Brother, we need to have something in that second photo for scale... like a penny.

After some further investigation I found the source of the spring piece I found in the front main bearing carrier oil hole. The oil filter pressure relief valve was the culprit.If I'm following the oil flow diagram correctly I think the offending item has stopped short of the front main bearing and causing too much damage

That's item... 11 11 1 337 576 "Compression Spring - L=16MM"

However, I don't think it's job is "oil pressure release" in the normal sense of limiting the maximum oil pressure. The spring is far to light duty for that job. It's much more likely that the spring-ball combination act as a one-way valve, so that the oil system retains oil over night. Otherwise, oil would back-flow due to gravity. By having this setup, each engine start has oil already filling all the oil galleries.

Since that job requires minimal spring pressure, I don't think you'll see much damage resulting from that broken coil. Still it's an interesting find.

Here's some background information on why it's a good idea to have an oil check valve....

There are lots of older BMWs from the 1970's and 80's still happily running around. But during that same time Honda offered the CB350 and CB450 twins, and sold them by the millions. Where are they ? Based on sales records, there should be 10 of those for every BMW on the road. The answer is... they are all dead and made into beer cans. Lots of people know that, but very few people know why.

Both these vertical twin models had identical oiling systems, and neither system included an oil back-flow valve. Since the oil drained back into the sump each night, the oil delivery system started each day dry. Due to the design of the oil system, oil went immediately to the crankshaft, but it took as long as 60 seconds for oil to reach the overhead cam boxes and camshafts. :dry:

Americans have always enjoyed cranking their motorcycles and reving them wildly to prove they were running. So the cumulative effect of that 1 minute of run time without oil on the camshaft is what killed all those Hondas. Today you can only find the CB350 and CB450 motorcycles in museums, simply because of the missing oil back flow valve.

File that information under interesting, but useless !! 😛

Yes from what

Yes from what I have read it's purpose is to open when there is high oil pressure mostly likely cold starts then close as the engine temperature increases and oil pressure decreases. Whatever it's purpose is? it has the potential to damage your engine. I like your story about the Honda's missing in action.

Yes from what I have read it's purpose is to open when there is high oil pressure mostly likely cold starts then close as the engine temperature increases and oil pressure decreases.

See: http://bmwmotorcycletech.info/oilsketch.htm

• Your item is #6, oil bypass valve, and according to R. Fleischer breaks the spring (just as yours has) quite often.

• The lubrication system also has an oil pressure release valve (#12), which limits the maximum pressure to 75 psi.

Both valves are similar in that a piston or ball, opposed by spring pressure, is pushed open by the engine oil. However, simple intuition tells us that the valve assembly with the stronger spring is the one limiting the pressure to 75 psi when the oil is cold. This because that particular spring would have to oppose the oil pressure with a force equal to 75 psi. The unit with the weaker spring then is merely a check valve.

Hope this clarifies.