The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: jg928s4 on October 28, 2011, 07:00:51 PM
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When shut down the Bike after a ride I hear a hissing sound at the left cyclinder. Sounds like a leak when the bike is cooling off. Is this normal? HAve not heard on right side, just left.
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There could be a little water trapped inside the gap between the valve cover and the cylinder.
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Was the bike just washed, or left out in the rain ?
Water collects on the cylinder head and takes some time to get boiled out .
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Been parked out doors, hasn't rained, but very damp in the mornings. hopefully that is it.
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The engine breather might make a hissing noise at shutdown although I'm not sure why it would be heard on the left side. Another possibility is an air leak at the oil dipstick. It must be air tight and there should be a gasket or O ring seal depending on year.
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should the aluminium dipstick have a gasket? Mine does not, but I do not think the leak comes from there.
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I think the original was an aluminum washer, like the fill and drain plugs have .
Here's a page from RealOEM.com .
It shows an o-ring instead on the later year bikes .
http://www.realoem.com/bmw/showparts.do?model=0364&mospid=51897&btnr=11_1721&hg=11&fg=42
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should the aluminium dipstick have a gasket?Mine does not, but I do not think the leak comes from there.
The dipstick seal is under crankcase pressure and without a proper seal it could certainly leak and interfere with the correct operation of the engine breather which is designed to pump down the crankcase to a partial vacuum. An air leak at any point into the crankcase will cause problems and besides the dipstick seal that includes the rear main seal and front crank seal. So even if you don't hear the noise from the dipstick lack of the correct seal could still be the primary cause of your problem.
Of course the noise could still be something else but either way your dipstick needs a good air tight seal.
I think there should be a gasket on the early metal dipsticks and an O ring seal on the later dipsticks which may be plastic. In practice the O ring works on both types. I would think there is no need for a BMW specific part. A generic Nitrile rubber O ring of the correct dimensions will work fine. If you need the O ring dimensions I'd be happy to measure mine.
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The BOM from image below shows two different dipstick part numbers for bikes manufactured before/after 9/80. The dipstick on my 1983 bike appears to have a plastic wingscrew.
What are the differences between the two dipsticks?
should the aluminium dipstick have a gasket? Mine does not, but I do not think the leak comes from there.
http://www.realoem.com/bmw/showparts.do?model=0364&mospid=51897&btnr=11_1721&hg=11&fg=42
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What are the differences between the two dipsticks?
The later bike has a slightly larger capacity sump so maybe the dipsticks are different lengths.
This is the best info you are likely to find on sumps and dipsticks
http://largiader.com/tech/oilpan/
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Another cause of hissing is the spark plug not being properly seated/tightened.
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Could be a small snake trapped in the battery cover. Hissssssssss
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After a good ride to work and back no more hissing.. Must have been the moisture.