Studs vs. bolts

[BDA]

I think the nylon really keeps vibrations from loosening the nut rather than acting as resistance to loosening (which could be a distinction without a difference!).

On a similar subject, Carroll Smith does not believe in split lock washers. I don't use them unless I have no other choice. I suspect the spring action is intended to perform a similar function as the nylon but a friend of mine who was an engineering classmate and became a REAL engineer and recently retired from Shell Oil as one of their best rotating equipment men told me an interesting story from early in his career. They had a machine that was literally shaking itself apart. They used regular nuts with spring lock washers and the vibrations were so severe that the ends of the spring washers actually gouged grooves in the metal as it loosened!

So what does that mean? Maybe the way they really work is that the sharp ends of the lock washer dig into the nut and the part - at least in part. If that's true, that means that it's probably not a good idea to put a flat washer under the spring washer because it will just rotate as it loosens defeating what could be part of the purpose of the lock washer.

Incidentally, my buddy figured out and cured what was causing all the vibration and was one of his early successes. I don't remember if he changed the nuts to lock nuts though.

[4129R]

I was taught by a meticulous rally mechanic to lock wire any nuts that could vibrate loose, and when going under a car, take spanners with you to check all the nuts and bolts are tight.

He also argued with the head of Austin-Rover motorsport on the Tour de Course International Rally that no-one should be asked to go under a rally car held up only by a jack, i.e. no axle stand.

On this basis, to drill and split pin a nut which is 6 full turns on the thread, but too short for a Nylock, gets my seal of approval.

[jbcollier]

I agree that lock-wiring is an excellent idea.  I run a Ducati single that vibrates quite a bit.  Everything essential is lock wired.  Lock wiring requires a hole through a single "ear" of the nut.  The strength of the bolt is only compromised a very small amount.

Drilling right through the centre of the nut and using a split pin?  Not so much.  You are weakening both the nut and the stud/bolt.  Split pins are always at the very end of the castellated nut, not in the middle.  You also can't check the nut, or tighten it if things settle.  If you want to use split pins, then use a proper castellated nut as well.

[GavinT]

G’day BDA,

About your hypothetical re the A-arm halves being welded together at the outboard end, that makes sense, too - no mechanical engineer here though.

I was thinking through my reply when I read your phrase, “in unambiguous double shear applications”.
That’s it in a nutshell, for me.

If we were talking about a crane lifting 100 tons, then we’d be perfectly justified in wanting the hook to be attached in double shear. But I agree, our front A-arms aren’t primarily looking to perform that same discreet function.

In fact, if we were to consider function, then the existing A-arm mounting system is reasonable IMHO.
If there were another chassis plate with a through hole on the outside of the A-arm, that would complete the double shear picture.

But is that what we want?
I say, no.
If we hit a curb, it’s likely either the A-arm or the pin will bend. That’s a much better outcome than the chassis taking the full force. The same argument applies to folk who consider changing fasteners to Grade 8 to be an upgrade.

On the non-reusability of Nyloc nuts, I strongly suspect this recommendation originates from the Nyloc manufacturer and likely relates to liability issues.
The Nyloc OEM has no control over the broad range of intended applications and therefor is in no position to sanction a second or third time usage.

The other thing to consider with the half height Nyloc nut is this; if we can’t apply full torque to it, then the assembly can’t function correctly. I somehow doubt clamping the inner steel sleeve of the rubber bush is achievable with 2 - 3 threads.

I’m glad you mentioned Carroll Smith’s books. I think I’ve got the same ones and everyone with a Lotus should have them on the shelf, I reckon . . even if it’s only to figure out exactly how sneaky Colin was. 

[Grumblebuns]

I managed to remove the offending nut to get a slightly more accurate length of the exposed threads. The picture of the measuring scale is washed out by the flash but it measures about 0.5" from the end of the bushing inner sleeve. The removed nut and washer measures 0.663"/16.84mm. At the rear attachment point, the pivot pin appears to e flush with the end of the nut. From Gavin's picture of his nut next to the pivot shaft threads, appears that I'm about three threads short of minimum acceptability for thread reach.

So for me the question is what is safer, having a thinner locknut with fewer threads engaged on the shaft or my current situation, a wider nut with maximum threads engaged but can be safety wired to prevent loosening assuming same material grade. Right now I'm leaning towards safety wiring the nut as the safest option with wicking blue locktite as backup.

I can't figure out where the difference in pivot pin thread length between Gavin's and mine is.   

   

[BDA]

Gavin, I agree that the standard A-arm arrangement is certainly reasonable. Except for the use of trunnions, it's not different from older race car suspensions. As you mentioned, the frame is important to protect (thus the driver and passenger on either side to protect it in the event of an accident!) and that's why the A-arms are designed the way they are - so that in the event of an accident, the A-arms will absorb a lot of the energy of the crash. I would think that the pivot pin would survive almost any accident. Of course, now that those arms are becoming scarce, we have to go to tubular replacements which puts the frame at risk.

I always used either Grade 5 bolts or AN bolts because they are less brittle than Grade 8. I've known people who use Grade 8 without problem and I know someone who used a Grade 8 bolt and it broke in an accident. I don't think Grade 8 is the wrong choice but I think Grade 5 or AN are preferable. AN is more preferable because of the reduced length of threads but are a lot more trouble because it requires you to keep a large inventory of lengths and you must measure the thickness of the clamped parts.

Smith's books are excellent. They are invaluable if you're building race cars and while a lot of the information he gives out is pretty esoteric with regard to street cars, it's always nice to understand things at a different level.

