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Sump drain bolt


Hi everyone, a naive question as per title. 

I have a 1948 model 18 and I am  unsure where the sump bolt is  as it is wet dumping if left for more than a week,  I can only see one bolt head 9/16 I believe  but it is so tight  that I don't want to do any damage, if it's the wrong one, hopefully  someone can point me in the right direction. Thanks in advance .Paul 


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......


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