Exhaust Roses

Have you installed the round gasket that goes inside the head spigot prior to installing the pipe in the spigot? Sorry if I have asked the obvious.

There are 3 original variants of NHT roses. All NHT ports are 3/4" deep. The first 2 are for full depth flange mount pipes that also use, as mentioned,  the port bottom gasket. These first 2 type roses have a clear cut 1/8" before the threads start and may be why your roses don't seat fully in a bare port. Are they aftermarket? The pix does not show whether chamfer or a clear cut lead in. The first rose is for 1949 thru 1972. The second is almost identical except for the big fins for 1973 750 only. The 850 ports are 3/4" deep but the 850 style pipes fitting dictated the changed later 3rd big fin rose depth dimension. Prior port thread damage from loose pipes can contribute to roses not seating fully unless threads are chased with a clean up tap..

http://atlanticgreen.com/nhth.htm

Slightly off track here, but you are permitted to laugh.

As an ignorant young fool in my yoof (as opposed to an ignorant old man in my dotage) I owned a string of Tiger Cubs. Actually looking back I think they were held together with string- but I digress even further. Being a Tr****h, there was a short stub, held in the head by very fine threads, to which the actual exhaust pipe clamped. Having spent a Saturday afternoon messing about with different silencers, took the bike out for a good thrash, to hear the final results. Giving it a big handful, the stub blew out of the head and deposited the pipe on the road. Obviously nothing was tightened up properly. So I pulled over, and ran back to get the pipe, before it got mangled by any following traffic. In my haste, I picked up the pipe. Of course, I didnt bother with gloves.....

All together now.......

Since acquiring my  second Norton, a combat, in 1987, I have  on occasion been accumulating old norton parts at fleamarkets (autojumble). And In addition the occasional bike.

In 34 years I have now 24 nortons, some assembled but most basket cases. A supporting pile of NHT parts and bikes from 1949 through MK3 e-starts. I sell nothing...It is held 95% for research assets. My pre-Berlinner inventory is incomplete. I look at the parts books, I scrutinize the parts to detect any changes large or small. On occasion I write some things down and have a very full file cabinet drawer of all kinds of documentation. As a career long master technician (& 6 years of college) I professionally was required to investigate mechanical as well as electronic faults on multimillion dollar government and other industrial equipment. 

Doing NHT was just a hobby for my own interest. In 1970 my first new norton roadster was a disaster and after 17 years I wanted to try again.

Only had 5 Nortons. There are roses with different thread lengths. The short stroke Manx and maybe some other singles have a longer thread rose. Guess due to the large head finning that makes it hard to tighten. Had to grind off a large portion of a standard tool to make it possible to to tighten the rose without breaking any fin.

left t 1949-72 

center 73-750 big fin

right 850 shorter thread & big fin 

The final 1/8" or thereabouts of the outside diameter of your new ones looks to be bigger than the old one.  Maybe the tip is jamming before they are screwed fully home.  That seems to be the only possible reason why they won't go far enough in to squeeze the swaged flanges on the pipes against the copper washers.  The threads are parallel not tapered, so the only other possibility is if the thread pitches are a bit different.  Can you put the new and old ones side by side facing opposite each other to see if the threads interlock and match each other?  If so, you could turn a little off the outside end edges so they will enter further.  The inner edges bear against the pipe flanges so you can safely lose some off the outsides.

The issue might be an incorrectly toleranced part or something to do with an earlier thread repair. 

Our Atlas has s similar issue. A bit complicated by the early big bore pipes with the Manxman type complex bends  that grip the rose nuts and also  damage to the innermost  port threads  from the pipe flange bouncing around when loose. We have managed it with a couple of copper washers in each port.  A thread chaser would help or as David suggests, try  file off a few mm of thread from the nose of the nuts. There is a collet  fitting that may help, a Commando part?.

I have seen all sort of NHT heads in various degrees of abuse damage, I have repaired several dozen heads with new welded in inserts and cleaned up several with an H6 class tap almost $200. On ocasion I have cold formed extruded the threads back with ultra cleaned head and  rose nuts and our STP as the  coldl forming lube.

Cutting metal away is an absolute last resort. for me.  I refuse to mess up a head with bad  pipes and they will go in the trash can before I sacrifice the head. Good useable down draft small bolt pattern heads (S650/136) heads are incredibly rare here in the US. I feel lucky to have 2 usable ones.

