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Old 03-25-2012, 07:27 PM   #1
jjwithers OP
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Joined: Apr 2011
Location: So-Cal
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Question BMW starter cover venting questions

I'm building another R75/5 cafe bike and I am thinking of putting a solid cover that covers the starter and extends back to cover the upper transmission area (in place of the airbox).

I will mount the air filters directly onto the carbs.

My question is regarding the rubber vent above the starter and the crankcase breather?
If i put in a new efficient, lighter starter, and have air filters on the carbs, do i have to worry about that hole?
As i understand it, that hole is a way to circulate fresh air into the airbox and also cool the starter.

Regarding the crankcase breather valve on the top of the engine, Can i connect that to a basic filter or catch can inside my cover? or does that need air from the outside?

Thanks in advance.

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Old 03-26-2012, 04:39 AM   #2
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The crankcase vent is just that, it relieves the case pressure from the downstroke of the pistons. You can put a filter on it to catch the oil mist, no return air is required.
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Old 03-26-2012, 08:11 AM   #3
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Location: Los Angeles
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What he said.

R65's have a different vent that goes straight up and may be desirable, you could route a hose up and out the back fender like Triumph did. A filter placed locally to the breather would be fine as well. I know you clean your bikes, so the oil mist accumulation will not really be an issue for you. I have an R65 breather with a hose leading to a catch can living next to my battery.
Hope to see you at Willow!
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Old 03-27-2012, 01:17 PM   #4
Joined: Oct 2010
Location: Nor Cal, USA
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"...regarding the rubber vent above the starter ..."

That's the main air intake for the motor (air goes in there, back to the filter, down to the carbs...). If you have carb-mounted filters, you don't need that opening. The starter doesn't need "cooling."

Separate need to route the crankcase vent hose (and catch-can?) somewhere.
1974 R90/6 motor w/1050 kit; twin plugged; installed in...1970 R60/5 frame; RM125 front end; KZ1000 Police Tank.
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Old 03-27-2012, 07:20 PM   #5
jjwithers OP
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Location: So-Cal
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Thanks guys. Those were my thoughts and i'm glad you confirmed my shaky knowledge.

And hello Mike! I hope all is well. Life has been way too busy for another Willow trip. But it will happen again someday.


I'm thinking of making a small catch can inside my starter cover, sitting above the transmission (i have the space).

One can always pop of the cover and drain the can if necessary.

My cafe bike (with R100 engine) currently has a small filter attached to the hose coming from the breather (i use an airbox block off plate with air filters on the carbs) and i have yet to see it leak oil. I've got about 2500 miles on it and my longest ride on it has been probably a full day's ride (yet only 200 miles).

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