rod nuts...why the odd size?

slatgrille

slatgrille

Senior Member
Removing the pistons on my engine became quite the job yesterday. Even had to cut one of the connecting rod nuts because I don't have the correct size socket it appears. 5/8 was too small and 11/16 too big! After struggling to remove them all, I read they are 21/32...what's up with that? :mad:

I finally used a metric socket that was the closest fit. Metric...on a Model A...sacrilegious! :eek:

Why such an odd size? Was 'ole Henry trying to make it difficult to work on....

Craig
 
simple
When the Model A easy designed and built the SAE had not standardized on fasteners.

John

PS, I would replace them with modern nuts of proper grade.
 
A quick google search shows brand new sockets 21/32 , in 6 point or 12 point for less than 5 dollars ! I believe I have one from my original 1970 tools that was needed on DC-9 landing gear
 
I seem to recall using a 19mm socket that was just about perfect. Most guys have metric socket sets given to them by well-meaning family members for Christmas and 19mm is a standard size included in such packages.
M.
 
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My A had a little less than 50,000 miles on it when it got it's engine rebuild. All indications were that it was it's first. I had to go buy a 4-point socket. I think I still have it in my toolbox.
 
Gene F said:
My A had a little less than 50,000 miles on it when it got it's engine rebuild. All indications were that it was it's first. I had to go buy a 4-point socket. I think I still have it in my toolbox.
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Four point sockets are for the main bolts. They are 9/16 square.
 
Last year I picked up 19/32” and 21/32” sockets off Amazon for very reasonable cost. Got into the engine and someone had already replaced those nuts with 5/8”. Go figure.
 
johnneilson said:
simple
When the Model A easy designed and built the SAE had not standardized on fasteners.

John

PS, I would replace them with modern nuts of proper grade.
Click to expand...

Me too! If building a high performance engine, the castellated nuts will strip off at high RPM's as they only have about 4 good thread on them.
 
Should I obtain grade 8, or will grade 5 suffice? It's not a high performance rebuild. I've found 5/8x7/16-20NF castle nuts on Amazon. This engine was built by my uncle in 1990 just before he unexpectedly died. His son never started the engine, but used the crank to keep it 'free'. I was the one to get it started. I've run it for the past 2 years and it has a knock. I plasti-gaged the con rods previously and they were all .0015. I changed the timing gear because the original had chipped teeth everywhere. That didn't change the sound. A club member thought it sounded like a valve noise.

Rather than chase it down little by little, I decided to 'go-for-broke'. Pistons and rods are out and the cylinders look good albeit, very shiny. I plasti'd the rear main and it's also .0015. I replaced the broken 'drain-back' tube and will measure the other 2 mains soon. I plan to remove the valves and guides as well as hone the cylinders. Only issue with the pistons is that #'s 1,2,4 have what looks like re-enforcement metal that curves through the inside, but #3 is plain. I don't suppose that could be causing the knock???? Everything inside the block is clean...no 'junk' in the oil, no broken parts, etc. While apart I've painted the head, intake manifold, valve cover and various fasteners. The bearings aren't burned or scored, BUT...there are a couple spots where little pieces are missing. The engine is in the car and I don't plan on removing it. I'm hoping there is an 'off-the-shelf' concoction I can use to fill the small gaps in the babbitt and file/sand down. I know it's not the ideal fix, but this vehicle is not going to be 'pushed' nor make long trips.

Thanks for all the comments so far!

Craig
 
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Please do not take this as an insult, but in my opinion you should pull the engine and do a proper job of overhauling it. There is nothing that can replace the missing chunks of bearing besides a new pour and line bore, or inserts.

A knocking noise can come from many different sources. If the rods are bent the big end bearing of the rod will slap back and forth causing a knock. Could also be loose piston pins or loose main bearings.

