I've now acquired a second A65 oil tank.
This one has the upper rear mount lug broken off.
The first one had the same but with a piece of 3mm thick plate welded on where the old lug broke.
As in welded on with a nice fat weld right on the seam of the tank where it will cause a stress fracture quite quickly.
Looks like BSA tried to spread the stress to avoid cracking the tank.
In this they seemed to be successful but the bracket breaks off instead.
I'm just wondering if I can design something which will beat BSA's original design and produce a mount that will locate the tank without cracking, breaking, or tearing a hole in the tank.

I would have thought the problem was more likely to have caused by the way someone had bolted the oil tank rear bracket to the frame and whether they had properly rubber mounted it. If the tank was badly mounted on its locating rubbers, it's probably all too easy to tighten up the rear bolt assembly to try to pull everything back to where it should be and end up over-stressing the bracket.

If the tank is properly fitted and the rear bracket is properly lined up with the frame bracket, I would have thought there should then not be too much stress on the bracket - it's basically there to provide a steady rather than carrying any oil tank weight. If it was me, I would simply weld on the missing part to the existing bracket and definitely not apply any weld to the tank itself..

 

I n same situ, I just welded a piece of 3mmplate, drilled to suit and mounted on a lump of rubber in hope of minimising vibration damage.

Seems OK, tho very little use.

Mike

Many thanks for the replies.
Having acquired two identical tanks both with the same damage, and looking at the same items for sale on a well known auction site, I had concluded that it was a design weak point.
Point taken about the correct fitment of rubber mounts, I've seen some incredible bodges over the years, amazing mechanical ignorance from people who should have known better.

It's not that obvious how the rear oil tank bracket should be held in place against the bike's frame and, to be honest, I struggled a little to remember how it went. The problem is that it is all too easy for someone to have simply bolted the rear bracket rigidly to the frame with the result that the bracket becomes stressed and eventually fails. When assembled correctly, there should be no metal to metal contact between the rear bracket and the bike frame with a rubber bush providing the required isolation.

It may be a case of PO's omitting the spacer (item 2, plate 13) that fits into the rubber bush. On my pre OIF Firebird I will use a shouldered bolt instead of BSA's bolt and spacer tube to prevent this happening. Also the 3 rubber locating bushes (item 41, plate 10), I assume with time, will degrade thus causing the tank to 'rock' more than it should perhaps.

Here's a previously posted pic of how the rubber bush mounting is supposed to look. The bolt obviously tightens against the spacer leaving the rear oil tank bracket free to rock on the rubber bush.