A quick look at Siebenrock pistons for a R75/5

These piston and cylinder kits seem to be the rage right now. I used one on the last build and had very little problems aside from the pushrod seals being extremely difficult to install.
The pistons are made to mate with the R75/5 heads and you can use the same carbs (might need to change jetting).

Here is a quick look at the piston and how it compares to a stock R75/5 piston that i have lying around.


It is a lighter, yet wider piston. The piston on the right has the rings on it still. The siebenrock doesn’t have the rings on it.


I didn’t measure heights when i snapped this photo but they seem close.

The piston in the cylinder. The cylinder wall is very thin compared to a R75/5 cylinder.

I haven’t heard of any issues with these yet. Supposedly they give you a 20% gain in power… so that makes it around 900cc.
I’m pretty sure they are cheaper then replacement BMW parts too.

Vapor Blasted heads

Building an airhead BMW that is functional and looks pleasing can be tricky. For example, i got new cylinders from Siebenrock but the aluminum of the clean BMW heads did not match the cylinders.
I thought about different paints and ceramic coatings to use to make them match but the bare aluminum is the most effective way of cooling these machines.

So after some research, i found a place that does Vapor Blasting.
Check out Jeff in Oregon http://www.vaporblasting.biz/index.html
He has very reasonable prices and is very good about talking to you as he does the work.
I sent the heads to Jeff to have blasted. I am VERY pleased with how shiny they came out. It is probably as close as I am going to get to have them match the cylinders.
I’m still thinking of having the heads clear coated with a coating that supposedly does not adversely effect the heat dissipation. I know nothing will be as good as bare aluminum but i am concerned with the long term looks of this bike and after a few thousand miles, i don’t know if the bare aluminum will stay looking so bright unless every fin gets cleaned after every ride…
I used these guys on my last bike and i can say the parts are a joy to clean vs factory BMW aluminum. http://www.xtremeperformanceheatcoatings.com

HeadCylP1010505, siebenrock cylinder and R75/5 head

IMAG0656lr, Vapor Blasted BMW R75/5 head with Siebenrock Cylinder

Not a perfect match… but close enough.

IMAG0657, Vapor Blasted BMW head to match Siebenrock Cylinder