The metal added to the pistons was done in a few years of Model A production. Consult the Service Bulletins for information. Modern pistons and rings are the correct way to go. Hone the cylinders as you plan. Put modern valves, new guides (that just push in and are held by the spring) and new springs and keepers. Lap the valves just enough for a uniform grey ring. Have the rods checked for straightness and straightened if necessary. The pistons come with new pins but check the fit in the rods. Should be a push fit with no slop at all. Measure the bores to check for taper or excessive wear. If the block is not flat on top, have it surfaced. Same with the head.
 
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If someone knowledgeable thinks the knock might be valves, check to see if you have adjustable lifters. If not, then you might consider going the extra 10 yards and pulling the engine to install them. Presuming your uncle ground valves when he did the engine, who knows if he followed up by properly adjusting the valves (which, for non-adjustable lifters, has to be done by grinding the valve stems - quite a bit of a pain). I did an engine last year that had the valves all over the place, from 0.012" to 0.029". Replaced with adjustable lifters and problem solved.


Sounds like one piston may have been replaced during previous rebuilds. That can affect relative balance of the reciprocating parts.
 
I will second the addition of adjustable lifters.

I forgot to add that you can probably buy a 21/32 socket at the local auto supply store.
 
Plenty to think about gents...no insult taken, thanks for the input! I just got back from the hardware store and bought 8 new 7/16-20 slotted nuts, grade 5. There's more 'meat' on the hex than the domed castle nut and they fit an 11/16 socket. I'm about to go out and remove the valves...I'll see what I come up with to remove the guides so I don't have to wait for a vendor to ship the special removal tool.

Although a simple engine, for me, WWII jeep engines are easier to work on...no 'special' tools needed. Insert bearings, adjustable lifters, guides pressed into block and straight shaft valves for easy removal, oil pump externally mounted, distributor out of block, not head. But, alas, they are 'newer' and I've done many over the past40 years...maybe it's the babbitt that has me apprehensive...more to come!

Again, thanks for the experienced suggestions!
 
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slatgrille said:
Plenty to think about gents...no insult taken, thanks for the input! I just got back from the hardware store and bought 8 new 7/16-20 slotted nuts, grade 5. There's more 'meat' on the hex than the domed castle nut and they fit an 11/16 socket. I'm about to go out and remove the valves...I'll see what I come up with to remove the guides so I don't have to wait for a vendor to ship the special removal tool.

Although a simple engine, for me, WWII jeep engines are easier to work on...no 'special' tools needed. Insert bearings, adjustable lifters, guides pressed into block and straight shaft valves for easy removal, oil pump externally mounted, distributor out of block, not head. But, alas, they are 'newer' and I've done many over the past40 years...maybe it's the babbitt that has me apprehensive...more to come!

Again, thanks for the experienced suggestions!
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Be careful re: the guides. Standard Model A valves have a flair on the bottom for the valve keeper. You can’t pull the valve straight up after removing the keeper and spring like you can on a modern valve. The guide comes out with the valve in place, so you need the special tool to get around the head.

FWIW, I have found that new special tools sometimes need the slot opened up just a hair to allow it to go around the valve stem without scratching. You just need to relieve the edge of the opening, and maybe the sides, with a fine file and sandpaper.
 
Hello, remember first encounter back 1971 with the rod nuts ,wasn’t a common size then, wonder if it was attempt by Ford to keep unauthorized people from working on it , and have to take it back to a Ford agency. The 12/24 screws for floor boards not common either.
 
gdmn...that was my thought too...only authorized Ford dealers would be able to perform major repairs involving engine internals. Kind of an early version of our now Right to Repair legislations taking place around the country.

As for the valves, how do you get the spring compressor tool between the bottom of the spring and the 'keeper' so it can be removed. The damn keepers are the same dia. as the spring. Realized this when I compressed it and only the mushroomed stem was visible...the whole unit was being compressed! Gave that up in a hurry and cleaned the pistons instead.
 
Just for the record, the strength of a bolted-joint in tension is determined by the nut because it has fewer threads to carry a load.
 
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