[67drake]

This is on my ‘62 Mercury 260 V8, but figure the question would apply to any make.
I’m rebuilding the 260 for my Mercury. On cleaning the pistons last night I found one of the nuts had fallen off the bolt. I must not have threaded it on enough when I tore the engine down, or my kid needed it for one of his projects.
Anyway it appears to be a 5/16 24tpi nut. Common enough, but worried about throwing balance off just using a random grade 8 nut. Not to mention since there is no washers on these nuts, I don’t know if a rod nut is something unique? Anyway correct me someone if I’m overthinking it.
Searching the internet I have had no luck so far finding a single rod nut. I’d hate to buy a whole set of bolts/ nuts for one single nut. Any ideas?
Thanks.

[steve25]

As long as it's a grade 8 nut of the same thread pitch that's all you need to be concerned about.

Of more concern is the rod bolts.

If this round of assembly is the 5th time there getting torqued up and the motor will be buzzedup above 5k then the bolts should get replaced and the Rods resized as needed.

[Half-Inch Stud]

Keep trying to find/buy a single Rod bolt-nut combo for the nut. The Thread class need be 2B or 3B, not 1B. I would guess 3B.

[Formulas]

I may have a good used Pontiac stock rod nut laying around or on a stock rod, H,Stud has a valad concern on class of threads

I wouldnt worry to much about balance on a near stock build stock balance tolerances are usually quite wide

[steve25]

His 260 cid Ford engine uses 5/16” rod bolts, so the 3/8” nuts from a Pontiac are of no help.

[Sirrotica]

Time to find a wrecking yard that will allow you to disassemble one of their core engines, and get a nut. Or maybe a engine machine shop that has some stock SBF rods hanging around.

[Johnny406]

Grainger

[Stuart]

Does ARP sell single nuts?

[67drake]

Well, after mucho searching, I did find this -
https://www.summitracing.com/parts/a...-8602#overview

The rods were resized when the engine had its only rebuild back around 1980. The bolts/nuts are black , similar to ARP. They don’t look factory. But nothing in that link says they’re “rod nuts”.

[72projectbird]

I'd just get another nut, torque it down and call it good. Unless you're winding the thing up to 7000rpm+ I'd says it's fine.

[67drake]

Originally Posted by 72projectbird

I'd just get another nut, torque it down and call it good. Unless you're winding the thing up to 7000rpm+ I'd says it's fine.

I doubt this thing will ever be above 4500, maybe 5000. Just a stock rebuild on an old cruiser with 3.00 gears and a two speed automatic.

[grivera]

If concerned about weight, remove another nut and match the weight

[72projectbird]

Originally Posted by 67drake

I doubt this thing will ever be above 4500, maybe 5000. Just a stock rebuild on an old cruiser with 3.00 gears and a two speed automatic.

Sounds good.

Don't overthink it. Put another nut on it, torque it like you would any other rod bolts, and run it.

[HWYSTR455]

Tensile strength on those ARP nuts you found are rod bolt/nut territory. Two most common are 180k & 220k.

Places like Crower sell individual rod nuts.

If you're worried about balance, replace them all with the same type so they at least match. You may not have end to end rod 'balance' but it won't negatively impact rotating assembly balance.


.

[steve25]

Don’t even waste one heart beats worth of time over any concern about balance!!

Some high end race motor builders intensional over balance or under balance a motor by a easy 3 times more then what a nut that size weighs!

I can’t believe some people are even bothering to mention anything about it.

[67drake]

Thanks guys. I found a seller selling individual ARP nuts, without paying Summits $11 handling charge,so I went with that. I won’t worry about the balance, it was just a question. Better safe than having an “Oh Sh*t” later.