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Old 11-25-2010, 11:53 PM   #76
kbasa
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crankcase breather, I bet.
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Old 11-26-2010, 12:17 PM   #77
fadingfastsd OP
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Hey guys, thanks for the input.
I've got the starter cover pulled and I'm checking out the crankcase breather.
It looks fine.

What about it can cause a rattling noise like that?
Just it coming loose? It was completely tight, both screws.
Specifically what do I check on it?
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Old 11-26-2010, 12:50 PM   #78
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I would be tempted to start the bike and observe. But if it's the round style, change it anyway to the newer reed type.
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Old 11-26-2010, 01:53 PM   #79
fishkens
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Quote:
Originally Posted by fadingfastsd
Hey guys, thanks for the input.
I've got the starter cover pulled and I'm checking out the crankcase breather.
It looks fine.

What about it can cause a rattling noise like that?
Just it coming loose? It was completely tight, both screws.
Specifically what do I check on it?
I'm not sure that there's a visual check. They just seem to crap out and start talking.

Or, as Renner suggested, it could be the rear main...

http://bmwmotorcycletech.info/oilingsystem.htm

NOTE that some of these types of noises are often confused with noises in the rear crankshaft SEAL (Turkey gobbler noises, honking noises).
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Old 11-26-2010, 02:31 PM   #80
Renner
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Get it honking again and mess with the breather while it's squawking, see if you can alter the noise.

I'm guessing it makes the noise once it's thoroughly warmed up. Take another 15min. ride then whip off the starter cover to expose the breather, etc...

Better yet, remove the starter cover and breather housing then run the bike around the neighborhood till the noise returns. Then fiddle with the breather while the bike honks away.

Don't run the bike in the garage without a big fan moving air past the cylinders for more than a few minutes.

The noise may be a sort of bilabial fricative caused by crankcase pressure passing a sort of reed, either a breather disc or a main seal.
Doesn't hurt anything but can be annoying...especially when your buddies begin making comments.
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Old 11-26-2010, 04:39 PM   #81
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I guess you could always consider it a matter of pride, like a Ducati dry clutch.
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Old 11-26-2010, 04:52 PM   #82
fadingfastsd OP
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Man what would I do without my own personal pit crew here to help?
haha

I took the starter cover off again, and the breather cap. Started the bike (it was hot already), and the noise started. I push down on the breather valve disc, and it stops completely. So it is the breather!

Now, how do I fix it and get rid of the noise!? The disc looks fine, no cracks or chips. Do I have to replace it with a new one? Or I read I can cut a new one from a circuit board?

Any way to refurbish this original one so it stops chirping?

THANKS GUYS!
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Old 11-26-2010, 05:11 PM   #83
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awesome

best if you can install the upgrade reed valve, part number 11 11 1 335 712
Hans of Hucky's offers it for $35.25. http://www.bmwhucky.com/010011.html
Or fabricate a replacement as you mention.
Maybe use a slightly heavier spring as well?

A better crankcase breather may be considered a performance enhancing modification.
Check out Udo Gietl's upgrade: http://www.omnilex.com/public/bmw78/kotb.pdf

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Old 11-26-2010, 05:53 PM   #84
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I replaced the one on my 74 90/6 about a year ago The breathers can be a real bitch to remove (as you may soon find out). I'd just replace it with a new style breather and be done with it for another 36 years or so.
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Old 11-26-2010, 06:09 PM   #85
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Sounds good, I will order a new one soon.
I may try and cut a new one form circuit board material, I have a couple old boards from some power supplies I blew up.

To fix the problem at the moment, I pulled the spring/clip/washers out, and I added 4 small washers on top of the disc. Then reassembled. This increases the springs pressure on the disc, and the disc/valve can still open, but it stops the chirping noise when it vibrates too much.

Seems to work for now.
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Old 11-26-2010, 06:19 PM   #86
Overdog
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When I pulled mine the disk didn't look bad....the spring probably just gets weak. Your "fix" may last quite a while.
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Old 11-26-2010, 07:29 PM   #87
fishkens
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Quote:
Originally Posted by fadingfastsd
I took the starter cover off again, and the breather cap. Started the bike (it was hot already), and the noise started. I push down on the breather valve disc, and it stops completely. So it is the breather!
Whew!

Now you can stop worry about your apparent bilabial fricative (WTH? ).
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Old 11-26-2010, 08:49 PM   #88
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Quote:
Originally Posted by fishkens
Now you can stop worry about your apparent bilabial fricative (WTH? ).
While in grammar school I'd heard (maybe incorrectly) that it was another word for fart... and it seemed appropriate
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Old 11-26-2010, 09:03 PM   #89
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Mine still gobbles. Never got around to fixing it. Am I damaging anything?
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Old 11-27-2010, 05:50 AM   #90
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no, not damaging.
mine gobbled till I got tired of it.

at first it was part of the bike's character, then it became more persistant and annoying.
(I hadn't heard one so enthusiastic as seen in FFSD's video.)

While trying to get my old disc breather out, thinking I could pull it with a skyhook, I had the bike nearly suspended from the rafters

Then I got moderately smart and looked through some archives... found a post on the Airlist by T. Cutter that recommended removing the disc & post and turning a woodscrew in the center bore, then using a prybar in class II lever mode with the fulcrum on a small block of wood placed on the engine case.
Using that set-up it came out in a very satisfying way.

But after installing the reed breather it continued to gobble-gobble-gobble when warm from a long ride so I replaced the main seal and that seems to have cured it.
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