Thread type question

[robs ss]

What is there thread type for the three studs into the underside of the head?
I know it is 3/8" 16TPI - but is it UNC or Whitworth? (EDIT: sorry - I was wrong here - 20TPI)
Cheers

 

[L.A.B.]

It should be 3/8" - 20 BSF.

06-7885

Stud, 3/8" x 1-7/8" x 20-26, Cylinder Head ( Alt # NM24389 )

www.baxtercycle.com

"Stud, 3/8″ x 1-7/8″ x 20-26, Cylinder Head"

 

[Fast Eddie]

But it is common to use 3/8 UNC when using inserts.

 

[Ron L]

But it is common to use 3/8 UNC when using inserts.

Which means you must make/buy new hardened studs in 3/8-16 and 26 TPI on the nut side. Or make/buy new nuts.

 

[Fast Eddie]

Which means you must make/buy new hardened studs in 3/8-16 and 26 TPI on the nut side. Or make/buy new nuts.

Yes. But they are readily available, from JS and cNw.

 

[robs ss]

It should be 3/8" - 20 BSF.

06-7885

Stud, 3/8" x 1-7/8" x 20-26, Cylinder Head ( Alt # NM24389 )

www.baxtercycle.com

"Stud, 3/8″ x 1-7/8″ x 20-26, Cylinder Head"

Thanks for that Les - My friend is about to purchase a threadsert kit for his failing studs. The LH one below the exhaust port will only just accept 20 f/lb.
Is there any uncertainty that the stud thread that goes into the head is 3/8" BSF?
It is a Fullauto head installed by someone unknown.
Cheers

 

[kommando]

It is a Fullauto head installed by someone unknown.

Only way to be sure is to take the current stud out but that does not change the 3/8 UNC insert with matching stud being the best solution long term although its not factory fit.

 

[Fast Eddie]

cNw Head Mounting Kit

Type 3 5 ea ARP/cNw 12 point head bolts. 3/8 – 26 thread. ARP 300 series, heat-treated stainless that is rated at 180KSI (180,000 psi) The 5 bolts above are also cut down in the center or ‘waisted’ in order to accurately maintain a torque 3 ea ARP head studs. 3/8 – 16 x 3/8 – 24. ARP 8740...

coloradonortonworks.net

 

[L.A.B.]

Is there any uncertainty that the stud thread that goes into the head is 3/8" BSF?
It is a Fullauto head installed by someone unknown.

Is it 20 TPI?
According to Time Warp the Fullauto head thread is 20 TPI...:

Cylinder head helicoil thread

Hi Ladies & Gents, One of the 2 studs corresponding to numbers 7 and 8 of the tightening sequence is loose in my Combat type head because the thread in the head has been damaged. I plan to fix that by installing an Helicoil insert in the head, but I don't know the size and thread of the side...

www.accessnorton.com

The FA cylinder head has the same 20 TPI as stock, we will hope the new US based manufacturer of that head will change the TPI to 16/18 tpi and include three studs to suit.

Edit, CORRECTION:
...and, as far as I'm aware, the original head and stud upper threads are 55°, 3/8" - 20 BSF (the same part number studs used well before the Commando so unlikely to be 60°, 3/8" 20-UN). Edit: (Incorrect information deleted).

 

[robs ss]

Is it 20 TPI?
According to Time Warp the Fullauto head thread is 20 TPI...:

Cylinder head helicoil thread

Hi Ladies & Gents, One of the 2 studs corresponding to numbers 7 and 8 of the tightening sequence is loose in my Combat type head because the thread in the head has been damaged. I plan to fix that by installing an Helicoil insert in the head, but I don't know the size and thread of the side...

www.accessnorton.com

Edit, CORRECTION:
...and, as far as I'm aware, the original head and stud upper threads are 55°, 3/8" - 20 BSF (the same part number studs used well before the Commando so unlikely to be 60°, 3/8" 20-UN). Edit: (Incorrect information deleted).

Thanks Les - so we'll go with 3/8 BSF (not apart yet) and buy/make studs to fit if needed.
Lead time on Threadserts is such that we don't want his bike off the road for that long.
Cheers

 

[998cc]

Thanks Les - so we'll go with 3/8 BSF (not apart yet) and buy/make studs to fit if needed.
Lead time on Threadserts is such that we don't want his bike off the road for that long.
Cheers

Lead time getting British Helicoils was the issue a few years ago while putting my Vincent motor together. I threaded the case to take a 5/16" UNC Helicoil and made up a new custom stud with a 5/16" BSF outer thread. No worries at all.

 

[Time Warp]

Thanks Les - so we'll go with 3/8 BSF (not apart yet) and buy/make studs to fit if needed.
Lead time on Threadserts is such that we don't want his bike off the road for that long.
Cheers

As per the thread linked to, Jim Comstock did not recommend that. ( using a 20TPI Helicoil )
Post #12.

