Tap and Die

[dnwinberry]

I want to buy a tap and die set that will work with my Model A. Will a standard SAE set work or are most of the Model A bolts fine thread and I will need something else? Could someone please advise me?
Doyce

[2manycars]

Most tap and die sets come with both coarse and fine thread tools. Just specify SAE and not Metric.

[BRENT in 10-uh-C]

To expand on Bill's thoughts, there is also a kit sold under the Craftsman brand called a Master ReThreader that is a great tool for just cleaning up threads during a restoration. We have several sets. The bonus with that set is you get the tool to re-establish the serrations on the bottom edge of Model-A fenders.

For my machine shop, I just made a Tap Stand (like pictured below) that I needed because we are often fabricating or modifying something (i.e.: V8 clutch conversion on flywheel) so it will allow us to quickly grab the proper sized drill and the tap instead of looking on a chart and then locate the correct index set.

.

[Kevin in NJ]

There are thread tolerances.

The common tap and dies you find today will create a looser fit thread then many found on the A chassis. So if you use a 'normal' tap you buy in the kits at Sear's you will end up taking out a small amount of material. This will cause a looser fit.

You find the tighter threads in places you would think like the rear axle housing to pumpkin threading. They are tighter so they will hold without lock washers and will not allow leaks. If you have a NOS bolt going into a NOS housing I doubt you could go half way by finger. Slightly used you can get to maybe 3/4 the way. If you just clean the threads in the housing with a tap you can go all the way down by finger. Clearly not a good thing.

You will find the tighter tolerance in most of the nuts and bolts on the chassis. It is also for the studs on the block. If you tap them you loose out on surface area for the holding the studs and that is probably important if you plan on using a fairly high compression head.

You will also find the tighter tolerance threads in other places. The rods that go from the firewall to the radiator are done with the tight tolerance threading. This makes sense. When you are putting each end into a U shaped hole the tightness prevents the nut from getting off center.
Incidentally, those rods are where I learned about the tighter tolerance threading. I thought it odd the threads were taking off so much clean metal. Then I noticed the nuts wobbling so much more. Then I took one and clean the threads manually and put the nut on and noticed how much better it worked for the job. Then I asked questions.

Now I hand clean most of the threads with a pick or a wire brush. Way more work, but it is about function. I want to drive my car. So on my car you will find some pitted nuts and bolts as they were chosen for there thread fit. Especially on the rear axle, it seems the nasty ones were the ones with thing best thread fit.

[slammin]

If you are concerned about loose fits, the best die to buy is split with a set screw to adjust the amount of material removed. This link shows a 1/2-20: /www.mscdirect.com/product/details/03775301
They are more expensive than the hardware store dies. Most thread call outs ask for a class 2B thread. The tighter tolerance is class 3B. Class 3B is not widely used in production parts. If a member has any original Ford prints for Model A components, please check for thread class. I'd be surprised is you find 3B. The fit difference between 2B and 3B is only a few thousandths. The all thread you buy at the hardware store is probably closer to a 1B thread, loose. Good for bolting lumber together, but not for most industrial applications.

[dnwinberry]

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Thanks everyone for the info. At the current time, I've just found that there are a couple of places that I can't get the screws to go back in. I suspect they've been cross threaded. One is in the yoke that the steering columns clamps to under the dash. Another is one of the screws that attach the dash rail. I have also found that the holes for the center hood rod bracket appear to be stripped out. How is the best way to fix that?
Doyce

[100IH]

Limited help here. If the threaded hole is through or open on the other end, tap from the other end. Not a help for blind holes. In dry or blind holes, a very small round file and a magnifying glass can be used to fix/remove the crossed threads.

[slammin]

Depending on the application, the best way to repair damaged internal threads is to use a heli-coil insert. Kits can be purchased that include the appropriate size drill, a Heli-coil tap, the inserts and a tool to install them. The Restorer had an article in the early 2000s on their use. For external threads, its a lot more difficult.

[Kevin in NJ]

Originally Posted by dnwinberry

Thanks everyone for the info. At the current time, I've just found that there are a couple of places that I can't get the screws to go back in. I suspect they've been cross threaded. One is in the yoke that the steering columns clamps to under the dash. Another is one of the screws that attach the dash rail. I have also found that the holes for the center hood rod bracket appear to be stripped out. How is the best way to fix that?
Doyce

Those screws, like most of the body screws, are the tolerance we see today.

The yoke under the dash you will have to try and save by careful tapping. Kind of hard to do much with that bracket as it is riveted then soldered on the tank. An alternative is to use the late steering drop that attaches under the dash.
Because of the solder you have to be careful with putting heat on the bracket like trying to weld on parts to fix it.

[BillLee/Chandler, TX]

When you get to the screws that hold the floorboards in, you will need a 12-24 tap to clean out the threads in the d-nuts. Since this is a non-critical area, re-tapping to clean the threads is just fine and makes assembly/dis-assembly a lot easier.

A 12-24 is NOT a very common size being between a 10 and 1/4" and you will have to look for it. I am not sure if that size machine screw is used anywhere else on a Model A.

[mhsprecher]

Thanks for the tips, guys. I have wanted to do this for a while.

[BRENT in 10-uh-C]

Originally Posted by slammin

If you are concerned about loose fits, the best die to buy is split with a set screw to adjust the amount of material removed. This link shows a 1/2-20: /www.mscdirect.com/product/details/03775301
They are more expensive than the hardware store dies. Most thread call outs ask for a class 2B thread. The tighter tolerance is class 3B. Class 3B is not widely used in production parts. If a member has any original Ford prints for Model A components, please check for thread class. I'd be surprised is you find 3B. The fit difference between 2B and 3B is only a few thousandths. The all thread you buy at the hardware store is probably closer to a 1B thread, loose. Good for bolting lumber together, but not for most industrial applications.

Since Kevin mentioned the Rear End Housing, I pulled up my print to show the thread specification. Actually it is Class IV ...tighter than even Class III.

.

[Y-Blockhead]

If just cleaning up threads I prefer to use a Thread Chaser instead of a tap or die. Less metal removed...

[CarlG]

Originally Posted by BillLee/Chandler, TX

When you get to the screws that hold the floorboards in, you will need a 12-24 tap to clean out the threads in the d-nuts. Since this is a non-critical area, re-tapping to clean the threads is just fine and makes assembly/dis-assembly a lot easier.

A 12-24 is NOT a very common size being between a 10 and 1/4" and you will have to look for it. I am not sure if that size machine screw is used anywhere else on a Model A.

I cleaned out all the floorboard D-nuts with the 12-24 tap and put all new screws in. In only a couple years, everything was back to where it was when I started. I then bought the stainless set of screws that the vendors offer. Now everything is just like new when I take things apart.

I do think that there are a couple of D-nuts on the firewall that are 12-24 also.

[briphaeton]

Threads has change slightly over the years, 1924 Original American (national) screw thread standard, then to American (national) thread system in 1935 to today's thread, Unified and American (national) screw thread of 1948- mostly rounding off the crest and root. I agree with Terry and others using a re-thread kit is best for our Model A's.

[BILL WILLIAMSON]

In a pinch, grind grooves in a bolt, with a cut off tool. It will clean threads nicely.
Bill Makeshift