Not sure where i mentioned the detent plunger but is a possibility. Could see me going into a long spiel though about gear engagement dogs etc. But hope you get it sorted. Love the DT2 & had a lot of fun on mine.

I'm not sure why you would think the plunger is small? It's a fairly close fit into the hole as I remember it. I guess if it's in there worst case is you'll end up with a spare.

You might check and make sure you have the correct spring too. I've never tried it but I can imagine having a correct spring installed without the plunger might be problematic?

Maybe I'm thinking of the later bikes though... they had a hollowed out plunger that slipped over the spring so if it was missing the spring might jam on the cam. I looked a pic of the one that fits the earlier models and it looks solid.

It simply didn't have the sort of gunge up there that might jam something in. Oil was warm and clear, and whatever I was prodding wasn't going anywhere. Looks like the plunger has a slight conical shape to one end of it, presumably to sit in the top of the spring. There was no conical feel to whatever I was prodding at. I felt I was prodding at something substantial. The spring also looked like it was meant to be there. It slotted snugly into the plug at the bottom.

Even being a DT innards novice I'm confident, given the other essential bits missing from the bike, that the original is in the bottom of an oil recycling plant somewhere.

Anyway, infuriatingly, my local-ish UK bike breaker, which has by the looks of things at least six or so '69 to '73 DT bottom ends, and innards from many more, simply wouldn't even check to see if there were any plungers in any of the scrap or even good motors. I even sent photos of where to look. In the time they spent giving me reasons why they couldn't look they could have removed all of them.

Instead, I've had to order one from Texas. Grrrrr.

Right, plunger arrived waaaaaay ahead of expected delivery date thanks to Ds Cycle Connection in Terrell, Texas.

Now installed - there clearly wasn't one already stuck in there - and just waiting for a break in the rain here in the UK (should be all done by March...) before I get out and see if I have fifth gear on an ongoing basis...

OK, so thanks to the fantastic expertise and knowledge on here I now have all five gears on a seemingly ongoing basis.

Utterly brilliant.

Many thanks for the input, guys.

Great news - another satisfied "customer"!