Thank you 33d3 and Rex, I have a copy of Munro’s “BSA a practical guide covering all models from 1931”, which I have read and applied it’s settings to my bike. Your point about tappet clearance is interesting; page 189 shows how the exhaust setting changed from 6 to 8 thousandths of an inch from 1932 to 1933 for essentially the same engine. It’s tempting to rationalise that this increase may have been to reduce engine temperature by creating a bigger passage for hot gases.
I would like to make a reference from page 82 of the same book. Below is an excerpt for those who do not own a copy of the book.
Ignition
No improvement can be expected from an alteration to the ignition timing. In fact the reverse is almost invariably the case, too much advance producing roughness, without any speed increase, while a retarded spark causes sluggishness and overheating, although the owner may be tempted to retard his ignition a trifle in order to take advantage of the slightly greater flexibility thus obtained. Yet it is a certain fact that many owners re-time their engines as a matter of course as soon as the dealer’s back is turned. This is proved by the number of machines which find their way back to factory repair departments, or to repairer’ premises, with ignition timing hopelessly out. And it is significant that the complaints for which such machines are returned is often attributable soley to the experiment on the owner’s part.
I do not reference this passage for churlish point scoring reasons, merely to clarify my reasoning for not making changes that are not evidence based. It is with an orderly mind and a logical neatness that mechanics diagnose and resolve issues. Hence I will make a test table, which is my usual practice that records incremental changes made, the rationale for making the change and the outcome. This has ensured satisfactory conclusions for technical problems for me in the past.
I will include the following tests and changes, individually, within my causes of overheating test table
1, Weak fuel mixture
2, Burnt valves
3, Carbon build up
4, Insufficient exhaust tappet clearance
6, Increase exhaust tappet clearance
Finally, yes, I will be using Magneto setting contained within the “BSA Motorcycle Instruction Book”, but rather than use the “All models 1930 to 1936” I will use the “1932 Models” edition. The reason for this is that it has a clear diagram showing a Lucas Magneto with the follower about half on the start of the cam.
This image shows where I set the points to 3 thousands of an inch, which I now believe could be about 40° to late. I was informed to use this point by someone with significant knowledge of Magnetos, but I think he expected me to use this when the piston was at 3/8 before TDC.
I will let you know how I get on.
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