• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

What thread pitch to use

Share this page

M

Member 10617

Guest
Guest
Offline
When I undertook to remove my oil pan, I was advised by some forum members that all the bolts holding the pan, regardless of length, are 18 threads per inch. This was very helpful to know up front, although I would have discovered this if I had tried to insert new bolts of another thread pitch. Your guidance saved me some frustration.

My question is this: Do any of the manuals indicate what thread pitch is required on different components of the Triumph? I haven't found such a listing or chart. Or do you simply have to inspect a bolt when you remove it to determine what thread pitch it is and hope that the previous "mechanic" inserted the right bolt and didn't jam in an incorrect one.

With a car that has had at least three or possibly four previous owners, one never knows.
 
There are several sources of thread pitch information; unfortunately none of them are complete. For part numbers that begin with two letters (eg HU0855), there is a "magic decoder ring" at
https://docs.google.com/viewer?a=v&p...1Y2M4&hl=en

There are also some thread pitches given in the fastener torque table in the front of the workshop manual, eg "sump attachment" P/N 100749 is given as 5/16-18 NC Setscrew.

And sometimes you can glean the information by supplier cross-references. For example, TRF supplies HU856 in place of 100749, which the standard hardware catalog gives as 5/16 UNC.

And of course you can always ask here!
 
Randall and Tom,

Many thanks for the information. The link to the hardware catalogue is especially helpfuland interesting. I have saved it and will refer to it when I have a question. And the information there gives me a key to references in the Service Manual.

Great material.

Again... many thanks.
 
if you get a tap and die set, it comes with a thread gauge, very helpful for figuring out the threads per inch on a bolt.

Hondo
 
Hondo,

Now there's a good thought. In the meanwhile, I have ordered a US and a metric thread guage from Bolt Depot. They are small plastic cards with a series of thread guages (very inexpensive).
 
I would suggest adding a magnifying lens of some sort (HF sells a nice set of loupes for cheap) and digital calipers. There are a few fasteners on a TR3 that are neither metric nor SAE (US) threads; and it can be tricky to tell the difference between, for example, a 10-32 thread (32 tpi, major diameter .190") and a 2 BA thread (31.75 tpi, major diameter .185"). Adding to the complication, "major diameter" is a theoretical measurement, the actual bolts will always measure somewhat smaller.

Standard-Triumph seems to have used only SAE threads, but their suppliers (Smiths/Jaeger, Lucas, SU, etc) mostly used British threads.
 
Second the magnifier.
Lately been having trouble with the little ones!
Like the plate screws on a #22 Dizzy
 
Absolutely.... a magnifier is a must. I have some the jewelers use. My hope is that I will be able to reuse any bolts that I remove (temporarily) from the car, so I won't have to struggle to find replacements, but that is not always possible.
 
LexTR3 said:
so I won't have to struggle to find replacements, but that is not always possible.
Click to expand...
FWIW, Moss & TRF have 99% or better coverage for 'correct' bolts. Sometimes it's worth paying their prices (which admittedly are rather high) to be sure you've got the right bolt. There is a whole lot more to bolts than just thread size!

For example, in many cases, the factory used bolts in 1/4" or even 1/8" length increments, rather then the 1/2" increments generally found at the hardware store. There are also cases where the shank length or diameter is important, plus sometimes bolts that are specially hardened, etc.

My rule of thumb is that if the factory gave the bolt (or nut, washer etc.) a special part number (5 or 6 digits rather than 2 letters) then there is something special about the bolt.

Just one example, the front center bolt on the oil pan has to be just the right length (and have the right thickness of washers) to get full strength in the aluminum threads, without bottoming in the hole (and not clamping the pan correctly). IMO it's well worth paying TRF $.80 for a single bolt, just to be sure it's the right one.
 
TR3driver said:
Standard-Triumph seems to have used only SAE threads, but their suppliers (Smiths/Jaeger, Lucas, SU, etc) mostly used British threads.
Click to expand...
By the time the TR3 was out, that's pretty much the order of things. Lucky me, the TR2 is almost completely British Standard.... :rolleyes: Except the engine and tranny... Kinda like a backwards mid 80s Chevy..
 
Randall,

Good advice. For the pan bolts, I got one set from Moss (they supply only the ones for the 16 bolt holes), and a full set (including the so-called odd-ball ones) from TRF (some were on back-order for quite some time), and then a complete set of all the bolts from the Bolt Depot. Also, I got my washers from Moss and TRF and Bolt Depot. So, comparing all of them to make sure they were exactly the same for the various sizes, I chose the best ones and used them on the pan.

