valve
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Pierre Michaud
valve
The valves on my R69S are in excellent condition. From my 1968, R69 history, I have no way of knowing whether they were changed at one time for the non-leaded type or even changed at all. I have noticed however that the exhaust valve seats are non magnetic while the inlet seats are highly magnetic. I conclude from this that the exhaust seats are made from an alloy with no iron in it. As for the exhaust valves, they look as if they were made in two pieces. The flute part is "seamed" to the stem at about 1 inch from the base.Magnetic pick up is markedly different in these two sections. The pick up on the flute part is weak while it is strong on the stem. On the inlet valve I do not see this feature as the mag pickup is stong from end to end and I see no mating line on the surface of the stem. Based on these observations, can anyone tell me if my exhaust valves are original and if not could they have been converted to a non-leaded type (exhaust). Also, when a non-lead conversion is done, is it necessary to change the inlet part. Information tells me that only the exhaust side is prone to valve seat recession when using non-leaded gas on these vintage motorcycles.
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John Beyrau
Re: valve recession
In regards to the valve recession problem. I know of a couple of cases where it occurred. These were /6 and /7 engines and they both were machines that were heavily loaded and operated at fairly low rpm's by their owners. (Here in US we use the term "lugging an engine" for this. )
When I purchased my first BMW in 1978 ( a 1977 R75/7), the US had just banned leaded fuel. At the time I was told, by the dealer, that the valves in my engine would probably wear out about 20 % sooner ( e.g. 80k km rather than 100k km.) than if leaded fuel was available. This information supposedly came from the BMW factory, but I have never seen it written down anywhere . Since then I have ridden an R60/6 a1977 R100/7 and a 1981 R80gspd each has over 140k km on the odometer Also I have owned an 1978 R80/7 and currently have an R60US. NONE of these machines has had valve recession problems, though the valve train in the R80gs is getting pretty noisy as it approaches 220k km.
In conclusion, DON'T LUG YOUR MOTOR IF BURNING UNLEADED GASOLINE. Your valves may wear out bit sooner than with leaded gasoline then have unleaded seats and valves installed when doing the head service. Meanwhile sit down, shut-up and ride it.
When I purchased my first BMW in 1978 ( a 1977 R75/7), the US had just banned leaded fuel. At the time I was told, by the dealer, that the valves in my engine would probably wear out about 20 % sooner ( e.g. 80k km rather than 100k km.) than if leaded fuel was available. This information supposedly came from the BMW factory, but I have never seen it written down anywhere . Since then I have ridden an R60/6 a1977 R100/7 and a 1981 R80gspd each has over 140k km on the odometer Also I have owned an 1978 R80/7 and currently have an R60US. NONE of these machines has had valve recession problems, though the valve train in the R80gs is getting pretty noisy as it approaches 220k km.
In conclusion, DON'T LUG YOUR MOTOR IF BURNING UNLEADED GASOLINE. Your valves may wear out bit sooner than with leaded gasoline then have unleaded seats and valves installed when doing the head service. Meanwhile sit down, shut-up and ride it.