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Thread forms #781412 08/13/19 9:58 pm
Joined: May 2015
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Qual Offline OP
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Is there a list around that shows the various nuts bolts and thread forms for ‘53 B33 please?
Specifically what thread is the head holding down stud?
Thanks for any help
Dave

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Re: Thread forms [Re: Qual] #781414 08/13/19 10:23 pm
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Hi,
The head studs on a B33 are 3/8 x 26tpi (CEI) where they thread into the head
The stud lower ends rotates within a fitting that is screwed into the crankcase,
This does not need to be removed to dismantle the engine,
The threads into the crankcase are 11/16 x 20tpi
BSA seem to use 20tpi for all studs and bolts from 7/16in. upwards, for their pre unit models
The BSA Service sheets are available on https://www.bsa-oc.com/en/service-sheets-2/

Studs and bolts/nuts are listed by part number here stainlessbits.com/link12.html
A parts book is invaluable when working on old BSA models

John

Re: Thread forms [Re: chaterlea25] #781446 08/14/19 11:22 am
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Qual Offline OP
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Thanks very much John, most helpful.
Is 3/8” 26tpi CEI similar to BSF thread form? I have taps and dies for BSF.
Dave

Re: Thread forms [Re: Qual] #781448 08/14/19 12:07 pm
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VicCyclone Offline
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BSF is a Whitworth thread form as is BSCy otherwise known as CEI but has a 55 degree angle rather than 60 degree. The only thread that is effectively interchangeable is 1/4 BSF and 1/4 BSCy. The shank and hex sizes are the same but the threads per inch are very different. Other than 1/4" they are not interchangeable and you should not put your other BSF taps and dies anywhere near Cycle Threads especially on the engine, gearbox or frame castings. You can of course use paired BSF fasteners on cycle parts - they are a lot cheaper, but the reason BSCy was used in the first place is that the finer threads are more resistant to vibration than their coarser BSF counterparts.


VicCyclone

1965 A50 Cyclone Clubman
1966 Victor GP
1967 Victor Special
1968 Victor Special
1968 A65L

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Re: Thread forms [Re: Qual] #781449 08/14/19 12:08 pm
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Ginge Offline
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No. CEI is different to BSF. Early Brit bikes use British Standard Cycle/CEI thread form in some components. Whitworth/BSW thread form in other components, especially studs into alloy housings.

26 threads per inch, and 20 threads per inch are common on ‘50’s bikes. Both are CEI thread forms on old Brit bikes. Neither matches anything available in an off the shelf modern tap/die set.

You need to get an individual CEI tap from an engineering supplier or reputable Brit bike supplier. Especially if you are tapping head bolt studs.


'51 C11 in a '54 C10L frame..."The Bantam Eater"
'70 Triumph Trophy 500. Bottom end rumble awaiting diagnosis
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Re: Thread forms [Re: Qual] #781451 08/14/19 12:35 pm
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Qual Offline OP
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Thanks chaps
I’ve got new cylinder head through bolts which are very tight in the head and I thought I’d chase them down.
Any views or else I’ll get the appropriate die to try and relieve them a tad.
Dave

Re: Thread forms [Re: Qual] #781452 08/14/19 12:55 pm
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Ginge Offline
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To expand on Vic’s post;

Whitworth is a coarse thread. Generally used for studs into alloy castings. 55 degree pitch. TPI varies with diameter but it remains a coarse thread. Think industrial revolution style machines that vibrate, emerging alloy technology, big coarse threads to hold everything together.

CEI is a 60 degree thread form. Less coarse than Whitworth. The TPI varies with diameter. In Britbike world 26 TPI is about as fine as we go. This thread form originated with bicycles. Think big diameter, steering head, pedal hubs and bearings, axles and ball bearing cones. A good strong engineers thread capable of gripping with minimal thread catch.

BSF/UNF also has a 60 degree pitch and is a fine thread with TPI decreasing as diameter increases. As Vic says, it crosses over CEI at 1/4” but they are not the same pitch. Sometimes it works. Sometimes not. BSF/UNF was an attempt to standardise engineering across the known world until metric fine/coarse became the norm ( except in the USA)


'51 C11 in a '54 C10L frame..."The Bantam Eater"
'70 Triumph Trophy 500. Bottom end rumble awaiting diagnosis
'72 Triumph Tiger 650. Back on the road...
Re: Thread forms [Re: Qual] #781483 08/14/19 10:47 pm
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chaterlea25 Offline
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Hi Dave,
I have found that the threads in the cast iron head get a coat of rust so the bolts go tight
Look up, https://www.tracytools.com where you can buy a 3/8 x 26 tap and die to sort out the threads
There are lots more 3/8 bolts and nuts on the BSA that will need attention
(buy a 5/16 x26 tap and die too)

John

Re: Thread forms [Re: Qual] #781560 08/15/19 6:21 pm
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Nick H Offline
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I'm also investing in taps and helicoil kits and wondering if BSF 3/8 x 20 and 5/16 x 22 might be more generally useful for BSA and Triumphs. I think these are the coarser threads of some studs and are more likely to be stripped out of the case itself.
Can anyone back up this idea or suggest their most useful thread repair kits?


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Re: Thread forms [Re: Qual] #781643 08/16/19 2:06 pm
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Qual Offline OP
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Thanks for all the useful responses, I now know the way to go.

Now, another problem, I’ve just removed the mag pinion to find that there is excessive play in the mag bearing.
Assuming now that a complete overhaul is probably required.

Does anyone have any suggestions of a good repair shop please?

I think with this project everything I look at is going to be an issue!
It was a one-owner family transport lugging a double adult chair around!
Cheers
Dave

Re: Thread forms [Re: Qual] #781660 08/16/19 5:41 pm
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George Kaplan Offline
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Originally Posted by Qual
Does anyone have any suggestions of a good repair shop please?
Dave

Read this thread:

http://www.britbike.com/forums/ubbt...g-a-rotating-armature-magneto#Post446733
And I mean all of it.

Then choose a repair shop.

I am not certain if anyone on here recommends mag repair people but the thread above will arm you with enough tips to weed out some of the cowboys.

John

Re: Thread forms [Re: Qual] #781712 08/17/19 9:29 am
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Qual Offline OP
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Thanks John

What an interesting link you sent. Was still reading it last night at midnight!

It just reinforced my view that I’m not equipped to tinker through lack of knowledge, engineering facilities and time!

I’d thought if one of the new bth mags but £800 is way too much.

Incidentally, a recommendation for Tracey Tools, I ordered taps and dies yesterday and they’ve just been delivered! Can’t get better than that!
Dave

Re: Thread forms [Re: Qual] #781720 08/17/19 12:03 pm
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George Kaplan Offline
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Hi Qual, I have just realised that you are in the UK so I tried to PM you but I got a message saying that you don't accept PM's.

I do have a couple of magneto repair shop suggestions, PM me and I will let you know my experiences.

John


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