BMW K bikes (Bricks)

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Beamer

Beamer
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Here are close ups of the internals of the Bosch air flow meter used on the K series BMWs.  These include one with the later factory mod. which hard-wires around the dry point connections. Note extra wire on the wiper contact arm and the small wires from each pin of the external connector to the contact pads on the substrate.

These extra wires could be an impediment if we want take the plate out to file the holes in order to restore a clean wiper track on a defective unit.

The Bourns  production dates can just be seen below the wiper arm : 8932 , 8423 . I'd guess that is year and week number. The part number on the plastic cap is identical which means that these two models are indistinguishable from the outside. A lack of rigour which I find very un-german.


Early standard model:
Bosch air flow meter version differences Boscha13


Later factory modified model:
Bosch air flow meter version differences Boscha14

Also note the poor condition of this unit : the fine laser trimmed slots in the green rectangular resistors have gone all furry looking. I think this unit has been badly stored off the bike and that this is probably damage due to humidity. This underlines the need to properly seal these units if they are re-opened. It is probably a good idea to get a can of dry air ( used in electronic and computing applications ) and purge the moist, ambient air before resealing. [ Or at least seal in cold morning air not on a warm summer's day. Contrary to what we usually think, warm days may feel dry but the air contains a lot of humidity. A cold morning with 5 degree C air, an hour or two after sunrise is ideal ]



It's not quite the disaster that it appears to be though the resistor values are somewhat from where they should be and this will deregulate the output from the correct injection curve. They will almost certainly degrade further.


There is also the question of the sealant used. Common silicone sealants as used for sealing engine casings contain acetic acid which is know to be aggressive to electronic circuits. Whether it would affect the resistor board, I'm not sure.

    

Chocolate

Chocolate
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@Beamer wrote:A lack of rigour which I find very un-german.

Hey!
Nice to know there is a old and a new model air flow meter.
Thanks for the pictures!
I have tried to follow your air flow meter thread.
A bit to much writing for me :-)

I prefer short sentence like:
There is a old and a new air flow meter.
Beer = drink
Food = eat
Girls = !
Bike = ride
Immanuel Kant grounding for the Metaphysics of Morals, Categorical imperative = Bla bla

Cheers
From a very un-German :-)

P.S.: what would help me is, in short sentence
1.) How do I know the air flow meter is the issue?
2.) How can I easy test And find out it is good or bad?
3.) when should I replace?


__________________________________________________
Only a few activities make me experience my senses in a way motorcycle riding does, it is like swimming in the nude in a river.
K75 BA/1992 ABS, K75 BA/1991 noABS, Ducati, Mobylette M1/1973
    

Beamer

Beamer
Gold member
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Very valid. bottom line questions. That is where all this is leading.

The other thread is very long now since it is an exploratory discussion and testing, developing a test method and trying to divine what the set-up criteria are how to define a calibration procedure. Two weeks ago I did not know what these things looked like, how they worked and how the EFI worked to interpret the output. I now have a much better, though still incomplete knowledge. More fiddling / testing / riding and next week gas analysis should reveal more.

When that is finalised I will resume the whole affair in a new thread and this will hopefully address those questions.

My practical aim here is to be able to open the unit, move the resistor plate to get a clean, unworn track and reset the wiper index position with vane closed . This implies understanding the effect of moving it which is what all the plots and testing are for.

I just posted these photos here since I'd seen another post somewhere where a guy had done a hack to reproduce the factory mod. but had not shown the original factory version. I thought it would be useful to document this for reference here since I had come across and example of the later model.

    

robmack

robmack
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@Beamer wrote:There is also the question of the sealant used. Common silicone sealants as used for sealing engine casings contain acetic acid which is know to be aggressive to electronic circuits. Whether it would affect the resistor board, I'm not sure.
Very true Beamer.  The unit should be sealed with an electronics grade silicon sealant.  As you point out, many automotive store sealants contain acetic acid.  GE Silicone II is an example of a silicone sealant product that is readily available at the hardware store (in North America) and avoids the use of acetic acid.  Instead it uses ammonia for curing the sealant, which is not long term harmful to the electronics. Sensor safe silicons should also be ones that avoid the use of acetic acid. Luckily, there’s an easy test to see if your particular brand of silicon produces acetic acid while curing. Just squeeze a bit of silicon on a piece of scrap, and if it smells like vinegar after a while, don’t use it.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

Beamer

Beamer
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Gold member
Thanks for adding that comment Rob. For me acetic acid means ( white ) vinegar but this may not be obvious to others.

Another possibility is to use polyurethane mastic but this is a lot stronger than silicone, so should be applied sparingly, otherwise next time it may be hard to get the lid off.

I would suggest running bead  around the groove in the lid and wiping it off so that the groove is not quite full. This will ensure a good all round seal, without too much extra contact area on the inside rim which will need a lot of force to remove.

    

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