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MG TD TF 1500 - Torquening castellated nuts


As far as I know, torquening the original castellated nuts in main bearing caps and rod caps implies to set them at the required torque and then going to the next hole for the safety split pin.

Does this means to tighten more or to loosen the nut?

In some cases, I need to rotate the nut practically 1/6 of a turn (60 deg) and that seems to produce to much a variation in the specified torque.

J. Benajes


You must not over tighten. Even more importantly you must NEVER slacken the nut. Many people recommend taking a skim off the base of the nut so the castelations line up at the correct torque. Problem is you really need a threaded mandrel in a centre lathe to ensure the face of the nut is square to the thread. If it isn't you run the risk of the nut tilting on the bolt and damaging the thread. A better way is the file the appropriate castelation with a thin file so the split pin is an easy fit. Even easier is to use nylock nuts.


Jan T
Jan Targosz


One thing that might work is swapping the nut with another if you have two that don't line up. (I used nyloc type.)

Good luck,
Evan Ford - TD 27621

A thin washer can also do the job on a castellated nut. You can even calculate the shim thickness by knowing the number of threads per inch, calculating the distance per revolution of the nut, and then taking 1/12 of that distance as your washer thickness to get you to the point of being halfway between holes, to being dead on.

You can also pick a washer that is one revolution plus whatever distance you need to make up to get to the hole.

D. A. Braun

Thank you all for your useful suggestions.

The easiest way seems to go for nyloc nuts, which must be very easy to find here in continental Europe. Are they reliable? Must I look for some specific feature of the nut? Or, will do the job every high-grade 12-1.5 mm nut?


J. Benajes


If you check the workshop manual, on page 7 it gives the torque values, then on the following line it says (to next split pin hole) to me, this implies than you can tighten the nut to line up the slot and hole. This is how I did mine.

John Scragg

John Scragg


Bad news - I don't think it will be all that easy to get nylocks unless you go to a mg specialist. The nuts whilst being metric are not standard. I think this issue has been covered before.

Jan T
Jan Targosz

I think a far better solution to filing the nut, is to lap it on a sheet of flat glass with some fine grinding paste. Slow job but more accurate. This could also be done on a washer or spacer instead. Filing a castellation may work if it is coming up to a split pin hole, but not past it. Nylocs are just one modern type of locking nut. There are others that do not rely on a nylon insert to lock. Need to search around a good engineering supplier, perhaps suppling to the aircraft industry. Recently I was looking at a restored aircraft engine, where all the nuts had been wired. Most good engine manufacturers recommend that the split pin lies in line with the crankshaft.This way there is less chance of it working loose.

Hi Jesus, you can loctite the nuts instead of using nyloc nuts. Different grades of loctite are available and if used correctly will give the desired result.

I don't believe that using washers for this application is a great idea as washers are usually made from mild steel or similar. They could flatten out and the tension on the nuts would then alter.


Paul van Gool

I'm not in favour of Nylock nuts. For my current rebuild, I was sent a set of Nylock rod bearing cap nuts. I don't think Nylon was designed for operating at 200C and above, and I believe there's a risk of the Nylon softening and stretching and relaxing its tensile grip on the bolt.

On a small diameter bolt, there's a greater chance for alignment for the cotter pin or wire, than there is on a larger nut/bolt, so I reverted to castellated nuts and cotter pins. The only down-side is the weight of the cotter pin, but at XPAG revs, it ain't like a F1 Ferrari revolvong at 19,000 RPM!

Gord Clark
Rockburn, Qu.
Gordon A. Clark

seems to be a bit of over thinking or reengineering. as john said...follow the factory workshop manual.
tm peterson

Gordon has it right. Never rely on nylock nuts in applications that exceed the temperature the human hand can tolerate without injury. I have seen military hardware tested at high temperature (above 100C) come apart under vibration. The nylon gets greasy.
Also, looking into some WWII aircraft engine rebuild manuals I note rod caps being safety wired. There is an exact method and technique required for near absolute relaibility.

Jim Haskins
1953 MG TD
J. M. Haskins

This thread was discussed between 27/04/2005 and 29/04/2005

MG TD TF 1500 index

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