Nylock nuts on big end bolts

[panda911]

Hi.
I have read some discussion on the use of nylock nuts on Mk1 Minis and think that a bit of common sense for me, takes precedence over originality. Is there a downside in using them on big end bolts.
Thank you
P

[Peter Laidler]

Thinking on my feet...., on a subject as important as and with the loadings imparted on these nuts, it's an important matter, I'd suggest that you stick to the correct spec nuts and torque figures.

That's just the sound engineering principles in me speaking out aloud.

I hope others will come one board the discussion, either way.......

[Exminiman]

Personally, I would not use Nylocks in a situation (heat, oil, spinning forces) like a big end - why would you, what’s the benefit ?

Do you know what temperature the nylon starts to soften and lose its grip ? Quick google shows apx 120 degree C, which might be okish but then what spec is your nut made to…..and what’s the point if the nylon if it degrades with heat…

Does the Nylock degrade if immersed in oil ?

Also the inertia of the nut spinning on the big end….I suppose you torque it down, but then what’s the nylon for?

Could you even buy Nylocks to the required spec?

[MiNiKiN]

The securing effect of the nylon inserts is virtually nonexistent. So whats the point of using them? Provided the correct torque is applied to standard nuts in the right way, there is nil benefit, just added risk.

[InnoCooperExport]

Yeah I can't imagine it's a good idea or even why you'd want it. I am unaware of big end bolts coming loose is a problem that needs solving either. I'm with Peter and Exminiman. Not to mention I recall a whole discussion about torquing Nylocks and it being an unreliable measure because of the nylon. So beyond it not being a good idea I'd say it's a bad idea.

[Fanfaniracing]

Same for me.

In my Engines i use ARP Bolts and Nuts whenever i can...

[BAD942B]

I used HT nylock nuts on the big ends on new rod bolts on my S in 1981, no loctite either, I suspect they came as a kit from Minispares.
When I stripped the engine earlier this year they were still tight, perfectly serviceable after 21000+ extremely hard miles, including several hillclimbs &b sprints inc Goodwood, 7k in every gear & occasionally in top (once on the dual carriageway near Coleshill nick 4 up) but 100mph most every time I used the car once fully warmed, 84 bhp at the wheels.
It was my 1st really fast car, ate Golf GTIs, Astra SRIs & most everything else I came accross.
The engine cried enough due to piston failure that started at Goodwwod in 1985, not due to oil pressure issues or anything else issues, the 2 piece damper kept coming loose so was replaced by a 1275GT one.

[Peter Laidler]

This is one of those great questions....... If I was still in teaching mode, it'd be a great question to set a group of eager and keen would-be tech/engineering students.

The irony is that we used high tensile spec nylocks in the cannon mountings and turrets without problems. Mind you, the whole thing shuddered and shook like a kango hammer

[BAD942B]

The real answer is as with any fastener is the correct tightening torque in the 1st place, a poorly tightened or loose fastener will just come straight undone

[robanzac]

It may help to think of a fastener as tension spring (because it is, one with a very high spring constant)
Torquing a fastener is all about creating pre-load in the fastener that is higher than any load that the fastener will be subjected too.
Or to put it another way, creating a clamping force that is higher than any load force trying to spread the clamp.
If you achieve this then there will be no bouncy bouncy in the fastener, all clamp faces will remain seated (which includes the faces of nuts, washers, whatever etc) and hence no opportunity to come undone.
If your pre-load is too low and there are frequent enough fluctuating loads (e.g vibration, thermal, force pulses), there will be bouncy bouncy in the fastener and it will eventually come loose. This is where spring washers, lock washers, nyloc nuts, loctite can help.

[MiNiKiN]

If your pre-load is too low and there are frequent enough fluctuating loads (e.g vibration, thermal, force pulses), there will be bouncy bouncy in the fastener and it will eventually come loose. This is where spring washers, lock washers, nyloc nuts, loctite can help.

