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Old 05-18-2015, 09:21 PM   #1
Souljer OP
Recycling Electrons
 
Joined: Sep 2013
Location: Los Angeles, Ca USA
Oddometer: 237
BMW aluminum Air filter-Box - '80s-90's era. Filter fitment?

Hi,

I just got a BMW aluminum air-box. The later square kind.
I'm not sure when these were made but the part seems to be official BMW. However they do not seem to fit the filter.

I have always liked the older air-head motors with the aluminum covers front and back. Just seems more unified and organized rather than looking like different random parts stuck together.
Anyway, I found this and thought, just for fun, I'd try it out and see how it looks/works etc.

However the top does not fit the filter too well.
The top and bottom of the filter frame have a groove that the wall of the boxes fit into. The bottom is too thick also but not as bad since the bottom of the filter is a soft rubber seal and is forgiving.

The top is the harder plastic of the frame. The plastic lid is thin walled and fits in this groove fine.
The walls of the aluminum box are too thick to fit in the groove. It's only a few millimeters too thick and the wall thickness varies.
I was just going to grind it down to a thinner wall there so it will fit like the plastic lid.

When I put the two tops together (like hands praying) I can see that the outer dimensions are basically the same.
It's the wall thickness that's the issue with the inside wall of the groove on the filter.

Anyone have any experience with these?
Anyone know if they used a different filter for these?
They seem rather course and rough. That might just be from someone blasting them clean though. I don't know.

Any information or guidance appreciated.
Thanks.
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Old 05-19-2015, 04:02 AM   #2
airsmith
airhead wrench?
 
Joined: Jun 2013
Location: raleigh nc
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the cast cover can be dremeled out to fit the later filters.. the plastic cover actually works better in all repects(airflow,fit, ect) the funky little holes drilled in the front horns of that cast cover were a fix to help solve the airflow problems.. filters that work with that cover can be found if you are doing a show bike restoration..(note pulorlater # cast into cover)
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Old 05-19-2015, 06:59 AM   #3
Darryl's bmw
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Oddometer: 245
The aluminum airbox is from a 1980 model, and airfilters are not made anymore from BMW. You will have to trim it to fit.
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Old 05-21-2015, 04:47 AM   #4
Souljer OP
Recycling Electrons
 
Joined: Sep 2013
Location: Los Angeles, Ca USA
Oddometer: 237
Hi,

Thank you for the information.
I did grind down the edges and it fits together correctly now.

When installing it seemed like the carb intake pipes were not lining up very closely with the holes from the air-box. Is this normal?
I thought the bottoms were identical. The pipes were about a quarter of an inch off.
I ended up just stretching the bit of hose there over the gap and clamped down everything as normal. I guess that will work.

Need to change my neutral switch from the handle bar while I've got it apart and then I'll test it out tomorrow.
I put everything back on just to see how it looks. It looks good. The filter is still a black line but the back end of the engine is now all blasted aluminum above the transmission and matching the engine block.

I did notice that the original plastic top has two horns and they are both different - one is smaller than the other. The aluminum top has both the same size.
You mention that the small holes on the horns are to help or correct the airflow? How is that supposed to work? What is wrong with the airflow?

Thanks for the education. I appreciate it.
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