TR2/3/3A Need Help with a "THREAD SIZE" for a TR3:

[toysrrus]

Need Help with a "THREAD SIZE" for a TR3:

Howdy Folks,

(1st) "HAPPY, HEALTHY MOTORING NEW YEAR TO ALL":

(2nd) I`m in the process of "Re-Assembly" of various Engine Bay component parts etc. I would like to know "What is the "THREAD SIZE" on the "3 STUDS" that are on the "Steering Wheel Bracket" that bolts onto the "Firewall"?

I`m having a heck of time finding the correct nuts!!

Thanx in advance,

Russ

 

[martx-5]

Re: Need Help with a "THREAD SIZE" for a TR3:

If you're talking about the three studs that come through right at the top of the firewall, they are <span style="font-weight: bold">1/4"-28.</span>

Edit: Should be #10 in this diagram.

Sometimes the ends of the studs get messed up, so you may have to run a die on them or use a thread file.

 

[toysrrus]

Re: Need Help with a "THREAD SIZE" for a TR3:

Hi Art,

"Thanx"; Thats exactly what I needed. Man, I guess I have to take the darn thing apart again to chase those threads!

Again, "Thanx" and "Happy New Year".

Russ

 

[DNK]

Re: Need Help with a "THREAD SIZE" for a TR3:

Up late Russ? I'm going to bed

 

[TR3driver]

Re: Need Help with a "THREAD SIZE" for a TR3:

I guess I have to take the darn thing apart again to chase those threads!

Check out MMC item 2667A12
https://www.mcmaster.com/#thread-repair-dies/=aegmj5

These are thread chasers that are literally the same size as the usual nut for that thread, meaning you can screw them on in any place you can install a nut. By leaving off the lock/flat washer while chasing the threads, you can chase far enough that no disassembly is required.

They aren't for cutting new threads, but seem to work very well for chasing damaged threads. Actually slightly better than a normal thread-cutting die, because they tend to form the metal back into place rather than cutting it away.

You'll also want some cutting oil, as the directions say to always use it.

 

[startech47]

Re: Need Help with a "THREAD SIZE" for a TR3:

So cool! I use McMaster Carr all the time and never noticed them. Looks like the robotics club is getting some new tools. Make sure you look at the tight spot dies at the bottom of the page.

 

[DrEntropy]

Re: Need Help with a "THREAD SIZE" for a TR3:

They aren't for cutting new threads, but seem to work very well for chasing damaged threads. Actually slightly better than a normal thread-cutting die, because they tend to form the metal back into place rather than cutting it away.

This is an important distinction. Never use a die on an already threaded stud/bolt. It will introduce stress-risers in the form of a deep cut to the "valley" of the threadds. The thread "chasers" are made so the deformed portions of the thread are literally worked back into the proper alignment.

 

[TR3driver]

Re: Need Help with a "THREAD SIZE" for a TR3:

FWIW, Sears sells a larger set with both fine and coarse threads, plus chasing taps as well as dies, for around $50.

Also FWIW, I disagree with Doc. In the vast majority of cases, any slight weakening caused by using a thread cutting die to chase threads is simply not significant, especially if the die has been used a few times. In this case, for example, you could weaken those studs by 20% and they would still be stronger than the sheet metal they are fastened to. I've been using cutting dies to chase threads for 40 years, and I've never had a fastener fail afterwards.

But in cases where strength IS critical, like head studs or connecting rod bolts, you shouldn't be chasing threads at all. If the threads are damaged, replace them. All too often, the threads are distorted because the underlying fastener has permanently stretched, meaning it is already starting to fail. And even with a proper thread chaser, the previously damaged thread will never be as strong as it was originally.

 

[Member 10617]

Re: Need Help with a "THREAD SIZE" for a TR3:

Does anyone know where to find a good quality British thread guage to use to sort out and determine the thread size of a jumble of bolts? Auto supply stores hereabouts have American thread guages, but nothing for most of the bolts on my TR3.

