Washers under Big End Nuts

[Jamie]

Daft question, no doubt, but do people use plain, spring or no washers under the big end nuts? Instinct tells me to use plain washers, but I am not sure.

Jamie.

[Robert Leigh]

Bigend nuts should not need washers. Originally they were split pinned and the nuts are sized for the castellations to be correctly positioned for the split pin. I have found stretched bolts where washers have been added to create the correct location for the split pin, but this has been the result of the bigend bolt being stretched by overtightening. Such bigend bolts should be scrapped. Many of us (most?) now use self locking nuts which avoid the problem of the split pin not lining up with the castellations. The bolts locate in the top half of the bigend so neither the bolt nor the nut can turn, obviating the need for any washer.

[Ruairidh Dunford]

Some of the nylocks sold for this application are not quite tall enough to get a socket on and will need a washer to lift them up slightly.

I have always used good quality spring washers for this - no doubt this is incorrect but continues to work, without any issue, for me over a thirty year period in hundreds of engines.

[Jamie]

Thank you.

[bystander]

Washers found under big end nuts may also be a sign that the caps have been filed in the past to take up wear - a common bodge in days of yore.

[Bob Culver]

Ordinary spring washers come in two forms; with and without a burred end. Tha latter seriously alter torque and the bolt is loaded  eccentrically. I doubt if the other type contribute much. If the cap faces abut soundly, threads do not run out, not soft low grade nuts, no dirt, heads seat securely, no lock required. Very many old bolts are waisted , presumably due lazy mechanics tightening to the next slot. Adjusting the faces can be tedious and all have to be kept in order..

[JonE]

I've just bought some Philidas locknuts - apparently they can be re-tightened 6 times - as someone had mentioned that some nylocs weren't up to same standard they used to be decades ago. So worth making sure you are getting nylocs from somewhere reputable like a 7 supplier. Be interested to know whether any bad points about Philidas?

[Colin Reed]

HI Jon,
IN The aircraft industry it is not recommended to (reuse) any type of self locking nut on any thing that rotates or is subject to vibration.
They are not expensive, so why bother it could end up being expensive

Colin 
NZ

[Rogerfrench]

Washers can be used to balance a light big end.