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Hey there!

I have a custom CX500 that was recently completed. I put a few hundred miles on it so far, and noticed recently that the nut on the 12mm flange bolt below the engine (picture below) had rattled off.

I suspect this is because we put a custom exhaust on the bike, which is mounted on the same bolt. This meant the frame was essentially 1/4" or so wider, and as a result the nut likely didn't get enough purchase on the bolt to stay secure.

I think that if I found a longer bolt, the nut would be able to grab more thread, and would be less likely to shake loose.

I'm wondering if anyone is familiar with the process of finding a custom bolt like this - the stock one is 12x308, and I lost the original nut, so I'm also in the market for a 12mm flange nut to match with it (and a locking washer this time!).

Here's a photo of the bolt in question. I figure if there's something out there in the 12x315-320 range from another bike or something, that would suit my needs just great. Any ideas?
 

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Either that or go to a farm supply store where you can find bolts of all sizes and lengths.
 

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308mm is close to 12 inches long...
It is going to be very difficult to find.
I had a friend make me one from Stainless rod. He turned it on the lathe to reduce the size on end to fit a flanged nut which he TIG welded on and then dressed the welded face on the lathe. The material he used to weld the nut was cosmetically identical to the 12mm rod. He then threaded the other end to accept another flanged nut with as much threaded end as previous. It is gorgeous.
You want at least the nut's thickness engaged by the nut. Around 1/2 inch. Over an inch is threaded on the bolt in stock form. You will need to add length to accommodate your bracket and probably wouldn't be a terrible idea to thread the added length to extend how much of the bolt is threaded. That way if you didn't use the engine mount bolt for the exhaust later you could have that nut be proud of the nut...might not look great that way but it would keep your motor secure. You may need to use a lock washer, most of the time a flange headed bolt and flange headed nut do not require a lock washer. Apparently you may need this as it is not cinching down tight. You may need a little blue thread locker on the bolt.

The SS rod was about $25 and then the two flanged nuts and his time, not a cheap bolt. No, he is not interested in making any others. Sorry, not a source...but a solution.
 

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'84 CX650E that is evolving into a GL500
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And most stainless is about the strength of a grade 3 SAE bolt. Not to mention the possibility of galvanic corrosion. I certainly wouldn't use a stainless bolt to hold my motor into the frame.
 
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