Re: "unambiguous double shear" - I'll be asking my REAL engineer friend what he thinks about parameters for double/single shear.

[BDA]

Joji, It seems to me that when I took my car apart, it had full height nuts on the pivot pins and everything fit but for some reason, when I put my car together, I needed half height nuts. I offer no explanation, nor do I trust my memory, but I don't think there were half height nuts anywhere on the car originally.

There should be a two or three threads past the nut when it's tightened but if all the nylon grips the threads, that should be sufficient. I put a big washer on the outside of the A-arm half (under the nut) to help retain the A-arm in the unlikely event that the bushing delaminates. That's probably overkill but maybe that's why my pivot shafts seem shorter.

It maybe time for jet nuts.

[GavinT]

I can't figure out where the difference in pivot pin thread length between Gavin's and mine is.

G’day Joji,

Did you measure the inner steel sleeve of the rubber bush?
My current thinking is that it’s a bit too long.

My bush inner steel sleeve: 35.05 mm (± 0.02)

I wouldn't consider using a half height Nylock for this situation, because I doubt you could apply the required torque loading.
Safety wiring and Loktite would be a PIA in my book.

According to the Pegasus Racing site, a 1/2” Jetnut is 0.410" high . . and at $4.99 each, sounds like a quick and easy remedy.

https://www.pegasusautoracing.com/productselection.asp?Product=MS21042


BDA,
Since you also experienced the need for shorter nuts, I wonder if you’d also replaced the A-arm bushes at the time of rebuild?
If yes, perhaps there’s some replacements out there that are a little longer than the OEM items and that’s also what Joji is dealing with?

[EuropaTC]

perhaps there’s some replacements out there that are a little longer than the OEM items and that’s also what Joji is dealing with ?

When I fitted poly bushes the stainless inserts were fractionally longer than the OEM ones and stuck out too much IMO. From hazy memory I think I ground them down a touch so they were only just proud of the bush. When I fitted new wishbones to the Elan later on I bought conventional bushes from SJS and they were correct.

It wouldn't surprise me at all to find replacement bushes not quite to the same dimensions. But realistically we shouldn't have to worry about one or two mm on this sort of thing, I'd be tempted to replace the pin for a longer one instead.

[BDA]

BDA,
Since you also experienced the need for shorter nuts, I wonder if you’d also replaced the A-arm bushes at the time of rebuild?
If yes, perhaps there’s some replacements out there that are a little longer than the OEM items and that’s also what Joji is dealing with?

I did replace my bushes but they didn't seem unusually long to me. I would say with all this talk about it, I should take a wheel off and make sure I'm being accurate.

[Grumblebuns]

G’day Joji,

Did you measure the inner steel sleeve of the rubber bush?
My current thinking is that it’s a bit too long.

My bush inner steel sleeve: 35.05 mm (± 0.02)


BDA,
Since you also experienced the need for shorter nuts, I wonder if you’d also replaced the A-arm bushes at the time of rebuild?
If yes, perhaps there’s some replacements out there that are a little longer than the OEM items and that’s also what Joji is dealing with?

I can't really measure the inner sleeve without removing the A arm. The Europa manual doesn't even address the bushings so no specs or how they should be pressed in. The parts manual for the S2 shows a washer only on the outside ends of the bush, no washer on the inside, mine has a washer on the front inside bush. Looking at the picture of my bush area, there is only about 1/8" protruding from the A arm sleeve, zero from the rear due to the washer I mentioned earlier.

With the thickness spec Gavin mentioned for the jetnut, I'm leaning towards going that route, its simpler than drilling a nut for safety wire.   

[GavinT]

I'd be tempted to replace the pin for a longer one instead.

I recall this was discussed some time ago but I don't remember the outcome.
My foggy memory says that the TC lower pin is removable but the S2 pin isn't. 

[cwtech]

A very interesting discussion about locking nuts.

As shown, not all applications can use nylocks, or sometimes locking nuts are just not at hand.

For many years, we made our own lock nuts using a common hex nut and never experienced premature loosening.

(1) A common hex nut of the appropriate thread size is placed on a hard, immovable surface.

(2) The rounded end of a ballpein hammer (larger than the i.d. of the nut) is placed on top of the nut.

(3) The other end of the ballpein hammer is struck by a larger, heavier hammer, thus deforming the top few threads of the nut.  (Yes, I am aware of the risks of striking a hammer with another hammer, so common sense needs to prevail.)

(4) The deformed threads are the "outer" portion of the nut and are the last to contact the male threads.   ....The amount of deformation needed can be gauged by the force needed to thread the nut onto male threads.

(5) The nut can be re-used if deformation is re-done, but why bother?  ...It's a common hex nut!

[Gary t]

It is fun to watch the metamorphosis of a topic.
From my part box new Dave Bean bush (old style)inner length 1.365 on my dial caliper.
Gary

[BDA]

The parts manual for the S2 shows a washer only on the outside ends of the bush, no washer on the inside, mine has a washer on the front inside bush...

With the thickness spec Gavin mentioned for the jetnut, I'm leaning towards going that route, its simpler than drilling a nut for safety wire.

I also put a washer between the frame and the A-arm bush in addition to one on the outside because I experienced delamination in one or two bushings that I recently said was unlikely (I think I've already apologized for my geezer memory). Perhaps that's why yours also has one.

I agree with your not wanting to safety wire the nut. It's a bigger job than it looks as you need to get a jig for drilling the hole in the nut for the wire. I had one once and it was pretty hit or miss so I take that to mean that I needed to spend more money on one.