 

[DrEntropy]

Re: Need Help with a "THREAD SIZE" for a TR3:

Also FWIW, I disagree with Doc. In the vast majority of cases, any slight weakening caused by using a thread cutting die to chase threads is simply not significant, especially <span style="font-style: italic">if the die has been used a few times.</span> In this case, for example, you could weaken those studs by 20% and <span style="font-style: italic">they would still be stronger than the sheet metal they are fastened to.</span> I've been using cutting dies to chase threads for 40 years, and I've never had a fastener fail afterwards.

This ain't a mud slingin' contest, not to be taken as such. So with that:

Yep, Randall, it is likely the fresh cutting of those particular fasteners wouldn't be significant compared to the material they're attached to... but compared to the stresses on the steering box from vibration or shock from road hazards, I'd have concern. They're in tension. Stress risers introduced to fasteners where control kinda counts I'd be erring on the side of caution.

The distinction between "critical application" like head studs and "other fasteners" may be legit but I still wouldn't do it.

 

[Andrew Mace]

Re: Need Help with a "THREAD SIZE" for a TR3:

Does anyone know where to find a good quality British thread guage to use to sort out and determine the thread size of a jumble of bolts? Auto supply stores hereabouts have American thread guages, but nothing for most of the bolts on my TR3.

Probably 99.44% of the nuts and bolts on a TR3 are SAE, as opposed to Whitworth or other British Standard, etc. The exceptions are, I believe, mostly with little screws and such found in some Lucas components and in the SU carbs. (Someone will correct me if I'm wrong or add to the list! :wink: )

 

[martx-5]

Re: Need Help with a "THREAD SIZE" for a TR3:

Does anyone know where to find a good quality British thread guage to use to sort out and determine the thread size of a jumble of bolts? Auto supply stores hereabouts have American thread guages, but nothing for most of the bolts on my TR3.

I'd say about 90% of all of the threads that I ran into on my TR3 restoration could be measured with a standard "American" thread gauge that has enough leaves to handle all of the common coarse and fine threads.

Sizes <span style="font-style: italic"><span style="font-weight: bold">smaller then 1/4"</span></span> on the TR3 are very likely to be British Association (BA) threads. I haven't run across a thread gauge for BA threads, but the only two BA threads I found in the TR3 were 2BA and 4BA. I just bought a couple of taps and dies in those sizes, and use the taps as thread gauges if I think they are BA screws. There may be some other BA screw sizes in the instruments, but I never measured them when I took them apart.

Edit: Be especially careful of the 2BA size, as it measures 0.185" by 31.4 tpi...very close to a 10-32 screw in diamater and thread pitch. Also, if you look at the chart I linked to, you will see that the thread angle (47.5°) is way different then the 60° we normally see.

 

[Member 10617]

Re: Need Help with a "THREAD SIZE" for a TR3:

Many thanks. Indeed, I have found that many of the nuts and bolts are SAE rather than BA, but I assumed they might have been added later. It makes sense that if so many of these cars were made for the US market that SAE might have been used.

I'll be careful with sizes smaller than 1/4 inch.

 

[TR3driver]

Re: Need Help with a "THREAD SIZE" for a TR3:

This ain't a mud slingin' contest, not to be taken as such.

Oh, absolutely! Just a difference of opinion, no disrespect intended.

As Andy says, the vast majority of fasteners on a TR3 are SAE standard (mostly NF). There are a few smaller bolts that are BA, but not all of them. And there are a few fasteners that don't fall into either system, like the studs on the gauges (which appear to be an oddball metric thread).

There are some BS thread gauges available at
https://www.samstagsales.com/whitworth.htm
but I haven't found them to be necessary. Instead, I recommend a strong eye loupe
https://www.harborfreight.com/5-piece-loupe-set-98722.html
and calipers
https://www.harborfreight.com/6-inch-digital-caliper-47257.html

Those, plus a good SAE gauge set and a thread chart like
https://mdmetric.com/tech/tict.htm
(which I have printed out and pasted to the wall) will make it easy to determine what thread you have.

For example, if the calipers give a diameter of around .183 (actual threads always measure slightly smaller than the nominal diameter given in the charts) and your 32 tpi gauge is just slightly too fine, then you are probably looking at a 2BA bolt.