Well explained, though I have a caveat.
If your pre-load is too low:

• spring washers and lock washers (except NordLock) help in following way: they do Fuck all!
• nyloc nuts, loctite: prevent the nut/bolt getting completelly lost. But your bolted connection is fu*ked nevertheless because of pre-load loss.

I accept many still believe in spring washers and nylocs and so on. But the only reason why they seem to prevent loosening of the bolt is the correct tightening torque / pre-load applied to the fastener. So from my experience in railway (bogie) application, where you knowingly have loads of vibration, the only solutions mostly lasting are conical spring washers and Nord-Lock. Both of course require precisely calculated pre-load requirements and meticulously adherence to the assembly instructions.

[BAD942B]

If your pre-load is too low and there are frequent enough fluctuating loads (e.g vibration, thermal, force pulses), there will be bouncy bouncy in the fastener and it will eventually come loose. This is where spring washers, lock washers, nyloc nuts, loctite can help.

Well explained, though I have a caveat.
If your pre-load is too low:

• spring washers and lock washers (except NordLock) help in following way: they do Fuck all!
• nyloc nuts, loctite: prevent the nut/bolt getting completelly lost. But your bolted connection is fu*ked nevertheless because of pre-load loss.

I accept many still believe in spring washers and nylocs and so on. But the only reason why they seem to prevent loosening of the bolt is the correct tightening torque / pre-load applied to the fastener. So from my experience in railway (bogie) application, where you knowingly have loads of vibration, the only solutions mostly lasting are conical spring washers and Nord-Lock. Both of course require precisely calculated pre-load requirements and meticulously adherence to the assembly instructions.

lock washers are a disaster, made of mild steel they can deform in service & leave the fastener loose, better not to use them & tighten the fastener properly, even use loctite, the bodgers friend if not used properly

[BAD942B]

always use a flat washer where possible to spread the load, not the thin variety either.
on a connecting rod there often isn't a need due to the nut tightening down onto a correctly machined surface

[251 ENG]

All cooper s rods were fitted with nylon nuts as original.

Personally wouldn't use anything but ARP fasteners, assembled with correct ARP lube , torque correctly and then resized

[winabbey]

All cooper s rods were fitted with nylon nuts as original.

AEG147 is the nut for the big end bolts.

https://www.minispares.com/product/Classic/AEG147.aspx

You'll see in the comments for the above listing the following warning.

Replacement for the original 'S' big end nut, this looks the same but is an up to date modern nut that grips on the thread replacing the plastic nyloc type. The original plastic insert type, when under stress from very hot engines became liable to disintegrate. Alternative nut EAC5541A is a multipoint nut from the later series of nuts with a clamping shoulder base.

[Exminiman]

Originally, in some engines, they used to specify soft lock tabs on mains caps, something no one would re-fit now.

[r.tec]

My professor at university giving Construction Elements in automotive engineering always said, not to use anything else than a bolt and nut. If the torqued nut and bolt are in the right region under any load the bolt must be under tension. Then the nut has no chance of loosening itself. You must consider a bolt as a spring that is in constant tension.
It is a bit tricky to calculate the "right" tension i.e. torque, so I rely on the BMC, Leyland and whatever they were called at the time and the ARP-guys that they did the right calculations for the job.

[Peter Laidler]

R-Tec is dead right in engineering terms. With a nut torqued-up, the bolt is simply a round spring under tension, that's pulling the nut down hard. The biggest killer is vibration

Also taught to us AFTER our apprenticeships and Uni, by the experienced old-hands on the bench, is that contrary to the pages and pages of info in 'Machinerys Handbook *' manual locking mechanisms are easy to learn. Because after the first failure, you don't make the mistake again

* Machinery's, the engineers reference bible .

[rnp68]

1592 pages of useful engineering stuff

[Peter Laidler]

Yep, the engineers Bible........ Or as we used to all it, the grown ups Zeuss booklet!