:agree: I have seen this happen quite a few times...not directly from the RIS cap but from caps not venting properly...that is your issue for sure tho...thats a shame, all that hard work ruined do to a lousy crafted gas cap....I would fade to black on them and make sure they knew....:edit:...They are members here..have a couple different user names I believe..they generate alot of concern when they are mentioned...here is a dated thread about these capsIt is your RIS gas cap!!!! No venting and the vacum is doing that to your tank. There have been several posts on this happening with his stuff.
Great point and my exact thoughts. Not a good situation if I was R.I.S. If you do use air pressure please show us the results.Maybe this will help.The pump can not do that to the tank. The bike would die before that happens. What happen was you filled the bike up on a hot day. Parked the bike in a cool night. Happens a lot to my fuel jugs here on the farm. And yes its from not having your vent working. I tend to keep my jugs out of the sun.
If you put a plumbers plug in and pump it up that kind of dent will come out.
I'd use a rubber mallet and tap around the dent while putting air in.
Ice will split the seams.
Just depends on how heavy she is.....Structurally the tank is not built to withstand much vacuum at all (obviously), which is why the stock setup has a functional vent. I work on pressure vessels rated upwards of 1500psi, and it is amazing how easily they will collapse with comparatively little vacuum. Different design principles involved. Vacuum breakers are a wonderful thing. Or in the case of RIS, a proper vent would've been a good idea.
Thermal expansion of gasoline is 0.069% per degree F. So, OP puts his gas in when it was 85F, drove home and parked. Overnight it drops to 55F. That's a 30F change in temp which would result in a 2.07% change in volume of gas in the tank. Doesn't sound like much, and it really isn't. If we were talking pressure, that is not even close to creating a problem with our tanks. But in this case, the volume contracts, and in a tank with no vent, that creates a vacuum. Vacuum is an entirely different animal than pressure. Without a vent that 2.07% reduction in volume would likely cause enough of a vacuum to collapse the tank. In vacuum terms, even 1-2"w.c. is a lot. That's INCHES of vacuum, not psi.
On the other hand, the picture above looks a lot like the imprint from a particular body part that, if positioned properly on the motorcycle and accompanied by a vigorous physical activity, could quite possibly have caused that dent pattern. :dontknow:
I'm just sayin..... I would NEVER use my bike for that type of activity...8)