Nylock self locking nuts on main bearing bolts?

katy

katy

Well-known member
Anyone ever use these? Pros? Cons? Maybe a different style of self locking nut?
Working on the rear main right now and thinking about using self locking nuts as it would save the aggravation of trying to line up and insert the cotter pins.
 
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They are all I ever use but once only for each nut. I use an old one for first assembly, then go around and put new ones on once everything is right.
 
Take one measure how much torque it takes to turn on a bolt,add that to the torque value.There is also different grades and quality of nylon used in the nuts.I foung phosphate treated grade 8 tall nuts and loctite for my mains,used dark nylon grade 5 for the rods
 
Use standard nut and a split lock washer. Firs put a little bit of silicone around the bolt where the lock washer will sit.
 
Pretty sure that nylocks loose a lot of their locking ability at the temperature an engine runs at. There are all metal lock nuts that are rated for use at higher temperature. Split lock washers on main bolts are just sloppy practice.
 
I don't use any kind of locking nut, just grade 8 nuts, w/longer threads if you can find them. The last couple of engines I did, I machined Model A lug nuts flat, and installed them. They are of good quality, have long threads, and look cool.
 
GPierce said:
Nylon lock nuts are not allowed in the engine compartment of an airplane in most circumstances.
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That was my first thought when I first read this thread. If you don't mind me asking, why would you even want to go to this? What is the advantage, ...especially on connecting rods that if you damage a thread with a lock-nut, the rod is ruined.
 
I am 75 years old and for years, I was a journeyman machinist and assemblyman for Skagit Corporation in their transmission department building heavy equipment. We had many government contracts and we had to follow strict government rules of assembly. Anything inside of enclosed cases, etc, had to be safety wired. Even cotter pins were not allowed. To think that one would even depend on a lock washer or a nylock nut to keep the internals together is scary, it would not be allowed by Skagit Corporation. Cotter pins are still the most reliable for the model A Fords internal fasteners. Next thing we will be reading is that the nylock nuts canl be used instead of cotter pins to keep your front spindle nuts in place. Scary practice....
 
Dan McEachern said:
Pretty sure that nylocks loose a lot of their locking ability at the temperature an engine runs at. There are all metal lock nuts that are rated for use at higher temperature. Split lock washers on main bolts are just sloppy practice.
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Dan I'm not advocating using lock washers on connecting rods.
Using a split lock washer on main bolts is done and has been done by quite a few engine builders with good results.

I don't think the original poster was asking about using the nylon lock washers on connecting rods but only on the bolts for the mains.
 
I saw a study years ago that showed that nuts will come loose EASIER with a split lock washer than without. They simply don't work. I only use them as spacers or to add a little friction for a bolt that I don't want tight but don't want floppy loose either. If a lock washer is to be considered, a "nord-lock" is the only one i would ever consider for such an application. Nylocks are good for some applications but not all. Stover locknuts are great but there is no way to get a proper torque reading so are useless for any application that requires a specific torque rating. Nord-locks are awesome but if i was to use them for main/rod caps, I would still use a cotter pin because the provisions are there. https://www.nord-lock.com/insights/videos/how-does-the-nord-lock-washer-work/
 
If ARP makes a nut that fits and is appropriate for engine internals, I'd use them. Marsden nuts are likely strong enough as long as they are a good grade that would be appropriate. Ford hardware seemed to always be appropriate for the task even if it is antiquated.

Aircraft engines generally use very high grade hardware for the con rods. They are stretch torqued on the higher performance engines and have no locking feature but then at the torque level they are on, they don't need a locking feature. They are even copper plated for corrosion resistance on the Lycoming engines. The engine case forms the main bearings and they use very large through bolts with very hard nuts for torque up.
 
I have used this type of locknut on my rods. Got them from McDonald Douglas aircraft salvage store. They are all metal and worked well.
 

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Welcome to modern polymer lock nuts..high temp,oil resistant with a positive lock under torque.Amazing the things you learn when you adapt to the times..yes,you can still buy cheap nylock nuts,white nylon grade two nuts..but there are better choices.We are talking about a 35 foot pound assembly in an environment well under 300 degrees...modern high temp mil spec nylock nuts far exceed those requirements.

https://www.extreme-bolt.com/a-286-lock-nuts.html


I wouldnt use an all metal distorted lock nut..it relies on galling the thread to lock the nut.Anerobic sealant,(loctite) nylock nuts or even distorted lock nuts are better at holding positive torque than a cotter pin.Cotter pins are usless in that application,other than keeping the assembly from completely coming apart..the actual process of pinning the nut tells you you are not 'loading' the assembly to retain a torque value.
 
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Torque values on fasteners is used to pull all the potential stretch out of the assembly,which is why torqued assemblies usually don't use any type of mechanical or chemical locking device..In this case,the use of locks are essentially double redundant,provided you torque the assembly correctly.
 
MS21042 and MS21043 nuts are used a lot in aviation but they are generally a nut that needs to be replaced when the drag torque becomes too low. They are used a lot on turbine engines in their stainless steel form since most of the screw/bolts are also stainless. They use a lot of small ones closely spaced to hold the turbine and compressor sections together. I don't know if I'd want to use them inside an engine or not. They are pretty strong but they are also pretty thin in cross section.

Those MS20500 nuts in the link on post #15 are a Marsden type that are also silver plated for heat corrosion resistance. There is an MS21045 nut that is the same design but in steel with type II Cad plate. All of the above are tension nuts rated at 125KSI tensile strength. The thin nylock types are made for shear. The don't have a lot of tension strength. The thick nylocks do and are tension types but keep in mind that the nylock material takes up a good bit of room for metal threads.
 
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Nylon locking nuts are generally rated for 250 degree F service, but I question if that is accurate in motor oil. Perhaps the motor oil degrades the nylon. I would not take the risk.
 
I used the Snyders set of grade 8 nuts, bolts and sealed washers for mains and the ARP nuts recommended by Jim on the rods.
 
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Main bearing nuts, $2.35 a pound at the industrial salvage place.Metric hard washers opened to slip fit with a die grinder.Dab of triple bond on the block side,blue loctite on the threads.Grip length of rod bearing nuts is important but not overriding,the hydrodynamic principle protects the rod bearing assembly,it removes shock load and heat,the fastener is not subjected to undue stress in street applications.

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there is magic in a thin film of oil..
 
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