Oil Plug Thread Difference 1968 T100S

[Cosmic Sled]

Three oil plugs with same thread, primary filler, clutch adjuster, and gearbox filler. 57-2166, T2166, E732, 70-0732 are the part numbers (all can be bought as the same thing). The threads on any replacement I have bought seem identical but they don't fit. I am down to the last of my original plugs. Does anyone know what the thread size is? With some threaded parts there is a choice given eg between BSF, UNC or cycle, but I can't find any reference to differences in these oil plugs. My engine number H61785, does anyone else have a problem getting the right oil plugs?

 

[rodsridin]

I had similar problems and ended up having to buy a set of thread gauges to finally match up. Here is a link to a description of various thread pitch and profile I found useful in my search:
https://threadingtoolsguide.com/en/blog/the-13-most-important-thread-types-you-should-know/

 

[Rudie]

anyone know what the thread size is?

1" Unified 16 tpi Constant Pitch (aka just "UN").

threads on any replacement I have bought seem identical but they don't fit.

The threads are almost certainly part of the casting, rather than being cut or rolled after casting. If so, probably the mould is slightly oversize (26 mm. o.d.?).

57-2166, T2166, E732, 70-0732 are the part numbers (all can be bought as the same thing).

Not all the same, earlier specifically filler plugs should have a small vent hole under the top edge of the cap; otoh, you do not want a hole in the clutch adjuster plug ...

down to the last of my original plugs.

If you are losing them, lockwire them or stick a piece of gaffer tape over them.

 

[Cosmic Sled]

Still searching for correct threaded plugs. Thanks for suggestions, I guess my bike uses Whitworth for this. The size is 7/8" and threads match up so it is the wrong flank angle? Anyway, a mate is planning to call around to measure for me, I will let you know if we findout. In the meantime, I have repaired one plug with correct thread but mashed up top by using epoxy type filler, photo to follow.

 

[Rudie]

You are posting misleading information.

I guess my bike uses Whitworth for this. The size is 7/8" and threads match up

Why would you need to guess? All threadform tables are available online with an internet browser search.

Then what do you mean by "match up"? If the 16 tpi I posted earlier, the threadform is still Unified Constant Pitch; it cannot be British Standard Whitworth as that is 9 tpi at 7/8" o.d. (BSW thread table).

57-2166, T2166, E732, 70-0732 are the part numbers (all can be bought as the same thing).

If your bike's plugs threads are only 7/8" o.d., the numbers cannot be for the same thing, T2166/57-2166 is the 1" Unified 16 tpi Constant Pitch I posted for you earlier.

a mate is planning to call around to measure for me

Owning an old British bike, I am amazed if you do not have a steel ruler and a set of screwpitch gauges already? Although if not, one of the cheap digital vernier calipers that appear in Lidl and Aldi from time to time is better for measuring larger diameters than any steel ruler.

 

[Cosmic Sled]

Thanks for all that info. I am always learning more and having to get creative. I have so far done a decent job of getting this bike back in use.

 

[Cosmic Sled]

I have attached a photo, the correct thread is on the plug on the right, all others are replacements that will not screw in.

 

[Rudie]

photo, the correct thread is on the plug on the right, all others are replacements that will not screw in.

All except the plug on the right have three full threads; if the threaded length is approximately 1/4", the thread on these plugs is most likely the Unified 16 tpi Constant Pitch I have posted for you already.

the correct thread is on the plug on the right

my bike
The size is 7/8"

While the tape measure in your photo is only useful for relative comparisons, unless your camera has a very weird lens, it shows the thread of that plug is at least a similar o.d. to the other three; therefore it is unlikely to be 7/8" o.d. when standard plugs are 1".

Your photo appears to show the threaded length of that plug is about the same 1/4" as the other three but it appears to have four full threads compared to the others' three. This appears to indicate a finer (more tpi) thread, perhaps 20 tpi that is coarser of the two Cycle threads at large o.d.?

 

[Cosmic Sled]

This is what we found. A Whitworth thread gauge marked 1.75 seems to fit the original (the plug on the right in my picture, which screws in) and the replacements (which bind when screwed in about half a turn). The o.d. of the original we measured as 24.02 and the replacements as 25.04

 

[Rudie]

The o.d. of the original we measured as 24.02 and the replacements as 25.04

I.e. 1" nominal, not 7/8" ...

A Whitworth thread gauge marked 1.75

<sigh> There is no such thread gauge; gauges to measure any Imperial thread are marked only in whole numbers.

Your friend was using a set of thread gauges with "WHITWORTH" on one side and "METRIC" on the other? If so, 1.75 is a metric pitch (distance between adjacent peaks or troughs), equates to approximately 14 tpi.

1" diameter and 14 tpi is not a Whitworth thread, 1"BSW is 8 tpi (1"BSF is 10 tpi).

Otoh, 1" diameter and 14 tpi is a UNS (Unified Special) thread; however, if it really is 14 tpi and not your/your friend's inaccurate measuring, a distinct possibility is a previous owner of your bike made the plugs and threads; this might also account for the different head shape of the plug that fits.

Imho, E732/70-0732 and T2166/57-2166 currently sold with the same thread warrants further investigation - E732 dates back at least to the first 21 in 57, unlikely ime Triumph would use a Unified threadform then, 69 on give a different part number to (allegedly) exactly the same part?

 

[Cosmic Sled]

Yes exactly regarding part numbers. Anyway problem solved, I think you said this in your first post, the thread is the same, just oversized. I have been able to reduce one replacement so it screws in. I now have all three plugs fitted.

 

[Cosmic Sled]

Thanks to all for contributing Happy riding!