Rethreading nuts and bolts
 

Gentlemen ... So if I was to purchase tap and die to clean out or rethread nuts and bolts on the cab (such as the captured nuts) and chassis ad-ons of my Blitz - what specs would I be looking for?

The Canadian CMPs were pretty much all National Fine and National coarse, with the exception of the wheels, which had left hand and right hand BSF...5/8 for the studs.

Taps and dies are not ideal for rethreading, and I find that you will wear them out fairly quickly using them to re-thread. The proper tools are thread chasers. A good kit of those will run you around $100 to $150, and last much longer than taps and dies. Photo below is a kit I recently purchased, sold by Gray tools, and I have been very happy with it. You can also buy sets of thread files which will have most of the threads per inch on them for chasing some of the larger threads like on shafts. There is one included in the kit shown....I bought a set of four which included metric threads as well as UNF/UNC. However, it is missing some of the TPIs used on BSF in case you get into the British equipment at some point.

Taps
 

Hi Dave

For your CMPs You need a common UNC and UNF set , older British vehicles typically used BSF and BSW threads . The BSF threads are a oddball pitch but BSW threads are same as UNC except for the 1/2" size and being 55 degrees thread angle. the UNC threads are 60 degrees .

Aust CMP nuts & bolts
 

Dave,

For CMP Chevrolet parts manufactured and fitted in Australia, the thread was Whitworth ie BSW (bolt heads & nuts made to conform to UNC/UNF spanner sizes) . Where Canadian drawings called for fine threads, GMH manufactured UNF thread bolts and nuts.

For fitting CMP Ford parts manufactured in Australia (such as the attachment of the cab roof) the nuts and bolts were BSW with BSW bolt heads and nuts.

Never as simple as it seems!

Mike

Dave, Depending on what state your captive nuts are in you may be able to tidy them up by cutting a groove in the thread of another bolt (cut off disc etc) If you lube (a bit of kero mixed with a bit of oil) and judiciously work your grooved bolt into the captive nut, you will likely clean it up. Don't force it. back off add more lube and have another go.
Btw,fyi, most fasteners have a rolled thread which is stronger than a cut thread. It means the "grain" in the material follows the shape of the metal. The captive nuts were likely "cut" via a nut tapper. (just my guess)
If the threads are stripped you will need to replace the captive nuts. Seek out the right ones and take them back to original.

Most helpful - many thanks
 

Thankyou folks - all that info very helpful and much appreciated.

Morris and metric
 

Dave

A possible trap to be aware of is: Morris used metric threads on their engines , your CS8 engine has metric threads all over it. William Morris had an arrangement with Hotchkiss of France for engine manufacture back prior to WW1 I think so it goes , Morris eventually bought out a Hotchkiss factory that was setup in the UK making armaments during WW1 thus he inherited metric tooling

Sounds like you are going to need to order a couple of sets of pitch gauges, a caliper, and google some thread charts. After a time, you will start to recognize the threads on he bolts at least, but much harder to do on nuts.

Generally, these days you can tell the thread type by the head markings (but not always...I have seen standard bolts with metric grade markings), but those rules did not apply to the WW2 time period. The Hotchkiss name brings up another anomaly that I recall. Didn't they use standard threads but with metric heads on their M201 Willys engine production?

Ford did a similar thing in the 70s. With a Kent designed engine and German gearbox design in Escorts and Cortinas, meant a mix of both standards, and hybrid bolts.
Identifying from a bolt head has become far more difficult in the last 20 or so years with many new manufacturers.
The Australasian standard doesn't help.
Now that I think about it, even Ford of Canada made hybrid bolts and nuts for carriers with BSF threads and American (unified) standard heads.

Then there are the tool sets intended to cover all possibilities (eg 19/32", 25/32", and 29/32") made to fit British standard heads, as an extension of an American standard tool set.

Thread File
 

A very handy and inexpensive tool(s) are Thread Files.
These are similar to a regular machinist file but will recut burred or damaged threads on bolts. One ore two pass's with one usually does the trick. A Google search is your friend for pics and descriptions.
Harris

I'll second the thread gauge. Handy little device. I have one that folds up similar to feeler gauges.

Matt