lol you aint the first geoff!
i rebuilt kengtir's engine after someone else had rebuilt it a year before and only put one nut on the tensioner as they had snapped the other and left it like that:shock: :shock: thats what led to the demise of that engine! was one big mangled mess of broken parts.
ok in answer to question, by all means try another tensioner but it could well be an overstretched timing chain or the banana chain guide has worn through the nylon plastic covering, which is a bitch of a job to do with engine in situ. is far easier to drop engine out and fix it.
however tensioner is accesible through the top, but its a knuckle scraping job unless you have little girly digits that can get in small places:lol: