Rod nuts

[Bruce Lancaster]

On the integral bolts...the big risk is that some gorilla 50 years ago severely overtightened them and stretched the bolt, making it a possible time bomb ready to saw your engine in half somewhere down the road.
My thought on this...clean the thing as thoroughly as possible with solvents and those little toothbrush things. Run on a new good quality nut, a nut with no tricks like self locking or nylock. Maybe get a test nut from ARP rather than worry about what's at the hardware.
The nut should go on smoothly and all the way up and down the threads with no areas of funny resistance OR sudden looseness that might indicate a stretched out area. The only permissible work is removal of small problems like a ding in a thread from when the rod was dropped by a mechanic in 1952...NOTHING that reshapes the thread.
If you get indications that one area (generally around where the nut lives as tightened) you CANNOT fix it by running a die over it...that will cut away the metal rearranged by the stretch and simply conceal the damage to fit and core strength of the bolt, giving you a nice feel on your timebomb.

[Kohnke Rebabbitting]

In over 88,000, 500 4 times a year, or every 3 months Model a Rods rebuilt in 53 years, I have yet to see a broken Model A rod bolt. These were all Spun Poured. We do not do T, A, or B rods, anymore, as there is no money in them.

Bolts will strip before they break. Bad threads, maybe 4 to every 500 rods.

When you put a original Model A Rod nut on, 21/32nds, or a 11/16, or 5/8's, the bottom of the key slot must be even with the bottom of the hole. If it isn't, the space left is what is missing in shims that should have been put in by the Rod builder, to make up the difference in the cap metal that is missing. That is the kind of shoddy work we had to compete with in later years, and other things that are apart of a rod built right so we gave up on the T,A, and B Rods.

NEVER put a nut on ANY bolt with out oiling. You are asking to ruin both. Some bolts go bad in the working area of the nut and bolt, from over tightening, and running dry, as in no oil!

We torque to 35, and then pull for the key hole. No need to pull over 40 foot pounds.

After 45, you can pull threads if they have already started to umbrella.

We still do all other bearings.

Herm.

[mantta]

I put Marsden nuts on mine a few years ago, no problems.

[RawhideKid]

Originally Posted by Kohnke Rebabbitting

In over 88,000, 500 4 times a year, or every 3 months Model a Rods rebuilt in 53 years, I have yet to see a broken Model A rod bolt. These were all Spun Poured. We do not do T, A, or B rods, anymore, as there is no money in them.

Bolts will strip before they break. Bad threads, maybe 4 to every 500 rods.

When you put a original Model A Rod nut on, 21/32nds, or a 11/16, or 5/8's, the bottom of the key slot must be even with the bottom of the hole. If it isn't, the space left is what is missing in shims that should have been put in by the Rod builder, to make up the difference in the cap metal that is missing. That is the kind of shoddy work we had to compete with in later years, and other things that are apart of a rod built right so we gave up on the T,A, and B Rods.

NEVER put a nut on ANY bolt with out oiling. You are asking to ruin both. Some bolts go bad in the working area of the nut and bolt, from over tightening, and running dry, as in no oil!

We torque to 35, and then pull for the key hole. No need to pull over 40 foot pounds.

After 45, you can pull threads if they have already started to umbrella.

We still do all other bearings.

Herm.

Hey Herm, As you say "the bottom of the key slot must be even with the bottom of the hole", what should be done if this can not be due to wear on the babbit and removal of shims to bring the bearing surfaces back to spec with a well used engine with still serviceable babbits?

If removing the shims brings the holes below the slot, will replacing the cotter pin still work?

[hardtimes]

Hey Herm,
Thanks for your factual contribution , about never having seen a broken A/B rod bolt in many thousands of reworked rods ! And, only a small number of stripped rod stud/bolt threads.

I wonder have you ever seen a 'broken' A/B rod ?
I've talked to guys who build/race A/B engine and submit them to more severe treatment then most would believe possible. I have not come across one such source who has seen a broken A/B rod.

I hear guys say, at times, that the A/B Ford rods are not that strong...go figure ?
I've also been informed that (in days gone by when the stock nuts were used) the NUT /system that Ford put onto the A/B rods, were the source of such bad rep that was ascribed to the A/B rods..when the stock nuts came lose. IMO, that's why builders/racers use more modern tech made nuts on whatever rods are used.

[colin1928]

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I wonder have you ever seen a broken A/B rod ?

Yes I can show 1/2 a dozen broken X style A model rods
H style not so much

[Synchro909]

I wonder why they bother making new rods if the originals didn't break or fail some other way at least now and then.

[BILL WILLIAMSON]

IF rods never BREAK, how come we've heard HORROR stories about BIG HOLES in the blocks??
"Maybe" it wuz the work uf a little guy in there, with a BIG HAMMER????
Heard of one, where they made a patch for the hole, shoved the piston to the top, & drove IT!!! At my Wrecking Yard, we had a '52 BUICK like that!! It was RUNNING & DRIVING, when it was wrecked!
Bill Bang

[Kohnke Rebabbitting]

Originally Posted by RawhideKid

Hey Herm, As you say "the bottom of the key slot must be even with the bottom of the hole", what should be done if this can not be due to wear on the babbit and removal of shims to bring the bearing surfaces back to spec with a well used engine with still serviceable babbits?

If removing the shims brings the holes below the slot, will replacing the cotter pin still work?

No matter how many shims are used to get the nut set right, the key should be able to lock the nut for at least .030 thousandths of shim removal. But in any rod, after .006 thousandths of shim removal, the rod is much out of round where much of the oil escapes, out the sides in a pressure system and makes an oil burner, and the sides of a dipper rod are not touching either.

So if you don't replace the rods with ones that are the right fit from the start, and after you remove .006 shims and run it that way, what does it do?

