Hi, does anyone know where to get the square inner primary chaincase nuts? I think they're welded into place, but a few have bad threads and I'd like to replace them. Cheers, Glenn.

email (option): glenn_mullan@postmaster.co.uk

Glenn I doubt you will ever buy them anywhere unless you find a scrap inner chain case. I would simply take some suitable size flat bar and you or your engineer drill and tap a series of 2BA threads. Then just saw it into required lengths. You could probably make them a bit longer for ease of welding. Ron

email (option): ronpier@talk21.com

The correct thread for the primary case screws is 3/16" Cycle thread...

2BA is often used as a substitute due to the fact the screws are easier to obtain, the threads are similar (but not the same) and correct identification of the original thread can be difficult..

It is worth noting that there are various 'similar' threads but they are never truly identical or interchangeable...

3/16" Cycle thread has a major diameter of .1875" (2BA is 4.7mm or .185")...

3/16" Cycle thread has 32tpi [threads per inch] (2BA 31.3tpi)...

There may well be differences in other essential dimensions of the thread form but I would have to look those up...That may be the reason why there are so many cases with stripped threads...

You should be able to find 3/16" Cycle thread taps from Tracy Tools or The Tap and Die Company for example...

You would need to search relevant fastener suppliers for the correct screws...

Alternatively you could change them all to either 2BA or 5mm...Once the work is done it would make little difference as no hexagon head sizes are involved...Ian

Ian I did actually think they were 3/16" BSC but I checked your thread specs in the technical section before I replied. But Draganfly and others will always supply 2BA which is what I have on mine. From memory the battery carrier acorn nuts are also 3/16 BSC. Ron

email (option): ronpier@talk21.com

Yes..I believed they were 2BA for a long time until I got down to it and checked carefully following a previous post on the subject...

Logically BSC is the most likely thread as BA wouldn't normally be used in that type of application...

I must get Henk to change the information in the thread Tech Section....

I guess Draganfly have made the same error...Ian

Thanks Ron and Ian for the information. At least I know what I need to do. If Draganfly supply the incorrect chaincase screws, have you any idea where I can source the right ones? Glenn

email (option): glenn_mullan@postmaster.co.uk

Glenn I don't think these 3/16 BSC slotted cheese or filister head screws are going to be readily available. I've been looking at thread charts and see that 3/16 BSF are near identical as both are 32 tpi. But again you wont find them at your local Screwfix shop. A quick search on ebay found these.

http://www.ebay.co.uk/itm/3-16-BSF-SCREWS-STEEL-BRIGHT-SILVER-PLATED-ENGINEERING-FIXINGS-MODLERS-/301808246578?hash=item46452c5f32:g:wGAAAOSw~bFWLk2y

I have three BSA primary cases to deal with and all are fitted with 2BA screws which are 31.3 tpi. All screwed in fine and no problems even after several times on and off.

Works for me!!

I know others have used 5mm screws, but I guess you'd have to re-tap the threads.

Ron

email (option): ronpier@talk21.com

You have be be pretty strong to get M5 in there as without running an M5 tap through that hole. Could be a good idea if the threads are in bad condition but rather not. I just made a few of these nuts for my current project and silver soldered them in place.

Henk.

email (option): ahum@quicknet.nl

I don't see any problem here with changing the 3/16" BSC thread for another if both the nut and screw are changed...

However, I would point out again that threads are not interchangeable as no two threads are the same...If they were they would be the same thread and called the same thing!...

If different fasteners are mixed the resulting fit will not be correct and this is a practice which should be avoided...

Diameter and number of threads per inch are just two of the dimensions relating to a thread form...

For example..BSF and Cycle thread at 3/16" diameter share the same tpi and nominally, outside diameter...

However, BSF is a Whitworth thread form with an included angle of 55 degrees whereas BSCY has an included angle of 60 degrees.

Effective diameter, radius and particularly, core and depth diameters are also different, the latter two by .004" and .007" respectively...

Fasteners can be mixed obviously, but the idea shouldn't take route that different threads are either the same or interchangeable..they are not and are not intended to be.

It is better not to go for that solution as a first choice..Ian