What type of nut to use on exhaust manifold studs?

[mangocrazy]

I'm trying to decide on which type of self-locking nut to use on the exhaust studs (head to manifold connection). I realise that Nyloc nuts aren't suitable due to elevated temperatures melting the nylon insert, but there seems to be a wide variety of all-metal locking nuts to choose from. I was browsing the website of DS Fasteners Ltd ( https://www.dsfasteners.co.uk/ ) and they seem to stock most of the available varieties. Does any one type have any clear advantage over the others?

[rossocorsa]

I just went with what GC supplied I can't even recall if they are locking nuts or not TBH but I'm thinking not, must check when I'm in the garage

[HFStuart]

Silver plated K-nuts work best for me. Brass or copper ones never seem quite strong enough and 'aero' nuts lose their self locking properties with the heat.

https://www.demon-tweeks.com/uk/demon-tweeks-metric-hi-temp-aerospace-locknut-k-nut-243561/

[peteracs]

Hi

Those look very similar to the nuts I used on the Saab manifold which are down as one time use, which I guess is as a result of the deformed thread giving the locking action.

Peter

[mangocrazy]

The K-Nuts certainly look very suitable for the job. The ones I was looking at from the DS Fasteners catalogue are these, supposedly suitable for high or low temperature use:

https://www.dsfasteners.co.uk/turret-self-locking-nuts

No idea how they compare on price though. I've emailed DS Fasteners asking what their recommendation would be for this application. I'll post their reply up as and when it arrives.

[rossocorsa]

I had a quick look at my engine and I think they are just plain nuts, they will be whatever GC supplied me with as he made up a full set of fasteners for me.

[mangocrazy]

The reason I ask is that I can remember well how loosening exhaust nuts was a regular thing in the earlier days of my Beta ownership. I also remember what a PITA it was to get to the nuts to replace or (if I was lucky) tighten them up again. This was with the OE cast iron exhaust manifold. Once I'd swapped to the CSC 4-2-1 exhaust with steel flange it did seem to become much less of a problem, as I recall. Perhaps something to do with differential expansion/contraction of cast iron/steel/aluminium, allied to vibration and torque stresses?

As I've now got two hot and hard to get at interfaces to manage, I thought I'd better start thinking about preventative strategies. Having said that, the strategy I'm currently using by default (leaving it sitting immoblie in the garage) is working the best of all...

[WestonE]

I use flange nuts that look like the K nuts but have a serrated face on the flange. They are zinc plated and stay in place. I do not trust brass or copper at he manifold on our engines.

Eric