The Crank starts going flat, because it is only touching top and bottom, and the sides not at all. A crank pin can not remain round that way.

If you have to pull any shims on a new rod, either the Crank is not ground
right, or the rod bore is off.


In a pressure system, a rod with a full circle groove on the inside is the best. there were a few that had that. But most had half grooves, either in the rod, or cap.

The reason is with a full circle groove, where the groove runs on the crank,
doesn't wear. So if you had to replace the rod, it would not fit from the groove area that is still standard.



Herm.

[Kohnke Rebabbitting]

Originally Posted by hardtimes

Hey Herm,
Thanks for your factual contribution , about never having seen a broken A/B rod bolt in many thousands of reworked rods ! And, only a small number of stripped rod stud/bolt threads.

I wonder have you ever seen a 'broken' A/B rod ?
I've talked to guys who build/race A/B engine and submit them to more severe treatment then most would believe possible. I have not come across one such source who has seen a broken A/B rod.

I hear guys say, at times, that the A/B Ford rods are not that strong...go figure ?
I've also been informed that (in days gone by when the stock nuts were used) the NUT /system that Ford put onto the A/B rods, were the source of such bad rep that was ascribed to the A/B rods..when the stock nuts came lose. IMO, that's why builders/racers use more modern tech made nuts on whatever rods are used.

I had seen a Model A Rod that had one side gone off of it when I was a kid, at a swap meet, but it didn't look like an engine had done it.

Those that say they are not very strong, have not tried to align one.

If a rod cap comes loose, it is always the Mechanic!

Herm.

[hardtimes]

Originally Posted by Synchro909

I wonder why they bother making new rods if the originals didn't break or fail some other way at least now and then.

I haven't heard of or seen any such tests results, but it would be interesting to have the A/B rod tested for various strengths, against say an A/B Crower rod !

[katy]

Rods do break, this one, in a 855 Cummins was on a generator set, running at 1800 RPM when it broke.

[hardtimes]

Originally Posted by katy

Rods do break, this one, in a 855 Cummins was on a generator set, running at 1800 RPM when it broke.

Yeah, there have been broken rods through out the automotive history of automobiles. I do not think that anyone would doubt that that's a believable fact.

However, we are talking Ford's A/B rods, and evidently his rods were made pretty tough !

[Joe K]

Originally Posted by Kohnke Rebabbitting

In over 88,000, 500 4 times a year, or every 3 months Model a Rods rebuilt in 53 years, I have yet to see a broken Model A rod bolt. These were all Spun Poured. We do not do T, A, or B rods, anymore, as there is no money in them.

Bolts will strip before they break. Bad threads, maybe 4 to every 500 rods.

When you put a original Model A Rod nut on, 21/32nds, or a 11/16, or 5/8's, the bottom of the key slot must be even with the bottom of the hole. If it isn't, the space left is what is missing in shims that should have been put in by the Rod builder, to make up the difference in the cap metal that is missing. That is the kind of shoddy work we had to compete with in later years, and other things that are apart of a rod built right so we gave up on the T,A, and B Rods.

NEVER put a nut on ANY bolt with out oiling. You are asking to ruin both. Some bolts go bad in the working area of the nut and bolt, from over tightening, and running dry, as in no oil!

We torque to 35, and then pull for the key hole. No need to pull over 40 foot pounds.

After 45, you can pull threads if they have already started to umbrella.

We still do all other bearings.

Herm.

All good advice.

I myself was concerned with my rebuilder providing nylocks on my engine. I asked if there had been any issues to which I got the negative.

"Here" he says handing me a baggie. "You can put the original nuts back on when you peel your first shim if you really want."

Step forward a year or two and I'm still running the "old" engine not yet having done the swap.

Now mind you this is the engine with the rod journals which are 0.005 egg shaped - you set the rods so they just "squeek" as they pass worst dimension to worst dimension. It didn't stay tight long - and very "flubba-flubba" in sound - but OK for the next parade or trip for ice-cream?

I'm taking a short cut on the Mid-Cape Highway on a busy Saturday afternoon. Pretty heavy on traffic (Mid-Cape is like that a LOT of the summer) and everyone is moving along. INCLUDING ME pushing that engine above 55 to not be an obstruction to traffic.

When suddenly - knock-knock-knock-knock out of the engine. I pulled over, the engine had not stopped but was still running. I loafed it home on the back roads but it was plain from the sound that the engine didn't want to be "pushed."

At home dropping the pan I found one of the cotter pins had sheared, and the nut on that one had dropped off and I found it in the oil sump. The rod was being held by one side only.

Note to self: Extreme levels of looseness will cause a knock. And cotter pins are NOT forever.

Of course, me pushing the envelope with a "challenged" engine didn't help. And one can see how sympathetic vibration caused by the near galling condition of my eggy rod journals might contribute to some flexing in this area.

I very quickly gave up on that engine and swapped it out for the rebuild.

And now perhaps 10K miles later after a quick peel on the shims at 500 miles and the nylock rebuild is still going strong?

Knock on babbitt - not.

Final on torque. If it doesn't fail in torquing - then a bolt/nut combination is likely to go the life of the machine without failure. The worse stress a properly designed fastener experiences in its life is the action of assembly.

Of course if the stretch on the bolt is lost due to vibration or externalities - all bets are off.

Joe K

[dave in australia]

Originally Posted by Bruce of MN

Are nyloks used on aero engines internally? I don't know, but it would be a good reference point.

This chart https://www.calpaclab.com/nylon-chem...ibility-chart/ says excellent for motor oil up to 120F. In reality, they are probably just fine at our oil temperatures.

Nylocs are not used in any aero engine I've worked on. They use either tab washers or metal lock nuts.