I've been told there are two types with the same part number......one tapered and one straight thread with the same part number! Make sure you get the correct one for sure!
Holy crap, that is some serious info!2. from *during* the '69 season 'til the end of Harris Bonneville production ('85?), the original thread was 1/8"NPS (American National Pipe Straight; i.e. 'parallel') (note: being a pipe thread, the 1/8" refers to a nominal internal diameter - the o.d. is roughly 3/8");
3. however, for a short period at the beginning of the '69 season, some engines had 1/8"NPT (National Pipe Taper). The only documentation I've seen on this refers to the the T150 engine up to number AC01629; however, I've an early '69 T100R in my garage with a 1/8"NPT thread.
But (and it's a J-Lo ) ...
... we're talking about engines that are at least over 20 years old and could be twice that, with all that implies in the way of d.p.o. Both 1/8"NPS and NPT are 27tpi whereas 1/8"BSP is 28tpi and, as I've mentioned above, 3/8"Cycle is 26tpi (not to mention M10 x 1.0 is 25.4tpi ).
From experience, I would say extract whatever's screwed into the o.p. hole of your specific engine and check the thread *very* carefully with both thread gauges and a micrometer (ime, any taper is actually quite difficult to detect by eye ). In this, ensure you actually have a 27tpi thread gauge - don't try and interpolate between the 26tpi and 28tpi ones because it's very difficult to do, even under a magnifying glass.
Finally, btw, be aware that there isn't any such thread as BSPP (BSP Parallel) (or BSPS - BSP Straight) - 'BSP' is parallel/straight by implication, a tapered BSP thread is denoted 'BSPT'.
I'm pretty sure this is by Mr Healy, which I copied a while back, hope this helps.
It sure would be possible these old threads have been altered to suit whatever fitting was at hand.
Dragon, that first listing has some good info. Looks like it doesn't matter tooooo much to mix different standards as long as the pitch is correct and thread sealants are used. I used a tiny amount of high temp permatex sealant on the last few threads of the fitting. Def. don't want to get that in the oil flow.As I've always understood it, British pipe thread is 'parallel" not tapered like "our" pipe fittings. That's why Autozone oil guage fittings split Triumph timing covers.
Research it - http://www.google.com/search?source...ad+vs+american+pipe+thread&btnG=Google+Search
Yes, it's oil filled. The adapter used is a BSPT to NPT fitting which is the only thing I've found that actually screws in nicely without abnormal resistance.Not here to knock you mate but if I were to have a knob like that (is it oil filled) which is a taper in a straight thread it would be safe to have it supported at the other end knowing how the trump vibrates.
Thank you!E9526- 70-9526- Blanking Plug