Tag Archives: siebenrock

A quick look at Siebenrock pistons for a R75/5

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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.

siebenrock

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.
TopViewSiebenrockC

sideViewSiebenrockC

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

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

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

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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

Before:
HeadCylP1010505, siebenrock cylinder and R75/5 head

AFTER:
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