MTFCA Forum

Good morning All,

I am working on a 1912 engine and should like to clean up the brass magnet clamping screw thread in the flywheel.
As I was looking for a tap to do this at my usual dealer and couldn't find it . The 14/24 tap or the 1/4-24 tap was unknow.
Where can I find this? (I am living in Belgium)
What does it mean 14/24? Is 24 the number of threads on one inch? Where stands the 14 for?

Thanks
Andre
Belgium

1/4 - 24 = One Quarter Inch Diameter 24 Threads Per Inch = .250 inch diameter 24 TPI

14 is a screw size. It is not often used in modern times, as a machine screw. Machine screws up to size 10 are still common in the US.

24 is the number of threads per inch.

https://www.mscdirect.com/product/details/04439451

There is also a machine screw size of 1/4, which is one quarter inch outside diameter. They are different.

Which one are you needing? Old ring gear on a new repro. Email me I can hook you up. Dan

Dan,
I just send you a Email
Andre
Belgium

Good of Dan Hatch to fix you up with the correct tap.

The brass screws are made of an obsolete thread type, so uncommon to have easy sources to find one.


Later mfg. of reproduction ring gears got the thread i.d. wrong and used modern 1/4" x 24 tpi. So you have to know early flywheel without gear or original ring gear being reused, use the #14 x 24.

If new reproduction ring gear, use 1/4" x 24.

And they are close - a #14 screw is .242" (or 6.145 mm), 1/4 is .250 (6.35 mm). Just enough to get you in trouble!

It is true that 1/4"-24 is an odd thread, but it is STILL a standard thread. It has also long been referred to by bikers as the "Harley Bastard Thread", which, as both a machinist and a biker, has made me chuckle.
If you have a Machinery's Handbook, and you look up different threads, you will find 1/4"-24 right in the selection for all the other standard threads. It is true it is little used now, but that doesn't mean it is NOT a standard thread. It still is, and taps and dies are widely available for them, and can be ordered almost anywhere.
I would be sure to order "BRONZE" screws, instead of brass, as they are about twice the strength. Bronze hardware can be ordered through marine supply houses.
Just for info, a list of STANDARD 1/4" THREADS:
1/4-20
1/4-24
1/4-27
1/4-28
1/4-32
1/4-36
1/4-40
1/4-48
1/4-56

Bill, read the thread again, I think you missed something. Dave

14-28 Original thread size,We make them and have about 20 k of them in stock, Bob

Dave, if you install 1/4-24 screws, I doubt you will even notice anything installing them. They will screw right in. The .006" difference between them is invisible when you take regular tolerances into account.

I read somewhere that the drawings were misinterpreted and 14 was misread as 1/4 or 1/4 was misread as 14, I don't know what the out come was. KBC Tools has them that is where I got mine.

Thanks all,
very interesting all of the information.

I had the 1/4-24 screws at home and tried to use them on a 1912 flywheel. May be they will go in but the one I tried was very hard to turn and I was afraid to break it.
I ordered the 14-24 screws and will go by that as they arrive.
At the same time I ordered a tap for the 1/4-24 screws, it already arrived.
For this engine I will go with the 14-24 screws but I am wondering for the future if I can use the 1/4-24 tap to clean the 14-24 threaded holes and use the 1/4-24 screws. Will I not infect the thread by doing this? Thread numbers are the same only the diameter is a little bigger.

Regards
Andre
Belgium

Andre' ; I think that you can use the 1/4 -24 tap to clean the 14-24 holes in the flywheel , and if needed in the Ford ring gear with no problem .
Toon

I know that there are MANY more knowledgeable people on here than me, and I admit that I have had no experience with the flywheel magnet screws in question at all. That being said, I would NOT try to rethread the holes in the flywheel to fit the incorrect screws. I think that for what they have to do, they should be done correctly. Get the correct screws. Toon, you may well be correct, but I wouldn't chance it since the correct screws are available. No disrespect intended at all, JMHO. Dave

The right screws arrived this morning. They went strait in, no cleaning was needed.
I will go by this and will try to use the right screw every time it is possible.

Take care.

Andre
Belgium

After crunching some numbers, charts, parts books and the famous blueprint I have come to this conclusion: All the parts books from the beginning call for a 1/4" screw displayed as .2 25/32 which converts to .206, a standard 1/4 24tpi would convert to .250. With the screws displayed in the parts books @ .2 25/32 and the standard 1/4-24tpi there is a difference of .054. That accounts for a very loose fit. A #14 is far smaller again @ .182 excessively small. The famous blueprint displays a number that can be interpreted as 14 or 1-4 or 1/4, the display appears to be 1-4 the decimal spec reads max .242 which would indicate this to be a special bolt. The 1/4" thread in the flywheel would be a true standard 1/4" @ .250, the special bolt at .242 would allow for some reasonable clearance about .008. I don't think there is a big mystery between #14 screw, the standard 1/4-24 thread in the flywheel and the special bolt, just forget about any reference to #14. The threads in the flywheel are 1/4-24 and have been that way from the beginning, the screws are special and also have been that way from the beginning with about .008 clearance. Some jobbers manufactured special oil paddles in lieu of the magnets and shipped with the kit 1/4 20tpi to re thread the flywheel to fit the kit. The. jobber has recently converted kit to 1/4 24tpi screws. This means that there are some flywheels out there that have been re threaded with 1/4 20tpi.

with all due respect, David, there is no good place to start to say where you have gone off the rails with this, so will simply post this and be gone. A #14 screw has a basic diameter of .242, regardless of thread pitch, and the Ford drawing says what it says, and that is why 1/4-24 screws will not fit either early flywheels or original starter rings. Only #14-24 screws will. At the time, they were not special, they existed, ASME spec'd and they were the original, correct screw as defined on the drawing (Ref: http://pages.cs.wisc.edu/~bolo/workshop/thread.html courtesy Jerry VanOoteghem). They are "special" now per ANSI standards only because they are obsolete for new design.

With credit to: Mr Darren Wallace

Scott I must admit there are many errors in my report, I was reading from the wrong charts. I understand the screws are #14 24 I have an original screw and that is what it measures. 1/4 24 is somewhat larger and would not fit. Some time ago I had learned that the screws were 1/4 24 and I chased the threads, now my flywheel is a clear 1/4 24. I thought I was just chasing the threads however I was removing material and enlarging the threads. There are some issues of concern firstly, a post above makes note about #14 28tpi? There is also mentions of using 1/4 24 tap to chase the threads, this is what I did and I enlarged the threads which now has a very loose fit. The next point, in all the parts books part number 3278 lists the screws as .2 25/32 this converts to .277?? This part number is used through all the series.
Reviewing the blueprint it is clearly a #14 screw, but what is this .2 25/32 = .277 screw in the parts book?

2 23/32" LONG per Ford drawing

I feel so inept but but also enlightened I was so focused with the diameter that the length didn't enter my mind. The period in front of the description is there before all entries and I hadn't noticed that.
It does say 2 25/32 X 24 tpi. All the mystery is now cleared up. For my collection I am going to seek out a #14 X 24 tap, the catalog only lists a tap but not a die hopefully I can find one. My next flywheel will get chased with a #14 instead of a 1/4. Thanks for your patience with me.

.... ...