After converting my '49 M21V2 to electric start, starting required a bit of fiddling with throttle / retard to strike a light. And so decided to fit an ATD to improve the spark at low revs. Starting is now much improved. However, when setting the ignition timing I was surprised by the lack of compression on the rear cylinder (finger over plug hole to determine which cyl was on firing stroke).
And so yesterday I took the rear cyl valve covers off to check valve clearances. All good, but with bike at eye level on the lift, noticed the exhaust valve spring retainer was touching the rocker arm. First conclusion was a worn valve cap but closer inspection revealed the cotters were low in the retainer.
So, head off to check that out (first time off since engine was built 30+ years ago). Exhaust pipes off, oil drain pipe from head removed, remove rear carb - hang on a minute, which twit designed that? It's so close to the oil tank it won't come off its studs. Yup, that was me when I built it all those years ago. Must change those studs for bolts ...
So, head was off and exh valve out. All was fine except for those collets in the retainer. Dug around my spares and found another retainer that provided a better fit. Would have made new collets had I known the taper BSA used, but wasn't prepared to extend the job by messing around with trial and error to make new ones.
Mislaid a rocker cover screw in the process so, as soon as I've found (or replaced) it it's tank back on and run her up to see if my oil feed mod is sufficient to supply the ATD with a little lube (I originally created a bleed off the quill feed to put an occasional drop of oil on the timing chain, but that's not enough for the ATD). Trouble is, the big ends are roller so oil pressure is low, meaning enlarging the hole feeding the chain may not prove sufficient. We'll see - if not, I'm minded to fit a small oil cup above the ATD and give it an occasional lube through that.
Day is getting warmer, so time to get back to the workshop ....