Hi,
Thanks for all your replies. I'm pretty certain the frame isn't the cause, as it's been said, a bent frame would hold the chainring at a single angle and not cause tight spots. I checked the frame welds for cracks after the crash but I hadn't considered I might have bent the frame. I might get the LBS to check it’s in line next time it's in the shop.
I can't put the old crank on as it completely snapped off one of the tabs and bent another one. I've had a cursory look to see if the chainring is parallel to the frame but I will check it out properly.
I've also tried flipping the chainring over and even another chainring, but the tight spot remains in the same place, so I’m pretty sure the rings are straight.
Top of my things to try is the loosen-off-bolts-and-tap-with-soft-hammer plan. I don't think there's that much room to move it on the spider, but I'm willing to give it a go and be proven wrong. It won’t be the first time. :o)
I had considered just running the system a bit slack but I'm covinced the chain will come off. I don't really want to run it with a tight spot as I’m convinced it will wear all the components out quicker, particulaly the freehub and bottom bracket bearings. I’d rather run it with a tensioner.
They're bl00dy silly these singlespeeds aren't they! Still, I can't stop riding it though. :o)
VC