Connecting Rod Torque

[Roadster Rich]

As the work goes on on my other thread "dropping the pan", I have a question for you engine experts.

Here is a picture of my connecting rod nuts holding the cap.
Rear Cork Seal 45.jpg
They are not the typical castle nuts. When I did the engine work back in '66, my dad got these nuts for me from his business.

The question is, do you think I should recheck the torque on all of the connecting rods now, and what torque should they be?

All seems quite tight. Turning the front pulley back and forth shows no discernable slop at all. Just want to know if you think I should torque these and the main bearing caps?

[J Franklin]

If the pan is off you should inspect the bearing and crank surfaces and journal for roundness and adjust the clearance. I would torque the nuts to 35# with a bit of locktight on re-assembly to give piece of mind.

[Kohnke Rebabbitting]

A normal Model A rod nut is torqued to 40 foot pounds, and then pull to the key hole, if need be, and that is normally not over 45 foot pounds, or so.

[Jim Brierley]

I would go to 45, those are better nuts than the stock castellated ones. The mains are probably OK but wouldn't hurt to check them. Not a bad idea to check both main and rod clearances while you have it down.

[Russ/40]

Those are aircraft grade. They aren't going anywhere.

[BILL WILLIAMSON]

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Originally Posted by Russ/40

Those are aircraft grade. They aren't going anywhere.

Russ,
Yup, you know your nuts. I used those on old Jaguars. With the dumb cottered nuts, centrifugal force would break off a bent cotter end, it would make it's way through the pan screen, somehow pass through the rotor type oil pump without breaking it, and end up stuck under the oil pressure relief valve on the filter base on the side of the engine, causing LOW oil pressure. This was a common occurance. Low oil pressure was ALWAYS either this, or failure of the DANGED OIL PRESSURE SENDER. I still remember the part #--PT 1801/06!! Bill W.

[Kevin in NJ]

Do you see 3 threads showing?

Or at least 1 whole one?

These nuts need to be fully engaged into the threads to work. If they are just on the edge then they will not be right.

BUT

You have to torque them different. Since the locking portion is creating more friction they will give a false torque, you think you got 40 lbs, but it will be less. Hopefully they were put on till good and tight by a guy who knows how to do equal torque, not using a torque wrench to 40 lbs.

Personally I would take those off and go back to correct original nuts that have not been chased with a tap and torque like recommended. The originals work fine last a long time if they are done right.

[dwollam]

Bill, you mentioned breaking cotter pins. I had that happen on most of the cotters in a DB 4cyl. engine. It was because I used cheap cotters from Harbor Freight. I took them all out and used Dorman cotter pins and have never had one break. The cheap ones were way too brittle. A couple bends and they would snap. Not so with the Dormans. I found my cheapness did not pay off! Fortunatley no damage from them.

Dave

[dave in australia]

These are metal lock nuts. To get the correct torque, use your torque wrench to establish how much torque is required to turn the nut on the thread. Start with a low setting and increase it a little at a time until the nut turns. This is known as running torque. Then add this figure to the listed torque to give you the required torque wrench setting.
eg- you establish that it takes 9 ft/lb to turn the nut on the thread. Your required torque is 45 ft/lb. Add 9 to 45 and the required torque wrench setting is 54 ft/lb.

[BILL WILLIAMSON]

Kevin, Dave, & dave,
I'm constantly AMAZED at the stuff I pickup here. We all have picked up stuff from others, from experience, from trial & error, succeses, & failures & it's neat we can share them.
A friend had an M.G. engine with the lower end torqued up on a stand upside down. Three days later, craaak, kapow, zing, bang----a new repro rod bolt popped, sending the end & the nut like a ROCKET!! Next morning, 2 more had let go overnight!! WEIRD! A little research & he replaced them with USA made bolts for a 200 CU.IN. Ford Falcon. Case closed! Bill W.

[dave in australia]

Originally Posted by BILL WILLIAMSON

Kevin, Dave, & dave,
I'm constantly AMAZED at the stuff I pickup here. We all have picked up stuff from others, from experience, from trial & error, succeses, & failures & it's neat we can share them.
A friend had an M.G. engine with the lower end torqued up on a stand upside down. Three days later, craaak, kapow, zing, bang----a new repro rod bolt popped, sending the end & the nut like a ROCKET!! Next morning, 2 more had let go overnight!! WEIRD! A little research & he replaced them with USA made bolts for a 200 CU.IN. Ford Falcon. Case closed! Bill W.

With the MG rods, this is only an idea and not a deffinate, but. An MG is British and would most likely have whitworth threaded fasteners. A lot of SAE fasteners have the same thread pitch, but the included angle of the thread is 5 degrees different. So if the nuts were SAE, and they do fit, it doesn't make much difference in general, but on high stress parts like rod bolts, the threads are only touching on a small surface area of the thread. This will raise the internal stresses around the threaded area and can cause premature failure, as id did in this situation.
Just and idea on what may have caused the failure and it also raises a point of discussion on fasteners.

