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I'm missing the upper and lower nut & washer the connects the cylinder head to the cylinder barrel. According to the Haynes manual these are both M10. Do these need to be made of any specific material or can I use a steel M10 washer and nut? See 12 & 13 on attached exploded view. Thank you

I'd go for a structural grade 8.8 nut at least. 1.5mm thread pitch, iirc.
The flat washer used here is quite thick, approx 2.5mm + thick.

Things look a little crusty there, are you going to disassemble and inspect/clean?

No, you can't use stock nuts. The threads are 10mm x 1.5 but the AF (across flats) size is non standard, it's 15mm not the usual 17mm (the same size (but not the same form) as the 4 internal stud nuts). Even if you can get a 17mm nut throught the holes in the fins, you certainly won't get a 17mm socket in to turn it. The washers are also non standard, They are quite narrow and two or three times the thickness of ordinary washers. I don't know why... never really thought about it.

The best bet is to source suitable nuts and washers from an airhead dealer. Not sure where you are in the world but I know they can be obtained at a fairly reasonable price from Moto Bins or Motorworks in the UK.

Rob

Hmmm well, proper nuts and washers from airhead suppliers would be best, but I can fit a 17mm AC nut top and bottom, as well as a 23mm od Sidchrome socket in there.
That's on my '81 so perhaps the earlier models won't fit?

Hey, we're back in business!

Note that if OP is in USA and doesn't have a BMW moto source near him that he can order by part number from the nearest BMW car dealer. The car and bike dealers share the parts network in USA.

I will say that it may take an adventurous parts person. I have one here in melvilleville and will use the car dealer if I can't place a big enough online order to get the free shipping.

My nearest Motorrad dealer is 200 miles away.

ME 109 wrote: ↑Wed Jul 31, 2019 7:02 am Hmmm well, proper nuts and washers from airhead suppliers would be best, but I can fit a 17mm AC nut top and bottom, as well as a 23mm od Sidchrome socket in there.
That's on my '81 so perhaps the earlier models won't fit?

Hey, we're back in business!

OK, I accept what you say. I have found that I do have one 17mm socket (out of five) that is an intereference fit into the hole in the fins. It is 24mm OD and I wouldn't be happy using it to torque the nut because of the intereference between the sides of the hole and the socket. Your socket at 23mm would be a bit happier.

The only other issue, of course, is the annoyance of having to change sockets 5 times as you torque each head up... but that is just an irritation.

So the bottom line is that, if you have a socket with a thin enough wall to fit freely into the hole in the fins (many won't) then it is possible to use a stock nut but the nut used and supplied by BMW is 15mm across flats. According to the BMW electronic catalogue, these nuts are not used anywhere else within the BMW range (bikes and cars) but they are still available under the part number 11 11 1 263 903.

Rob