I think if I was having that much trouble I'd build one--either from a
delrin block or a roller. The tensioner on the TR3/4 is a pitiful steel
blade, but it doesn't seem to cause any problems.
We used to replace the rubber-faced stock tensioners on racing motorcycle
engines with home made delrin blocks so they'd stay together.
Another choice, and there might be too much slop in your setup to do this,
but you could try removing the tensioner or just having a fixed rubbing
block. The side of the chain that the tensioner is on whips when the engine
runs at speed--the tensioner doesn't do anything to the other side of the
chain--it's under a lot more tension than a little spring could exert. The
tensioner is supposed to keep the slack side of the chain from whipping. You
could let it whip a bit and see if that does anything nasty, or just fit a
rubbing block and see if that does the trick.
Motorcycles have a lot longer timing chain, especially the DOHC ones, and
chucking the complex chain tensioner and using a simple block to prevent
harmonic whipping is an old trick.
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