Threads, pitches and spanners.

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
good-hifi
Posts: 711
Joined: Thu Jun 08, 2006 9:14 pm
Location: OXON UK

Threads, pitches and spanners.

Post by good-hifi »

Here is one for the technically brilliant.

The 'restorer' of my bike forgot to mention a few issues to me when pitching the sale.

One thing he forgot to mention was that he had stripped the thread of one of the retaining bolt holes in the cylinder head and the rocker cover (Model 14) is leaking oil.

I have removed the rocker cover and sure enough a thread in the head is wrecked. What I want to do is helicoil this as it is very accessible in-situ.

I have measured one of the bolts with a thread gauge and it is 22g. The spanner size is 3/16 inch Whithworth. Now I always thought what 22g was for 1/4 inch Whitworth and checking on the net that seems to be the case.

So...two questions. Why is it a 3/16 inch spanner and what size helicoil do I need to obtain?.

As usual your help will be greatly appreciated and much lauded...

Cheers
Mick
itma
Posts: 7721
Joined: Tue Nov 22, 2005 6:01 pm
Location: UK

Threads, pitches and spanners.

Post by itma »

it should be 5/16 bsf Mick, the spanner size is irrevant, AMC did this a lot for rocker box bolts, BSA very fond of this sizing on nuts also,
don`t you mean TPI [THREADS PER INCH ]
gauge measure used for sheet and wire,
think the idea was to save space probably.
good-hifi
Posts: 711
Joined: Thu Jun 08, 2006 9:14 pm
Location: OXON UK

Threads, pitches and spanners.

Post by good-hifi »

UHOH!, I'm not sure what you mean by BSF, the spanner size or the thread?.

Has 22g on the thread gauge, and matches up to this chart http://www.spaenaur.com/pdf/sectionP/P108.pdf but yes it is TPI.

So I@m sort of doubly confused now (poor me) as to what helicoil size I need. And is it Whitworth or BSF....

Cheers

Mick
itma
Posts: 7721
Joined: Tue Nov 22, 2005 6:01 pm
Location: UK

Threads, pitches and spanners.

Post by itma »

you need a 5/16 bsf helicoil kit for the thread repair.
the spanner size is not relevant to the thread pitch.
I could give you the lecture on thread forms and spanner sizes, but the isn`t enough wine left in the bottle.
keep an eye on your email box
lawrence
Posts: 2453
Joined: Mon Jan 01, 2001 12:00 am
Location: NORTHAMPTONSHIRE UK

Threads, pitches and spanners.

Post by lawrence »

Unless you are going to use a lot of the helicoils it may be cheaper to get a local engineer to do it for you Mick.
RogerJ
Posts: 468
Joined: Tue Jun 14, 2005 1:00 am
Location: HEREFORDSHIRE UK

Threads, pitches and spanners.

Post by RogerJ »

A 5/16 BSF helicoil kit will cost you £24.75 plus P & P from Uni-Thread Ltd. (www.Uni-Thread.com). I bought a helicoil kit from them recently - excellent service.
good-hifi
Posts: 711
Joined: Thu Jun 08, 2006 9:14 pm
Location: OXON UK

Threads, pitches and spanners.

Post by good-hifi »

quote:
Unless you are going to use a lot of the helicoils it may be cheaper to get a local engineer to do it for you Mick.


Thanks Lawerence, The 'restorer' left me three threads to put right.

I might also just helicoil one or two other suspect ones so I'm rather hoping that buy purchasing a kit I will save some money. And of course be future proof for any other 'restorer' it is my misfortune to be conned by.....

Cheers
Mick
good-hifi
Posts: 711
Joined: Thu Jun 08, 2006 9:14 pm
Location: OXON UK

Threads, pitches and spanners.

Post by good-hifi »

'nother question.

If you were going to buy some taps and dies for using with classic British bikes, what BSF/BSW sizes would you buy.

The sets are all well and good but there are bound to be the inevitable sizes that would never get used and it beats me why suppliers don't do sets without the tap and die holder. The price range is astounding. I don't want to buy cheap 'plastic' ones but I also do not want to pay the astronomical sums that can be seen.

I'm sure the die hard restorers out her know exactly which ones are most commonly used.

Cheers
Mick
RogerJ
Posts: 468
Joined: Tue Jun 14, 2005 1:00 am
Location: HEREFORDSHIRE UK

Threads, pitches and spanners.

Post by RogerJ »

Mick,

I asked that very question about a year ago, if you do a search on my questions then you will see the various answers I got (you will also see the various other greenhorn questions!!).

If you are going to buy taps and dies then contact Tracy Tools - again I'm not a shareholder but they give good service.

Cheers, Roger

In fact the question was last October to do with Centre Web stud size.Edited by - RogerJ on 11 Aug 2006 11:28:50 AM
good-hifi
Posts: 711
Joined: Thu Jun 08, 2006 9:14 pm
Location: OXON UK

Threads, pitches and spanners.

Post by good-hifi »

Thanks Roger, will do..
Mick
Locked