I screwed up a couple of threads in my cylinder head where the inlet manifolds screw into the head (72' T120 Bonneville). Where might I get the correct tap to clear those threads out so I can get the new inlet manifold to screw in? Also, what is the correct tap for this thread?
Originally posted by Vox Teardrop: 5/16? This thread is over an inch in diameter.
According to the '72 parts book, there are 'early' heads and 'late' heads.
'Late' heads mount the carbs. to the head with 5/16"-dia. studs that screw into the head at one end, pass through the manifold (effectively just a spacer) and the carb. flange and take a nut on the other end.
Otoh, 'early' heads take manifolds with an external thread that screw into the inlet ports of the head.
Vox: Those manifolds have a locknut (S1932) each. If you don't have thread gauges (I'll presume you have a decent steel ruler to measure the i.d. of the locknut ), can you not take one with you to the tool supplier to help you locate the correct tap? I'll be very surprised if it isn't either Cycle or UNF (or possibly UNEF).
Re: Need a tap - inlet carb manifolds #119720 07/16/075:26 pm07/16/075:26 pm
Could even be a gas fitting thread BGT, best measure the TPI and diameter. Theres a toolshop near me that has lots taps for obscure/obsolete threads, if you can identify the thread, let me know. Close up foto?
Gas thread is 40TPI, it was phased out in the 40's but there is still some legacy stuff about (the threads on light fittings for lampshade holder is BGT in the UK)
99% of carb problems are electrical.
BMW R1150 Oilhead
Re: Need a tap - inlet carb manifolds #119723 07/16/0710:52 pm07/16/0710:52 pm
I buy all my strange size taps from Bass Tool in Houston. This one is a UNEF (united national extra fine) and Bass tool has the tap for $45.86 (actually not a bad price for a tap that big). Their website is www.basstool.com and the link for the page is http://www.basstool.com/PDF/Binder5.pdf. You can also just call them up. Their phone # is 1-800-442-0042. I can't verify the size but according to their catalog their P/N for a 1 3/8 - 16 is 372460 (but verify the P/N). They are good folks to deal with and I have bought a number of large UNEF's from them but unfortunately not that big or I'd loan it to you.
Re: Need a tap - inlet carb manifolds #119725 07/17/072:09 am07/17/072:09 am
Originally posted by drp: This one is a UNEF (united national extra fine)
I hate to rain on the parade but, no, it isn't - 1-3/8"UNEF is 18tpi.
Unfortunately, despite many goes with Google, what I can't find is anything showing large Cycle threads (although the part numbers changed between '68 and '69, which suggests it might not be Cycle anyway? ). However, I can confirm the thread isn't BSP, NPT or NPS.
Re: Need a tap - inlet carb manifolds #119728 07/17/076:02 am07/17/076:02 am
I think Brownowl may be right re the thread file, it is a bloody big thread for not much load and a little low strength Loctite would ensure a seal.
If you had a spare stub maybe slot that across the threads [like a tap] warm the head and freeze the stub and see if you can [very gently] run the stub/tap in and wait for temps to equalise before running it back out, be really carefull to de-burr the "tap" of course.
1969 TR6R 7.62 x 51 is not a maths puzzle.
Re: Need a tap - inlet carb manifolds #119729 07/17/071:39 pm07/17/071:39 pm
If you are unsure you could try running the lock nut onto the tap. It may fit a little tight but it should be obvious if it isn't the right size. Be careful when you start the tap, big taps can be difficult and will take some fiddling. I'd initially start it by hand and spare the wrench. Tools are like british motorcycles ...if you have the room you can never have too many.