Sump drain bolt

Hi Paul,

   The sump plug on the 1948 (one piece rocker-box) engine is underneath the crankcases in a partial recess, so it's best to use a Whitworth sized socket to remove it. The plug is 3/8" Cycle thread which is too fine in aluminium and easy to strip the thread if over-tightened. This will mean you will have to address the wet-sumping, because continual draining will soon damage the thread in the crankcase. You might have to consider a tap or one-way valve on the oil feed.

... has been changed by a previous owner to a metric coarse thread which is better. I'm not about to strip the whole lot to replace something that works well enough......

Oddly...I fired up my 16H yesterday after several weeks lack of use. It has ( as far as I know) the original Mazac body pump. The oil tank still had plenty in it. Only about half had leaked through.  No undue smoke. I wonder if the mazac pumps were less prone to wet sump? The old ball bearing engines must have had far less oil pressure than Dommies with shell big ends, so perhaps they had to move from the cheaper (and better?) mazac to something a lot stronger.

... that if you leave the bike on the compression stroke it minimises wet sumping. No idea whether it works as I have a Yamaha non-return valve on my ES2 which seems to work perfectly. So far......

Could you not simply drain the oil tank? I do that on my ES2 as well as leaving it on compression although there's no need. Don't forget to leave the oil cap on the saddle as a reminder!!