Thank you very much for your support. Yes, I have been having a good look around, it seems with this type of engine a common issue due to oil back up. Please see attached screen shot. The reed valve is the likely candidate. http://books.google.co.uk/books?id=-kBjUSjIMYAC&pg=PA219&lpg=PA219&dq=s+%26+S+engine+reed+valve+oil+return&source=bl&ots=DJPSiBo2YV&sig=VLfCI0LREaRkdOlb5Wt8pV7_Tfk&hl=en&sa=X&ei=k67bU9C2OdLT7AaNz4CACg&ved=0CC0Q6AEwAg#v=onepage&q=s%20%26%20S%20engine%20reed%20valve%20oil%20return&f=false
