The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: Josh Cox on 26.04. 2009 01:08
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Removed the gear box foot set screws last night (bolts the gear case to the centre stand), these are different sizes and threads, not original.
What are my options for returning to original:
1) replace gear box case....
2) can the offending hole be filled in and redrilled / tapped ?, is welding an option ?.
Thanks in advance.
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You don't say whether the threads that aren't original are stripped/dead Josh.
What I have tended to do where I've encountered a funny mix, requiring a silly mix of tools etc, is to put up with any non-standard female threads that are in a good state, especially if they into aluminium, but make new screws, bolts or nuts using BSF-sized hex bar incorporating the 'wrong' thread. The correct spanners fit and the thing looks right. I know a lot of other people who do the same, usually on much shinier bikes than mine ( . . . because most bikes are much shinier than mine). There's no engineering reason not to . . .
If the threads ARE stripped or damaged, having drilled and re-tapped to the nearest size that'll work (in any thread form to save wasting metal) I again make the fasteners in BSF-size stock. Again, looks right and the tools fit. The fact that the screw shank is oversize for the head doesn't matter a lot. Main thing is that everything goes together properly and securely.
In the worst case though, where the holes are already oversize, AND stripped, AND there's not enough metal left to re-tap or helicoil . . . then it's a welding job or find a better case per your option 2). Lumiweld types of product can work well if you can get stuff clean enough.
Good luck!
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Josh,
Hard to tell from your post just how bad the threads are. Perhaps they are within range of helicoil repair. Here is a link to the "Recoil" catalog page::
http://www.alcoa.com/fastening_systems/commercial/catalog/productcatalog/Alcoa_Recoil_Catalog.pdf
If I am reading my parts book correctly, the thread you need is 5/16-18 Whitworth, and the kit for these inserts includes a 21/64" drill bit. If you had a bit that size, you could take the shank end and see if it is too big for the existing holes in the bottom of the gearbox. If so, then the kit should work, if not, you could consider going up to 3/8-16 Whitworth (or, maybe any 3/8" thread, having left behind the world of original size). The 3/8-16 Whitworth kit includes a 25/64" drill bit.
I get my helicoil kits at www.britishfasteners.com , however, the pictures they have online do not match the sizes, which is why I've attached the actrual manufacturer's catalog page.
Hope this helps.
Richard L.
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Josh,
BEWARE!!! these threads could contaminate your entire machine.
step 1. carefully remove the gearbox.
step 2. carefully wrap the gearbox in bubble wrap.
step 3. send it to me for disposal.
always ready to help, cheers
ps: better send the clutch too (just in case)
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Thanks for the feedback, I am happy to have different threads in this spot, was wondering if there was an easy way to fix.
Both holes has been retapped, one is 5/16 and the other 3/8 in some thread other than BSC, both quite servicable, will go with the make two different bolts with the same bolt head, easy enough done and still very presentable.
Whilst doing these restores I guess we can aim for perfection as found in some purist utopia, but settle for a few compromises, guess this will be one of them for me.
Olev, thanks for the concern *smile*.
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Josh,
Wow, I think the utopian purists crawling under your motorcycle to make certain the heads match on your gearbox foot set screws will be well pleased. Myself, I would let them whine and wail and gnash teeth, upon seeing two different sized heads. (These utopian purists are figurative, are they not?)
Richard L.
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The threads ought not to be Cycle into aluminium alloy Josh - they should be WW as stated. UNC screws might have been used as the pitch at both 5/16ths and 3/8ths is the same at 18 tpi and 16 tpi respectively. The across the flats head sizes of UNC/F hex screws/bolts are different from british stuff and the thread angles are 60 degrees not the 55% of all Whitworth and BSF fasteners. BSC is very fine at 26tpi in all small sizes and many large ones, with a 20tpi option as you get big. Not suitable for aluminium. Perversely, Cycle is also a 60 degree thread, like UNC/F and metric but the head sizes follow WW/BSF so the spanners work.
If the holes are serviceable, I'd use good screws and not mess with th holes at all. If you really want to be sure you're WW not UNC, run WW taps down the holes - then you'll have at least British imperial thread forms which take our sort of spanners, even if the holes are different sizes!
A good reference site for looking at all threads and pitches etc etc is www. mdmetric.com They've been to a lot of trouble to provide a comprehensive and very useful service, which also covers all sorts of tech subjects beyond threads.
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Are they in good condition do they bolt up securely, if so why not keep them ?
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Manosound,
In this case the "purist" is one that others would claim is mild OCD.
Thanks gents, over and out.
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Roger, wilco.
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Update on those pesky Gear set foot screws, have finished researching, nearly time to make a mess.
Original size is 5/16, one of mine is 3/8 (UNC), should both be 5/16 BSW.
Three options :
1) Weld up the offending hole and retap, do not like this idea as the welding will put a fair amount of heat into the case, sub optimal,
2) drill the offending hole a heap bigger, put in a 5/16 BSW insert, sub optimal, or,
3) Drill both out to 3/8 BSW, helicoil them in 3/8 BSW and replace with 3/8 BSW screws, also the addition of holes in the screw heads so I can lock wire them in place, best option I believe.
Will post photos when I do it.
Still satisfying the OCD urges.
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Have just fixed up the Gear Set bolts, went for the 3/8 BSW/UNC.
Drilled, tapped and recoiled, used loctite on the helicoil, cleaned out excess loctite with CRC.
Pretty happy with the result.
Before hand
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi113.photobucket.com%2Falbums%2Fn229%2FJoshuacox_2006%2F13MAY09003.jpg&hash=29f5cb84f6b84a5677d704f863056fc140e434ff)
Drilled for helicoiling
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi113.photobucket.com%2Falbums%2Fn229%2FJoshuacox_2006%2F19MAY09022.jpg&hash=0ee9d421cd2a041ca7fafb78c85d14f07899d615)
Tapping
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi113.photobucket.com%2Falbums%2Fn229%2FJoshuacox_2006%2F19MAY09026.jpg&hash=53c5a2cc19aab77f3cd3558dc8c7c4138742752d)
Helicoiling
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi113.photobucket.com%2Falbums%2Fn229%2FJoshuacox_2006%2F19MAY09035.jpg&hash=74ecd1ac02d268a155bbd1c64d708bd8505976e7)
Finished
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi113.photobucket.com%2Falbums%2Fn229%2FJoshuacox_2006%2F19MAY09041.jpg&hash=3bc7a7ad44df6aa749da7a1fb7898f764d099f0c)