Big end nuts

[Howard Wright]

Hi All

Surprised I haven’t been censored for the thread title  .

I’m amassing bits for my engine build and will be ordering big end bolts and nuts shortly.  I was going to use Nylocks as I have with the two engines I have built previously but I came upon a thread on the old forum questioning the use of Nylocks in hot engines.

So I’ve been investigating other nuts namely Aerotight, Binx and Philidas.

Anyone use these and if so any comments!

Cheers

Howard

[Ruairidh Dunford]

I have used nylocks, exclusively, for the last 25 years or so - they work perfectly in my experience.

[Chris KC]

The thing which really keeps the joint done up is tightening it to the point which generates just the right amount of tension in the bolt. In modern industry this is established by extensive bench tests and the parts are highly consistent, enabling precise setting torques to be established. Self-locking nuts use some of that torque - worse still a variable amount - to enable their locking features, and interfere with the torque vs clamp force relationship, making the joint less reliable.

Vintage builders don't have bench test labs at their disposal and in any case no two cars or components are the same, so the right tightness is far more a matter of individual judgement, and a 'safety net' in the form of a locking feature has something to be said for it. But the less - and more consistently - that locking feature interferes with the torque vs clamp force relationship the better. On that basis I'm with Ruairidh, Nylocs every time. I wouldn't use the other types in this application.

[Colin Reed]

If using Nylocs make sure they are HT Grade 8 (NOT) Standard as they are Grade 5

Cheers
Colin 
NZ

[Stuart Giles]

Nylocs working range is up to about 120C IIRC. Use some Loctite Nutlock as well if you want some extra confidence; that has a working temperature that goes up to 150ish C. As Ruairidh says, there must be hundreds if not thousands of motors built with Nyloc nuts retaining big end caps which are still running without issues.

Finding Binx, Philedas, Aerotight, Dotloc or Stenor all metal locknuts in BSF sizes now is likely to be a mission, as they are pretty well certain to be old stock that's been sitting on a shelf somewhere for several decades.

[Colin Wilks]

I shall use M8 HT bolts with nyloc nuts in my sports engine rebuild. They fit the original Austin rods perfectly with just a touch of emery on the shanks.

[Zetomagneto]

If going metric I would probably use K nuts, they are all metal self locking.
I am not a fan of Nylocs in a hot environment , I do wonder if they haven’t come undone because they were done up tight, rather it having anything to do with the nylon part
You could go to UNF and probably find all metal locknuts for UNF

[Alan]

I’ve always used nylocs on big end bolts. Not because they are needed but because customers expect them. I’m reminded of a well respected colleague who would never use any kind of self locking device- he said rightly, that correctly designed fasteners don’t come loose. I have a feeling that if a nut was going to come loose, being a nyloc wouldn’t stop it.

[Chris KC]

I agree with your colleague Alan, but I venture he may have meant 'correctly designed joints don't come undone'.

Correctly tightened, proper quality nuts and bolts only come undone if there is slip between the joint faces, or compression of the joint - both of which point to a basic design flaw in the joint itself.

And yes, an axial hammering at 100 cycles per second can remove any nut, self-locking or otherwise, in a jiffy - just like an impact driver.

[Howard Wright]

Hi All

Thanks for the input.

I’m homing in on using 8mm bolts with Grade 8 Nylocs.

Good warning Colin.  I contacted a couple of suppliers regarding their BSF Nyloc nuts and they only stocked Grade 5.

Cheers

Howard