There is a forest being lost behind all these blasted trees!
To go back where we started - heads falling off valves.
I accept that R65s, particularly the early small valve models, have always been somewhat more prone to dropped valve syndrome than the larger models. But I am yet to read a credible reason as to why that might be the case.
To my way of thinking the smaller stem diameter is not determinative as many, many motorcycles of Far Eastern origin run significantly smaller stemmed valves in air-cooled heads and their heads do not fall off.
Nor do I think temperature is an issue, an R65 runs no hotter than its bigger brothers (or sisters).
I know what causes the heads to fall off - over time the guide wears which means that the valve head no longer strikes the valve seat entirely square, each time it does so it deflects the valve head microscopically, eventually the total of the microscopic deflections causes a fatigue failure of the stem at the point of flexure.
My theory.
R65 valve guides do not wear any faster than any other BMW, but R65s, at least "back in the day" were marketed to and owned by those new to motorcycling and who may not therefore have been as on top of maintenance requirements as they might have been.
Other valve failure modes.
Sue mentioned that her 'lead free" replacement valves had just about worn the collet grooves enough to drop - this quite simply should never happen regardless of mileage on any quality valve. In the absence of a better theory I would suspect that the valves were supplied as "blanks" and after being cut to length and after having the collet grooves cut into them, were not properly hardened.
I have used blank valves of quality manufacture in the past, hardening the end where the rocker bears and the collets clasp is an important step. Mind you, the mucking about has long since resulted in me using pre-made valves, over the period of time I've owned the R100 I have used BMW OEM, Italian Ivam brand and more recently Swiss Intervalve (sold by Motobins). Although the jury is out on intervalve, at least as far as personal experience goes, my research did indicate a very high satisfaction rate.
The other thing worth mentioning is that there is no such thing as "lead free valves". The issue with the removal of lead from fuel is valve seat recession, caused by the absence of the lead "cushion" allowing the valve head to pound the valve seat into the head. You can, at very great expense, have "lead free" seats fitted, frankly unless the seats are otherwise in need of replacement this is a waste of money. Some valve seats will recede, most will not, only spend the money if your seat begin to recede - and then replace them with OEM, BMW spent a lot of time, money and computer resources to figure out how to greatly reduce recession, to my knowledge nobody else has done the research and blindly fitting a hardened "lead free" seat from the automotive world (assuming you can even find one) might work out OK or it might not - in either event you are a test pilot conducting your own outcome driven research...
