1 Comparo: K75/K100(8V) pistons Wed Jul 04, 2012 2:15 pm
Two Wheels Better
Moderator
Recently I have been pondering the differences between these two model's pistons. The K75 3 cylinder has an 11.0:1 compression ratio whilst the 8 Valve K100 four gets by on a 'mere' 10.2:1. They both use a 67mm bore and 70mm stroke, and share 34mm intake & 30mm exhaust valve diametres.
There is a forum member I know of who is reported to have K75 pistons in his K100 motor with good result. I'm wondering if anyone else out there has experience with this 'upgrade'. Also, has anyone got decent quality photos of a K100's piston top? I'd like to get a visual idea of the differences in valve cut-out area, offset, if any, and squish band, required for valve to piston top clearance.
I fully appreciate that it is a relatively minor 'bump' in compression from stock but it's from little things that big things grow. I went up from 9.5:1 to 10.0:1 pistons on an R100 Airhead and the mid-range to upper RPM 'punch' was quite noticeable, accompanied by cylinder head dual-plugging, an issue not so easily remedied on a K100.
Motobins have these pistons for less than AUD$80 a piece, and you'd then want to use the pinned version of piston rings.
Thinking, just thinking...
Auguste Rodin's The Tinkerer...?
There is a forum member I know of who is reported to have K75 pistons in his K100 motor with good result. I'm wondering if anyone else out there has experience with this 'upgrade'. Also, has anyone got decent quality photos of a K100's piston top? I'd like to get a visual idea of the differences in valve cut-out area, offset, if any, and squish band, required for valve to piston top clearance.
I fully appreciate that it is a relatively minor 'bump' in compression from stock but it's from little things that big things grow. I went up from 9.5:1 to 10.0:1 pistons on an R100 Airhead and the mid-range to upper RPM 'punch' was quite noticeable, accompanied by cylinder head dual-plugging, an issue not so easily remedied on a K100.
Motobins have these pistons for less than AUD$80 a piece, and you'd then want to use the pinned version of piston rings.
Thinking, just thinking...
Auguste Rodin's The Tinkerer...?
Last edited by Guest in the House on Thu Jul 05, 2012 2:03 am; edited 1 time in total
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"A long ride is the answer to a question you will soon forget!" ~ Anonymous
1977 R75/7-100, '93 K11/K12 Big Block, '93 K1100RS, '95 R100 Mystic, '96 K1100RS, 2 x '98 K1200RS, '06 K1200R & '09 K1300GT