I had also noted the lack of thread engagement of the stock Commando stud, JC posted the stud had been longer on earlier models (Atlas perhaps)

I had posted long ago about my concerns of the 3/8-20 threads in the FA head and was told here by the maker there was no problem with those threads and was a trouble maker.
That same person some time later (iirc) posted having the threads inserted.

What I found was new 3/8-20 studs were a perfect fit in my Jim Comstock Al/Bronze inserts 750 head but those same studs in the FA head were a wobbly fit and was in no doubt they would pull out.
What I did in the end was make new studs from 750 head bolts, each 20 TPI thread had to be cut to suit each thread in the FA head and were full engagement in the head.
Each stud was longer externally also.
The difference compared to a stock stud in the picture.

Will it last, I hope so, if not I will use a 3/8 UNC helicoil.
It was also noted the FA head has less cooling area (fins) than a stock head.
Lets hope the current manufacturer did not do that also.

 

[Time Warp]

It might be worth noting, if a 3/8-20 coil insert fails (if a coil is the intention) then what, a Bigsert as the only repair ?

It might be also noted I did not go to the trouble of making tools adapters to torque the cylinder head to fill the day in.
Cranking on those fasteners on a FA with abandon will either pull the threads over time or the nuts/sleeve nuts will have loosened.

 

[CanukNortonNut]

Uni-Thread
Universal threading system
Thread Repair Kit
3/8X20 BSF are available from Waldridge Motors
I have installed them.
You can also go cNw: 3/8X16 if you want to use their studs / and nut system. I have installed this system. Good results.

"I'm not knocking or promoting products here", either system works, but options are available.
Both of my 850 heads needed the inserts due to stripped holes. I am doing my second one now. One failed but all three get the treatment.
IMHO, I would do it automatically if the head was "off the bike". Do it! But don't drill too deep.
These threaded hole are going to fail eventually. Bad design IMHO but that's what we got for an almost 50 year old machine. Nothing stops us from making things better. Right?

Comstock did a torque test to failure, on heli coils and other inserts.... you should check that out.
Why cry in the garage, after your third heat cycle torque up and it strips before torque up to spec. Or the front nut #7 or #8 will not get tight. Wonder why you got oil stains between the head and the cylinder and that damn nut will not tighten up but keeps spinning. Been there!
Cheers,
Tom

 

[Time Warp]

If the three holes were drilled all the way with a 3/8" drill you could use bolts and nuts.
You won't be pulling those out.

 

[gortnipper]

Thread inserts in the Norton head (2019)

Here I have tested 4 common inserts used in the Norton head. These inserts were all 1/2 inch long. They all fit a 3/8-16 stud.

www.accessnorton.com

 

[robs ss]

If the three holes were drilled all the way with a 3/8" drill you could use bolts and nuts.
You won't be pulling those out.

Two of them would go all the way into the exhaust ports - not really an optimal solution.

 

[robs ss]

It might be worth noting, if a 3/8-20 coil insert fails (if a coil is the intention) then what, a Bigsert as the only repair ?

It might be also noted I did not go to the trouble of making tools adapters to torque the cylinder head to fill the day in.
Cranking on those fasteners on a FA with abandon will either pull the threads over time or the nuts/sleeve nuts will have loosened.

View attachment 96711 View attachment 96712

Very nice!
Mine not quite so - but equally effective. If others are going this route, just remember to use them at right angles to your torque wrench or you will have to recalculate what the reduction in torque should be due to the extended length.
Cheers

 

[Chris Zet]

When you do this thread repair of this 3 critical studs i can warmly recommend Keenserts thread inserts with key locks for this job.
Had tried several types of inserts......best in my technical understanding and own experience are this Keenserts.
I only could buy M10 standart metric thread Keenserts here in Europe. Outside thread is M14 s.m.t. ...this is about 17tpi. sounds better for me for alloy cast than 20tpi. I ordered at my local machine shop 3 studs with M10 thread on one side that goes into the insert and 3/8" BSC for the nut side. Works great......good feel when you torque head down. Bulletproof.
BTW saw last december on a facebook post that John Snead, manufacturer of the Fullauto STS, also uses these Keenserts......

 

[TomU]

It might be worth noting, if a 3/8-20 coil insert fails (if a coil is the intention) then what, a Bigsert as the only repair ?

It might be also noted I did not go to the trouble of making tools adapters to torque the cylinder head to fill the day in.
Cranking on those fasteners on a FA with abandon will either pull the threads over time or the nuts/sleeve nuts will have loosened.

View attachment 96711 View attachment 96712

Here's a commercially available tool that does the same thing

Adjustable Torque Wrench Adapter - Motion Pro

Motion Pro - High quality cables, tools and controls for motorcycles, ATVs, snowmobiles and personal watercraft.

www.motionpro.com