Nyloc Big End nuts

[Parazine]

I finally managed to collect my crankshaft and flywheel assembly for the Top Hat engine from the balancing shop yesterday. I was chatting with the guy there who builds a lot of competition engines. I explained at one point that I was intending to use Nyloc nuts on the big ends, as I have done for the last twenty years or so. 
He scratched his head and said "I'm not sure I would use them. They're good up to about 70 degrees centigrade, then they lose their grip. I'd stick with the split pins and castle nuts."

I know this has been discussed before but what do the rest of you guys think? I've never had a problem with Nyloc nuts but...…..

[Steve Jones]

Have used Nylocs on Austin rods for many years. Never had any issues. However, never re-use. Always use new.

Steve

[Colin Wilks]

According to Wikipedia nyloc nuts retain their locking ability up to 121° C

[Alan]

I’ve always used nylocs with Austin rods. No problem.

[Nick Turley]

I have had a similar conversation suggesting doubt with a good engineer.
This worried me at the time. 
Having said that nylocs are what I use, never ever had an issue with them.
Like Steve says, only tighten to torque once, after use throw away.
Have total confidence.

[AustinWood]

I use Nyloc nuts. However all metal Aerotight nuts are available which can I believe be re-used.

[Alan]

A year or two ago I rebuilt an engine which had clearly never been apart before. The split pins were still a sliding fit in the big end bolts. In 85+years the nuts hadn’t shifted at all. It reminds me that an Engineer for whom I have greatest respect once told me that correctly designed fasteners didn’t come loose. He would ever allow the use of any thread locking device on the grounds that they were unnecessary. That was over 40 years ago. My experience has been that he was right.

[Ivor Hawkins]

Every Seven engine I have built I’ve used castle nuts and split pins, however....

Every other engine I’ve built, including perhaps a dozen racing engines I’ve always used Nyloks without a problem!

I would go with castle nuts out of tradition, but would have no qualms using Nyloks.

[Robert Leigh]

I use Nyloc nuts and Loctite and have not had any problems with this system. Almost invariably I have found the old bolts with split pin provision have been stretched by overtightening to get the split pin to line up.

[John Mason]

I also use Nylock nuts without problems and torque down. It is straight forward to get the correct tightness with nylock as there is no split pin hole to line up with. With s/pins you have got to file the nut thinner to get the correct tightness and get the pin hole correct. I am no engineer but if the nut is tightened correctly i.e. correct torque should it stay tight whether it be nylock or castle nuts and pins. I use nylock because it makes the job easier. I have no problems in 20 years but do not have a competition car.

An old mechanic who worked in the 30s 40s and 50s always told me tight is tight however things didn’t work to such fine tolerances then and I bet there were no such thing as stretch bolts.

John Mason