I Don't Like Palnuts

[Overkill-F1]

A quick question for you guys about what I should use to lock the connecting rod cap nuts in place.
This is for my '52 F1 with a C1BA/8RT Canadian built engine. The engine came with what might be called tab washers (?). They fit into the con rod cap and the tabs are bent up after torqueing the nuts to lock them in place.
On the left is one of the tab washers that was originally installed in my engine. They have been used twice, during the original build and reused by the previous owner when he rebuilt the engine and can't be reused again.
I ordered new con rod nuts and what I hoped were new tab washers, they shipped Palnuts (as shown on the right in photo).
I got info from the manufacturer of the Palnuts about the suggested torque for these nuts. I only tried 4 of them and two of them failed before I got to the suggested torque of 60 in.lb. (that's only 5 ft.lb.!) I don't trust these Palnuts to stay on the con rods or to lock the con rod nuts.
My question... is it ok to place a jam nut on each con rod nut? (I can get jam nuts locally and are a low profile nut).
Thank, Terry

[Brian]

Terry, Personally, on every engine I build, I just use loctite. I think adding extra lock nuts as you're proposing would, if nothing else, affect the balance.

[aussie merc]

a good high strength thread locker every time

[frnkeore]

Engine manufacturers haven't used a lock on rod nuts, since the 60's.

I would be very comfortable using new grade 8 nuts on the rods, torque to spec.

[35fordtn]

I really like ARP rod nuts they sell for flatheads. I put a dab of blue locktite in the threads even though it’s not needed

[Ken/Alabama]

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I use the same 3/8 locknuts as used on the small block Chevys. Readily available at your local parts house .

[Ronnie]

Chevy is the answer no loc tite.


R

[tubman]

Originally Posted by Ronnie

Chevy is the answer no loc tite.


R

As a "belt and suspenders" type of guy, I have to ask : Is the just because it's not needed, or is there a reason not to use it?

[Overkill-F1]

Thanks everyone for putting their two cents in.
If my memory is right, the new nuts I got are the Chevy ones. So I'll not add any jam nuts.
But, as a '"Overkill" type of guy, I'll use blue loctite.
Thanks, Terry

[Pete]

A fastener that is properly assembled and torqued to spec will NOT come loose.
FRICTION is what keeps it together.
There are NO Pal Nuts, Tablocks, cotter pins, jam nuts, Loctite or weld that will keep it together if it is not torqued to spec on assembly.
Torqueing is only half of it also. The thread needs to be clean and lubed with some kind of thread lube like ARP has. If you don't have ARP lube, rear end gear lube will get by. The face of the nut needs lube also.
LOCTITE WON'T WORK IN THE PRESENCE OF OIL. You need the lube more than the Loctite.

A lot of rod failures can be attributed to tightening with a torque wrench that was out of calibration.

The modern nuts that are refered to as "Chev", "Cat", etc. are called "MARSDEN" nuts.
They have slots on the back and look similar to a castellated nut but the slots are thinner.
The thing that makes them work is a relief on the inside of the face that causes the lands on the back to distort and exert clamping force when the nut is torqued.

For what it is worth, race engine rod bolts/nuts use NO locking method other than friction. Either plain nuts or plain thread 12 point bolts.

[fordwife]

I have been using pal nuts on automotive and aircraft for 60 years. I have yet to see one fail.

[rotorwrench]

Neither have I but then I don't torque them near that tight. It's just a jam nut.

The Robinson helicopters use a butt load of the things since the FAA required a double lock on all flight controls. The nuts used are a damn good lock nut and don't normally need a pal nut so it's just to meet the regs. I usually tighten them snug to the nut and then a bit more to even the flats out with each other. The standard torques for 3/8" fastener would be 29 to 60 in/lb so they are giving you the max torque of a pal nut. I would be closer to 29 in/lb myself.

[35fordtn]

Originally Posted by Pete

A fastener that is properly assembled and torqued to spec will NOT come loose.
FRICTION is what keeps it together.
There are NO Pal Nuts, Tablocks, cotter pins, jam nuts, Loctite or weld that will keep it together if it is not torqued to spec on assembly.
Torqueing is only half of it also. The thread needs to be clean and lubed with some kind of thread lube like ARP has. If you don't have ARP lube, rear end gear lube will get by. The face of the nut needs lube also.
LOCTITE WON'T WORK IN THE PRESENCE OF OIL. You need the lube more than the Loctite.

A lot of rod failures can be attributed to tightening with a torque wrench that was out of calibration.

The modern nuts that are refered to as "Chev", "Cat", etc. are called "MARSDEN" nuts.
They have slots on the back and look similar to a castellated nut but the slots are thinner.
The thing that makes them work is a relief on the inside of the face that causes the lands on the back to distort and exert clamping force when the nut is torqued.

For what it is worth, race engine rod bolts/nuts use NO locking method other than friction. Either plain nuts or plain thread 12 point bolts.

While this contradicts the fact that I have used loctite, I cannot agree more. Even ARP states it is not needed, and highly recomends their lube. I dont build many engines so my opinion should be of little concern

[Ol' Ron]

Been using Chevy nuts for the past 50 years.

[RalphM]

Got a part # for those Chevy nuts? I’m putting one back together now and will try them.

[JSeery]

I think all SBCs use the same rod nuts, maybe the BBCs as well, but don't know about that one.

[frnkeore]

The SBC, 5.7" long rods use 11/32 nuts. The SB 400, uses 3/8's nuts.

[JSeery]

A Chevy man! All my Chevy experience is pre-400. Actually mid-60s, ran a B/A with a SBC for one season and then switched to SBF. Sooo, limited up to date SBC knowledge, LOL. My dirt cars were Ford as well, I always liked to be different!

[cadillac512]

The small journal Chevys...265,283,early 327...used the 11/32" bolts and nuts. When Chevy went to the larger journal cranks (starting with the later 327 and continuing through the 400) all the bolts/nuts are 3/8" regardless of rod length.


Terry

[GOSFAST]

Originally Posted by cadillac512

The small journal Chevys...265,283,early 327...used the 11/32" bolts and nuts. When Chevy went to the larger journal cranks (starting with the later 327 and continuing through the 400) all the bolts/nuts are 3/8" regardless of rod length.


Terry

Hi Terry, with one exception.

The '67 model year Camaro's with the SS/350" option got a large journal unit but still with the 11/32" rod bolts. This was the only time and I believe it was offered only in the Camaro's, it was also the earliest year for the 350"?

(Add) To answer the O.P's question, we use ARP 3/8" rod nuts with a 7/16" socket size, either 6-pt or 12-pt, these are the "AN" series nuts and are far superior to any others. We also have the conventional 3/8" ARP's, 9/16" 6-pt socket with a built-in washer for better seating.

Thanks, Gary in N.Y.

P.S. This little known fact caused much confusion in the aftermarket back then, everyone assumed when they saw the smaller rod bolts it was automatically a small journal unit, caught a bunch of us off-guard! These "only-year" rods were easily identified by a "dimple" under the rod eyes. Here's a shot of the rod, it's the one in the middle!