Cylinder bk 350 - whether converted?

Hello All,

I am owner of MZ BK 350, and currently start with renovation of it. Previous owners, installed not original engine heads, and I suspect that converted cilinders. Can you look on picture and give me your opinion, whether the cilinders are orginal or after some modyfications. If I am right the cylinder surface touching to engine head should be flat.
Thanksm in advance for your opinion.

Dateianhänge

Hallo an alle - ich habe eine Mz BK 350 und fange gerade mit der Wiederherstellung an. Der Vorbesitzer verwendete nicht originale Zylinderkoepfe, und vermutlich auch geaenderte Zylinder. Koennt ihr euch bitte die Bilder anschauen und mir eure Meinung bezueglich der Originalitaet oder eventueller Modifikationen geben. Muss es nicht so sein, dass Zylinderflaeche zu den Koepfen flach ist?

Vielen Dank schonmal fuer eure Meinungen.

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Habs mal uebersetzt. max ~:)

Yes, there should be no groove. They are flat. Both head and cylinders. Unless it's a 15hp version - there is also no gasket. On 17hp you just plane them with sandpaper on a glas plate and they won't blow (tighten them with a torque wrench) ...

As far as I can see you yould have the 17hp cylinders - so no gasket.

Can you post a picture of the heads?

Thanks for answer.
So if I good understand, the groove 1 on surface 2 is not original, and the area 3 is as should be, mean around 2 mm below surface 2. If I am honest I thought that surface 3 was milled out on lathe by previus owner. All picture of cylinder I found in web, show that there is one level of surface, no any steps.
What paper gradation to use, and how many Nm. when tightening the head.

On picture you can see head which was installed till now (it is probability head from polish motorbike WSK 175, after cutting the cooling ribs ) , and two picture of head which I plan to assembly.

Thanks for any information
Best regards

Dateianhänge

The first head (2nd picture) is something odd

the 2nd one is a 57/58 Modell (would have to check which year they changed that) with the big fins and matches your 1957 model.
Just plane the sealing surface using wet sandpaper on a glas plate. The grating should be not too rough - like 600 ... 1000. Just do a few passes to check if everything is flat.
For the torque: max 15Nm
I usually start at like 5Nm and increase the torque slowly on all bolts equally. If you do it right, there should be no leaks. If it leaks: Do it again and right this time