Re: compression r75/5


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Abgeschickt von Clemens am 08 Februar, 2004 um 15:32:47:

Antwort auf: compression r75/5 von Niels Hansen am 08 Februar, 2004 um 11:30:53:

: Hi. Hope it´s allright Im asking you this question in english. What would the effect of using 900ccm cylinders with the standard 750ccm heads be? Would it mean a considerable increase in compression (due to the smaller hubraum of the 750 heads) or not?

: Thanks

: Niels

Hi Niels,
I don't have an answer to your question but a hint, that may be important.
I know riders who use 900cc or 1000cc cylinders with a /5 engine without
any problems. Additionally I know that the /5 series was planned initially
with 900cc for the top model (a R90/5). Tests showed that the main block
wasn't strong enough for that displacement. It broke in some cases. That is
why BMW decided to limit the displacement to 750cc for the /5 series and
went to 900cc after re-inforcing the block first.
(source of information: German magazine 'mo' Sonderheft BMW-Motorräder,
issue springs 2003).
There's no information concerning what has been re-inforced nor when (during
the production cycle of the /5 or with introduction of the /6 series).
However, if you're using bigger cylinders it might not be the best idea to
raise the compression ratio at the same time. And you surely WILL have a
significantly higher compression when using diam.82 heads on diam.90 cylinders!
Regards,
Clemens


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