We aren't suggesting to cut the head...just taper off the outer tip edges of the rose nuts...

Its funny, I have had a brand new  old stock  Dommy rose nut  with  intact  satin chrome  finish and those nice gently  rounded ears ,no ugly  clumsy  block ear ,sitting on my  office desk for 20 years .  Never managed to find  another gen one to make a pair.  Its nuts  ,it  really  is.

I've been retired for a few years now , but while working I had been temporarily assigned to the calibration shop (electronics and mechanical) .I had performed a series of 3 wire thread measurements on a big portion of all the NHT roses I owned. The big take away was, the folks that measure the outside diameter of the threaded rose, fail to understand the actual thread engagement size is not the thread OD but is the "pitch diameter".

The pitch diameter measurements varied as much as the thread OD measurements and exposed the reason  for such variations of rose to head tight or loose fit relationship. I had measured likely OEM as well as roses of unknown origin, I assume both aftermarket as well as custom made.

This research has been offered, occasionally,  at my tech session presentations.

I would like to clean up the Atlas  port thread ,what size is it? .I guess I would need a bottom tap.

Hi Robert, exactly what I did on my rebuild, the head had stood for 48 years with the roses screwed in so after weeks of soaking with all sorts of anti corrosion fluids I eventually got them unscrewed. Luckily I had a pair of Identical roses so I milled off the thread ‘lead in’ then machines longitudinal ‘L’ shaped grooves to form a crude tap. This I used to clean out all the gunge from the head and by gentle persuasion managed to extend the thread as if it were a plug tap. Only worked because it was into aluminium.

Regards

Dick

It would be handy to know as they need to have a plain end lead-in as people have said.  Yours seem to have a tapered end, which clearly isn't so good.  A-N don 't show the thread end but RGM does and they also produce a leaflet to cover the many types of roses (but NOT Cadbury's!)

I attach it here.  Notice the recommended cleaning of the exhaust ports.

I would still like to know what the thread is,  anyone ?.

CYLINDER HEAD  -  ALLOY

Part                                             Part No        Threads           Length         Notes  (alt p/n)

Banjo bolt, rocker oil feed           18101           5/16" x 22             7/8"             BSF    067696

Bolt, Cylinder head fixing, long.  T2096           3/8" x 26             2 1/4"     all 500, 600, 650   060401

Bolt, Cylinder' head fixing, centre, short  T2097  3/8" x 26        1 1/4"        25313, 067918  

Bolt, Cylinder' head fixing,  long  24253          5/16" x 26           2 1/4"        750 Atlas & Hybrids

***Exhaust Port – Threads***      18092        1  15/16" x 14                         D12/167

I agree with Lionel,

Looking at the pictures, you appear to have run out of thread towards the Rose.

Therefore no surprise they don't tighten up.

For my last twin restoration, a 1960   99,  I bought the RGM version and special tool with no issues.

You could always find an engineer to add some more threads, sizes provided by Phil, above.

Thanks Phil.  I am presuming  thats BSF ?,    Going to be fun finding one of those taps.

Robert........good question.  I don't know the answer. For years the size and thread was often posted as 1 1/4" x 14tpi. I always assumed the threads to be CEI or BSF. Perhaps Dave Comeau knows???

When my first 650SS head lost both of its exhaust threads I took it to a London engineering company called BLR who tapped the ports one size up and supplied oversize brass nuts to fit. 

These worked absolutely fine for the next 40 plus years. I needed to find slightly larger exhaust washers which was quite easy. I never ever had loose exhaust roses again.

1-15/16x14tpi is the tap I use which is the only thing available here in the USA. It works perfectly in original heads and does not scrape an metal away only the carbon and dirt. I also use it to chase the threads on welded in inserts to make them "perfect". A wire brush cleaned and lightly, oiled  rose spins in slick as can be,and is not sloppy. My tap IS 60 degrees class GH4. I have no ability to test ports for CEI or 55 degree BS. I could never understand the 1.997" x 14tpi listed in the shop tech data? Only unverified rumor that it was some railroad or steam engine fitting thread.

Even better than all that, 1-15/16x14tpi  it is what is printed on the factory 650SS head drawing!