[Kurt in NJ]

The cotter pins on a rod can't just have the ends bent, it needs to be cinched tight to prevent it from moving ---otherwise it will move in the hole and wear will occur leading to it falling out.

[redmodelt]

The more torque you put on the threads of the non-replaceable rod studs the more you pull the threads and make them trash. I would go back to stock nuts and torque to 35 which is what all the books I have seen suggest. If the cotter pin hole is blocked to the point where pulling just a little more wont expose it, I would remove the nut and ether swap them around or file a little off till it lines up with the hole at 35 or just a little more.
I was under the impression that most pinch type nuts were a one time use any way.

[J Franklin]

It always seems that people like to over-tighten fasteners. I had a friend with the last name of Armstrong but we nicknamed him Strongarm. He was always stripping and breaking fasteners. There is not much load on rod nuts or bolts as they only drag the rod and piston down when starting the engine, otherwise they are there to keep the clearance. Some model T's and maybe A's also were fit with spring loaded caps that would keep a constant clearance as the babbet wore out.

[Roadster Rich]

Wow, so much info, that now I don't know whether I should touch anything. I guess it must have been done correctly when I did this rebuild with my dad at age 14. They have held and are tight. I have some plastigage but since the engine was not making any bad noises, seems to be tight without play, maybe I am better off buttoning it back up without going any farther.
I always thought that once you had met the break away torque of a fastener, when you hit the seating position, that you DID NOT have to add any more torque and used the same as you would for a looser nut. Now confused but am doing some research so thanks for that advice. Also if you really should not reuse these nuts, I guess I will leave good enough alone.
Always amazing at how much you can learn from all you guys on this site!

[J Franklin]

If indeed you can not reuse the nuts they can be replaced with new nuts of the same type. You can get a good indication of the rod clearance without removing the caps by taking notice of looseness while manipulating the bearing side to side and back and forth on the journal after cleaning things up with solvent to rid the oil cushion. it should not have slop or noise. I would suggest if you don't feel competent to do a check you might contact an engine rebuilder to do it. I had a T engine dismantled tightened and re-gasketed for a reasonable fee. I was planning to sell it and that gave me a list of all the existing clearances to offer with the engine, which proved ok and was set up with the bearings all set to specs. A head in the sand only works for an Ostrich!

[dave in australia]

You can re-use metal lock nuts, you just check them to see if they still have resistance when attempting to do them up. There is a listed resistance that they should meet to be considered serviceable, if they don't meet it, they're unserviceable. We reuse metal lock nuts in aviation all the time. If you do replace them, do not use the ones with the nylon insert, the nylon may react with engine oil and the heat, go soft, and lose its locking resistance.

[BILL WILLIAMSON]

Originally Posted by dave in australia

With the MG rods, this is only an idea and not a deffinate, but. An MG is British and would most likely have whitworth threaded fasteners. A lot of SAE fasteners have the same thread pitch, but the included angle of the thread is 5 degrees different. So if the nuts were SAE, and they do fit, it doesn't make much difference in general, but on high stress parts like rod bolts, the threads are only touching on a small surface area of the thread. This will raise the internal stresses around the threaded area and can cause premature failure, as id did in this situation.
Just and idea on what may have caused the failure and it also raises a point of discussion on fasteners.

dave,
It was NOT a thread problem, the bolts just BROKE about 1/4" above the threads. He described it like a 22 rifle sound!! Bill W.

[dave in australia]

Originally Posted by BILL WILLIAMSON

dave,
It was NOT a thread problem, the bolts just BROKE about 1/4" above the threads. He described it like a 22 rifle sound!! Bill W.

Hmmm, could have been a problem with the hardening process. When I was an electroplater, I worked in the standards lab. One of my jobs was to assess the hydrogen embrittlement of each plating tank. The test piece was plated, and then a high tensile load was placed onto the test piece. If any embrittlement was in the piece it would snap suddenly within 200 hrs. It sure does go off like a rifle shot, and usually when your doing something else in the lab.

[BILL WILLIAMSON]

Originally Posted by dave in australia

Hmmm, could have been a problem with the hardening process. When I was an electroplater, I worked in the standards lab. One of my jobs was to assess the hydrogen embrittlement of each plating tank. The test piece was plated, and then a high tensile load was placed onto the test piece. If any embrittlement was in the piece it would snap suddenly within 200 hrs. It sure does go off like a rifle shot, and usually when your doing something else in the lab.

dave,
Years ago working on Jaguars, lots of Dunlap chrome wheel spokes would break at the hub end. They stopped chroming the last 3/4" of the spoke & just sprayed it silver & breakage stopped. Sounds like what you describe. Bill W.