Rod and Main Nuts

D

DBSHELTON

Senior Member
I really don't like messing with cotter pins and castellated nuts on an engine. Anyone replace their Con Rod Nuts and Main Bolt Nuts with 12-pt ARP Nuts? I know the stock setup has worked for 90 years, but this seems like a better way.
 
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I use tall phosphate coated grade 8 main nuts with loctite..found them at a hardware surplus shop..I get a ration of crap on here for using high heat nylock nuts on my rods,you can get them that stand a working temp of 350 degree,your engine oil temp shouldn't exceed 220 or so. they work,and hold..high heat has colored nylon,either red or blue,not the white..
 
I used self locking nuts on the rear main recently, it hasn't been long enough to evaluate how good they perform.
 

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ARP #300-8333 is a 10-pack of 12 point rod nuts. Another advantage of them is when an A pan is used on a B block, the pan needent be dimpled. On the last few engines I built, I machined wheel lug nuts flat (removed the taper) and used them as main nuts. I re-spot face the rear cap, use hardened steel flat washers, no wire, loctite, just oil and torque. I shortened a 3/4" socket, used with a flex-type totque wrench will get to the inside bolt.
 
It should probably be mentioned that properly torqued fasteners do not require much in the way of locking devices
I would venture to say when design was done with cotter-pins it was standard from railroad theory

John
 
I went ahead and ordered ARP 12pt nuts for the Con Rods, Main Bolts and even for the Cylinder Head. I always likes the looks of ARP fasteners anyway.
 
another benefit of using ARP nuts is you can mix and match the different styles of ARP nuts to get the rod weights the same with out removing metal from the cap
Lawrie
 
Or, maybe he wants the comfort of knowing that he will probably not have to look at cotter pinned rod nuts through a picture window in the side of the block.

I would add that some of the head studs used over the years have had questionable integrity, and probably contributed to gasket failures, etc.

I can understand a "show restoration" not having the proper fasteners, I respect that.
But, I also understand that some people drive their cars and have the freedom to add or remove from said vehicle.

John
 
I use Coast Fabrication "Jet Nuts." Aircraft quality and strength, deformed slightly for a friction fit. Many miles and hillclimbs, no probs. www.coastfab.com The also have a wide base that fits perfectly into the flat without gouging.
 
It doesn't seem like lock nuts of any kind would work well in an engine. There is no way that I know of to get a true torque reading on the fasteners unless you can measure the bolt stretch. Would be hard to tell what the friction adds.
 
As John says, castelated nuts were common for years. I workd as a mechanic in a GMC dealership back in the 50's and 60's. Another mechanic had done a complete rebuild on a 503 CID gas engine. A couple of weeks later the truck came back in, the owner had changed oil and several cotter pins came out with the oil, they had broken because of vibration. I was given the job to replace them because the other guy was off on vacation. Not one single nut had loosened, just the pins were missing, they had not been peened in place to prevent them from rattling around.

Castellated nuts have only a few full-diameter threads. IMO they are prone to strip off under high RPM's, and the reason many aftermarket rods were made for A and B engines. I've run stock B rods for years, turning the engine 6200 RPM on a regular bassis, never a problem with them. I never use Loctite or orher means to secure them, if the nuts are torqued tight, they will not loosen.
 
DBSHELTON said:
It doesn't seem like lock nuts of any kind would work well in an engine. There is no way that I know of to get a true torque reading on the fasteners unless you can measure the bolt stretch. Would be hard to tell what the friction adds.
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That is my thought as well. However, you MAY be able to check the resistance the nut offers while it is half way down the stud by creeping up on it with the torque wrench settings than add that to the final torque value. Example, if you measure 12 pounds of torque to get the nut moving, just add 12 pounds to the final torque value prescribed for that application. I dunno, just a thought.
 
I just ordered a set also, thinking they were self locking but turns out they aren't. So just to be very clear about this. Are you installing them without any form of locking device? Do you stake them or anything else?
 
Licensed to kill said:
That is my thought as well. However, you MAY be able to check the resistance the nut offers while it is half way down the stud by creeping up on it with the torque wrench settings than add that to the final torque value. Example, if you measure 12 pounds of torque to get the nut moving, just add 12 pounds to the final torque value prescribed for that application. I dunno, just a thought.
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exactly, add the resistance of the lock nut to the desired torque value. The torque values you are trying to achieve are standard torque values,not based on actual ford testing,cause there wasn't any.Torquing a fastener removes the 'stretch' in the bolt,putting the assembly in tension,basically locking the nut. Cotter pins hold an assembly together but do not maintain a torque value on a nut.Many folks torque,then tighten to the next cotter pin hole..not a good idea,if you happen to exceed its rated torque value you begin to fracture the fastener.ARP? ..anytime it says racing in the name its gonna cost you,thats the difference between racers and the rest of us..racers never ask the cost.
 
rogeroadster said:
I just ordered a set also, thinking they were self locking but turns out they aren't. So just to be very clear about this. Are you installing them without any form of locking device? Do you stake them or anything else?
Click to expand...

anaerobic sealant ( loctite) doesn't set up till its denied air,allowing you to assemble and torque then it will set.It guarantees torque can be set and will be held.Use loctite blue for engine assembly
 
As far as I'm concerned, the main advantage of using different nuts on the rods is those stupid sized originals will be in the trash. Where on earth do you get a socket to fit those bloody things??
 
I have often found the remnants of cotter pins in the oil pan of engines. After sloshing through oil for many miles, the cotter pins fatigue.
 
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