Abgeschickt von David Paulus am 18 April, 2007 um 03:39:09
Antwort auf: Compression ratio von Matz Rosenquist am 17 April, 2007 um 22:40:51:
: G'evening All!
: I've got this old rundown G/S, the HP(n), and I'm currently trying to find out how to raise the compression ratio. The idea is to raise it to 9,5:1 by either grinding off the head or the cylinder foot by 1,5 mm.
Matz,
If it is an 800 cc engine, you can go to 9.2:1 by selecting the proper BMW pistons. I believe part number 11 25 1 338 020, 021 and 022 are for the Nikasil cylinders. They are for of diameter 84.76, 84.77 and 84.88, repsectively for the bore sizes A, B and C. (Check this before you buy!)
If it is a 1000, use the 1981 and later R100CS pistons for 9.5:1 compression.
I personally do not like shaving until moving beyond what you can get with pistons. If you take too much off you can start having problems with pushrod alignment, valve adjustment, etc.
The source for English language airhead (slang for the 2V Boxers) information is the airheads list,
http://www.micapeak.com/mailman/listinfo/airheads
Especially good on that list are Tom Cutter, Ted Porter, Oak and Robert Fleischer. Tom Cutter worked for Udo Gietl when BMW was racing superbike. (He is doing my shortblock for HPN #420.)
Best regards,
David Paulus
Wauwatosa, WI