Another way to tell what threads are involved is to look up the part number in the factory parts catalog. If the factory part number begins with letters rather than numbers, then it is a 'standard' fastener (which doesn't necessarily mean it is SAE) and you can look up the thread size and pitch in the Triumph Standard Hardware Catalogue .

One other comment, in cases where the factory part number does not start with two letters, there is something special about that fastener, which may or may not be obvious. It might be a special alloy, or have a special (unthreaded) shank length, or an oddly shaped head. IMO it's best not to try to substitute such fasteners unless you are certain what is special and can find an equivalent fastener.

 

[TR3driver]

Re: Need Help with a "THREAD SIZE" for a TR3:

Indeed, I have found that many of the nuts and bolts are SAE rather than BA, but I assumed they might have been added later. It makes sense that if so many of these cars were made for the US market that SAE might have been used.

Not a matter of being designed for the US market, IMO. British Standard (ie BSW, BSF, BA, etc) were already obsolete at that time, but the UK had not yet gone metric. So they just used what was cheap and easy. Many of the components with SAE threads (like the engine) were designed back in the 40's with no intention (at the time) of exporting to the US.

It is an amusing irony though, that my American cars for the past 30 years have been mostly metric, while my British cars have used mostly American threads

 

[Andrew Mace]

Re: Need Help with a "THREAD SIZE" for a TR3:

It makes sense that if so many of these cars were made for the US market that SAE might have been used.

That is true, and it dates back to right after World War II, when Sir John Black of Standard pushed for the Standard Vanguard as a "world car"! (Someday, I'll find again where I read that!) It's understandable that smaller "proprietary" components (electrical, hydraulic, fuel system, gauges, etc.) might have had carry-over thread types, as their design and/or production methods may have dated from well before WWII, though. I think Standard-Triumph was a bit of a pioneer in this. MG / BMC in particular did continue to use lots of Whitworth, British Standard and British Association fittings even as they sought the same "Export or Die" sales as Standard-Triumph after the War.

 

[Roger]

Re: Need Help with a "THREAD SIZE" for a TR3:

Just to be a little bit anally correct, the threads used as standard by the British car industry after the BSF/BSW are most properly called UN (Unified) threads.
That they are, to all intents and purposes, the same as SAE isn't entirely coincidence. It was done, as I understood, to ease manufacturing on both sides of the Atlantic and to some extent at the behest of GM (Vauxhall / Bedford) and Ford. Certainly the major market for British cars was the USA; in the immediate post-war years it was almost impossible to buy a new car in GB, all being destined for export.

 

[toysrrus]

Re: Need Help with a "THREAD SIZE" for a TR3:

Howdy Folks,

"Thanx Again" for the interesting stuff on Thds. I did a "Body-Off" on a `58MGA & now `57TR3 & find the same results. Most (90%) are an "SAE" fine pitch.

With that said; I have another one for you folks:

The Large Dia. spreader bar in front of the engine that mounts onto ea. side of the Chassis has "3" mtg. points on ea. side. "2" are thru holes (No Problem There) & "1" has a Thd. in the Chassis.

"What is the size of that Thd"???

Thanx Again,

Russ

 

[toysrrus]

Re: Need Help with a "THREAD SIZE" for a TR3:

Up late Russ? I'm going to bed

Howdy DNK,

No; "Just woke Up"! My daily routine (aka Habit) is this:

I`ll turn the "Boob Tube" on say 8:00-9:00pm (Speed, Golf or Tennis Channel - Thats basically all I watch) & the next thing I know; Its about 3:00-4:00am! If I get "5hrs" of sound sleep a day; I`m good to go.

This works out great for me cause; My home is my Office & I get all my Bus. emails, BCF stuff & whatever done by 8:00am! Then I have the entire day to go play in the garage with the TR3.

Russ

 

[TR3driver]

Re: Need Help with a "THREAD SIZE" for a TR3:

The Large Dia. spreader bar in front of the engine that mounts onto ea. side of the Chassis has "3" mtg. points on ea. side. "2" are thru holes (No Problem There) & "1" has a Thd. in the Chassis.

"What is the size of that Thd"???

All 6 of those bolts are P/N HB0906, which is 3/8" NF by 3/4" long.