvantages: First, they have very small heads. If they are to be loaded in tension, the limited bearing area under the head will prevent tightening the bolt sufficiently to take full advantage of the strength of the alloy - unless, of course, a hardened washer is inserted under the bolt head. Note: The curved plates under the CV bolt heads act like a washer.

"Second, they are manufactured with very long threads. It they are to be used in shear (loading in bending), the excess thread must be removed before thay can be properly installed. And third, the heads are case hardened and are therefore difficult to drill for safety wire."

If anyone wants to clamp highly stressed vibrating and rotating parts together without a washer under the bolt or nut, go ahead as long as you know what you're doing. For the rest of us, I suggest using them.

Island,
I see no weak-colored areas around the drilled safety wire holes either.

Sorry for the longish message,
Sherwood

[island911]

Originally posted by 911pcars
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If anyone wants to clamp highly stressed vibrating and rotating parts together without a washer under the bolt or nut, go ahead as long as you know what you're doing. For the rest of us, I suggest using them.

Island,
I see no weak-colored areas around the drilled safety wire holes either.

Sorry for the longish message,
Sherwood

Sherwood, yeah, thats what I expected to see, and show.

I imagine the holes could cause a weakness, around the socket, when torquing one down, if the hole were HUGE. (the hoop-stresses maybe slightly higher . . .I didn't feel like doing that analysis too.)

On the use of extra washers, we differ. You're saying (to paraphrase) "if you DON"T know what your doing, use an extra washer."

I'm saying if you DON"T know what your doing, then you're better off leaving it alone. . . ..trust the Porsche engineers.

As has been pointed out, those 'half-moon' plates distribute the load. I will also add, that (unlike a washer) those 'half-moon' plates can't spin . . .they are constrained be the next bolt over.

I think the best advice, for the guy installing CV's is; reallize these things can be easly installed poorly.