Knowing little about all this (just enough to get into trouble), I always order bolts and other fasteners from Moss or TRF (even cotter pins and washers!) rather than find them at the local hardware store or auto parts store. I, too, figure that Moss and TRF must have a reason for distinguishing among the items.

My exception, is that I ordered some from the Bolt Depot (because they have such high quality bolts), but made sure they were EXACTLY like the ones from Moss and TRF. Easy to do when there right there in my hand.

I'd rather spend .80 on a bolt from Moss or TRF than .40 on a bolt from local hardware store and find that I have used the wrong fastener.
 
Banjo said:
By the time the TR3 was out, that's pretty much the order of things. Lucky me, the TR2 is almost completely British Standard.... :rolleyes: Except the engine and tranny... Kinda like a backwards mid 80s Chevy..
Click to expand...
Interesting. I've not seen any change points in the SPC that would reflect that ... do you have some examples? Is your TR2 body sewn together with BS bolts?
 
TR3driver said:
Banjo said:
By the time the TR3 was out, that's pretty much the order of things. Lucky me, the TR2 is almost completely British Standard.... :rolleyes: Except the engine and tranny... Kinda like a backwards mid 80s Chevy..
Click to expand...
Interesting. I've not seen any change points in the SPC that would reflect that ... do you have some examples? Is your TR2 body sewn together with BS bolts?
Click to expand...
Fenders for one. All the bolts are BS. Fortunately I have a good set of Whitworth wrenches and sockets, cause neither my standard, or metric wrenches fit anything on the body of car real well.
I'll double check some threads, just in case I'm mistaken. I will try and give you some pics within a day or so.
 
Seems like something must be wrong there. As you can see below, the front fenders are all supposed to be HU07xx bolts, which are 1/4-28. The rear fenders have some special bolts (with low profile 'button' heads), but are still 1/4-28 threads.

Maybe the heads have rusted until a 7/16" AF wrench is no longer a snug fit? I ran across some of those while robbing the grill surround from the rusty hulk in Dad's shed. Having the front apron installed with Bondo (rather than bolts) didn't help either!
 

Attachments

  • 26239.jpg
    26239.jpg
    26.6 KB · Views: 222
TR3driver said:
Just one example, the front center bolt on the oil pan has to be just the right length (and have the right thickness of washers) to get full strength in the aluminum threads, without bottoming in the hole (and not clamping the pan correctly). IMO it's well worth paying TRF $.80 for a single bolt, just to be sure it's the right one.
Click to expand...

That's a perfect example. When I took my engine apart, I marked that center bolt with yellow paint and screwed it back in to the sealing block so I wouldn't lose it.

I sometimes find myself picking through the "old stuff" looking for that odd 1/8" or 1/4" increment fastener when putting things back together. Good enough reason to not through the old stuff out.
 
TR3driver said:
Seems like something must be wrong there. As you can see below, the front fenders are all supposed to be HU07xx bolts, which are 1/4-28. The rear fenders have some special bolts (with low profile 'button' heads), but are still 1/4-28 threads.

Maybe the heads have rusted until a 7/16" AF wrench is no longer a snug fit? I ran across some of those while robbing the grill surround from the rusty hulk in Dad's shed. Having the front apron installed with Bondo (rather than bolts) didn't help either!
Click to expand...
I bow to thee, Oh Randall :bow: hehehehe
I just got down to the "nuts and bolts" of checking out the nuts and bolts of the TR2. Not sure where I got led astray, but according to my thread pitch gauge, all the body hardware is either 1/4 20 or 1/4 28. It does seem that my 1/4 whitwoth wrench still fits the heads better than the 7/16 SAE, and still not as snug as an 11MM. go figure.
Rust is not the culprit. most of my fasteners are clean, and a major reason I picked this project is it's distinct lack of rust.
The bottom line is ,following your information, my world just became a TON easier.
Thanks for planting the seed of doubt in my mind with the Truth. hehehe
The front fenders on mine are held on with 1/4 20s tho, not 1/4 28. But it is possible someone changed out all the captured nuts in the front end. it's been hit in the front. The rear are 1/4 28, the button head ones are the ones you can see on the inside of the seam when you open the trunk lid.
 
As a point of interest, a 7/16" UN wrench (SAE if you like, but not strictly so) is exactly the same size as 1/4" BSF or 3/16" BSW! So if you find that one fits better than another, it's due to manufacturing discrepancies, or wear and tear, in the wrench.
 
That's curious, as my information shows that a 1/4" BSF bolt should be 0.445" across the flats, while 7/16" is 0.4375". Close, but not exact.
 
You are right, I wil now humbly grovel. Don't know what I was thinking of.

I read this misinformation recently and it drove 60 years of knowledge straight out of my head.
 
Back
Top