Good point. I was expecting to see the usual large synchros I'm used to in modern boxes. I will download a manual and have a look.
I have had the top off and there is nothing to stop the gears sliding together. They slide effortlessly up and down the shaft until the teeth engage.
Oldsub- neither box is original, according to what I think are the date codes. What came before the SM420? Something with identical dimensions that would bolt in where an SM420 appears to fit now? both my boxes have the pull up lever for reverse.
Thanks for your responses.
