Hi everyone, I've recently had a problem with the standard oil tank caps on my 1962 650 SS slimline loosening up & then disappearing off into the scenery despite making sure that they are done up tight before & during each ride, they've never done this before in the 35 years that I've owned her. I've lost two in rapid succession & the only reason I haven't lost a third is because I've chained the bastard on, but even so at the end of a 10 mile ride I'll find it hanging by it's chain & the inside of my right thigh oily : ( Has anyone else had these problems ? The first cap I lost was the original cap & the others are recent purchases but good quality English made ones, at around $55 a pop it's getting a bit expensive !
The oil tank cap is held in place like the Fuel cap: it is holds onto a collar via a 'bayonet' style fitting, and the claws of the cap are tensioned against that fitting with a spring inside the cap. Even if it works loose, the cap should not be able to undo far enough to come adrift, because the cap's claws should stay engaged with the bayonet fitting on the collar.
Could be that your new caps are not engaging the bayonet collar of the tank, or perhaps the collar is worn.
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The collar is good, the bayonet clips on the cap are as new, i was wondering if it might be a build up of pressure in the oil tank, I've checked the breather hole in the cap, I haven't checked the breather tube exiting the tower yet but even so it shouldn't come loose, especially as it's never done anything like this before. The bike runs very smoothly too so I don't think vibration would be playing a major role in this !