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R90S head chamber volume

The place to discuss the R 90 S as well as the R90S Worldnet archives!
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JCWorks
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Joined: Thu Nov 25, 2021 8:41 am
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R90S head chamber volume

Post by JCWorks »

Hi!

I had a smoking issue on my 1975 R90S, dismantled the head and cylinder and realized rings were shot. So the smoking issue would be easily cured. I thought... at first.

Then I had a closer look at the cylinder head and gasket. The gasket was a 2.75 mm copper decompression plate and the cylinder head had been milled basically flat. Original owner was a well known race guy, so he probably did some work on the engine, including dual plugs. Then another guy kind-of rebuilt the engine and probably wanted it back to original spec without having to spend a fortune on original-spec heads. Well, that was background.... Now the issue:

Does anyone here know the chamber volume of an orginal R90S-head? I would like to do some maths to make sure I get the compression ratio correct.


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srankin
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Re: R90S head chamber volume

Post by srankin »

JC, if you don't get an answer here in the Vintage club, try some of the other clubs on the web.

Meanwhile I will ask my AU R90 expert if he knows. Good luck St.
Owner of a 84, R80RT and 78, R100RS

JCWorks
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Re: R90S head chamber volume

Post by JCWorks »

Thank you, Srankin. I´m not really that good with forums so if anybody has a suggestion where to find a good source for R90S-info, I´d be listening :)

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srankin
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Re: R90S head chamber volume

Post by srankin »

Sadly JC a lot of the old R90S sources are going away. My friend in AU ran a website for years until his last accident.

He did not know the answer to your question but suggested you contact Tom Cutter at Rubber Chicken Racing.
http://www.rubberchickenracinggarage.com

The only other source might be SnowBum who is a contributor to the Vintage BMW Motorcycle Owners.

Good luck St.
Owner of a 84, R80RT and 78, R100RS

bmstan
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Joined: Sat Nov 05, 2022 7:58 am
Location: UK

Re: R90S head chamber volume

Post by bmstan »

My 1975 R90s with a plug fitted to a clean head, no carbon, is 87cc level to the head gasket face.

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