Ariel Owners Motorcycle Club

I had to fit a replacement gear cover to my w/ng. I very carefully removed the old cover as to not disturb the valve timing. When I screwed the new one on, I could not turn the engine over! After a careful inspection, I noted the bush in the new gear cover was not flush on the inside, so I pressed it in flush and that solved the problem. When I was doing the ignition timing, I suspected the bike was lacking compression. It started, but didn't run very well. So, took the gear cover off again, and low and behold, the dots on the pinion and cam were 1 tooth out. How on earth that happened is a mystery but I do recall turning the engine over with the gear cover removed (to check it was turning freely).
The dot on the pinion is not that obvious, but as there are no other marks I guess it must be the one; see picture. Note I checked with nut removed.

So, I moved the cam over by one tooth, reassembled, did the ignition timing and again it starts, but only on full advance, then stalls after 5 secs or so.

So, I asked around and one chap said to me was the piston at TDC when I set the valve timing. Looking in the manual, it does not mention this at all. Is this a red herring?

Can the dot on the pinion be relied upon or are there any circumstances where being 1 tooth out is correct?

I need to rule out valve timing being the running issue.

Cheers

Steve

What matters is that the tooth on the crankshaft pinion marked with a dot
meshes with the gap on the camshaft pinion marked with a dot. I haven't
a clue if the engine is at TDC when this happens so it can't matter that
much.

Everything is keyed together in the bottom end so if the valve timing is out
when the dots are correctly meshed some is seriously adrift elsewhere.

Thanks Will, that is exactly how I have set it up (the picture was just to show the poor indent in the pinion).