Problems with cam replacement (1991 GSF250)

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Hi, my name is Chris, fairly new to the forum (have been lurking silently for a while) and I've just bought (well a few months ago) a 250 Bandit. Have ridden bikes a few years ago but then had a bit of  a gap, just getting back into it.

Anyway I thought I'd give it a service and checked the tappets - sure enough they needed adjusting, so I took the cams off, put the new shims in and set about putting everything back together.

Problem is, I can't seem to get the cams in properly. I'm following the instructions in a GSX250F service manual (same engine) to the letter:
 - Put crank to TDC
 - Fit exhaust cam, lining marks up as described
 - Pull up slack and fit chain to exhaust cam
 - Fit intake cam, making sure there's 16 pins between marks on cam sprockets
 - Install journal holders
 - Fit cam chain tensioner

I have tried this 5 times so far. The chain is always worryingly slack between sprockets, it doesn't look right. Sometimes it slips off completely while bolting up the journal holders meaning there is then only 15 pins between sprockets. Other times I am able to bolt up the  journal holders, but then the crank refuses to turn - I suspect somewhere the chain is getting jammed.

Am I overlooking something really obvious here? So often it's something really simple, but I am losing my mind trying to get it to work. It's gorgeous weather here in NZ and I just want to go for a ride :(

This is the manual I have been using:
https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B8ODLPFUxFTpOTY5ZjA4MjgtNjllNi00YWViLWE0ZjctMDYyNGJkODhlZWJh&hl=en_GB

Any help would be much appreciated.