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! Ok, so, I have no idea what I really have because the plug that came out looks stock, but didn't feel as if it fit correctly. It didn't leak, but it didn't really tighten. Felt stripped and very sloppy. So, I don't want to rely on that. What I have in there now is a Sunpro gauge adapter that is a BSPT to NPT. Very carefully and slowly, I gave it a go. It screwed right in and tightened up nicely. So, with that said, it might not be the correct threads, or I made new ones not by choice, but it's in and everything seems fine, tight, and not cracked. Who the fk knows at this point? I just want to ride the effin' thing instead of worrying about it all the time and dealing with one crazy abnormal situation after another. I've had the bike for about 2 months and have ridden it like 5 times. The rest of the time I've been dealing with carbs, stripped threads, valve adjustments (normal), and now a mystery thread issue on the timing cover.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