The engineThe crankcase is from a CB550 with its crank but i have adapted the con rods of the CB650.
Also the cylinder and the head are from CB650. Cylinder is shortened and sleeves from CB750 (SOHC)
are in them. The pistons are from CB750 (DOHC) and have an OD of 62mm. So the engine comes up to 612 ccm.
It is build in a complete clutch of the CB650 with its primary drive gears.
Here the part especialy to Paulages : The clutch cover is welded from two parts,
one with the kicker hole from CB500/550 and the bigger part of a CB650 clutch cover.
I also have adapted some parts of the CB650 gearshift linkage (the gearshift spindle arms and stopper arms and so on).
CB650 oil pan, oil pump, primary damper assembly, primary chain tensioner and cam chain tensioner (mod) are also adapted.
The head is welded up in the edges of the valve spring chambers to fit the head cover of the CB500/550.
Head is also heavy ported to match some Keihin CR33 and 35 ID headers. I use the stock valves but lightened and
stock springs and retainers. The cam is regrinded to an ANDREWS profil. But i don´t know more details because its
done by a machinist who is known by a friend of mine. And shame on me i haven´t measured it until yet.
I droped it into the head and it works really well. When i had turned and milled the pistons, i have it done for a
realy beasty Yoshimura cam. The valve pockets are deep enough for everything i think.
Actually the carbs are Keihin CR31 and not CR33. But i have drove them and they worked.
The
Compression
Ratio should be
10.8 to
11.0 . I don´t know the actually correct number
because the first build up of the engine lies back in the early ninetieths.
In May 2006 the upper surface of the cylinder was milled a little bit down.
When i ported the head i measured all intake and exhaust tracts to get the same volume at each one.
Of course the same i have done to the combustion chambers. There will be a nummber of ratio between the volume
of stroke and intake which changes with the target of power peak and revolutions. For good torque the volume
of intake should be larger. If i remember right i have a ratio of 1 : 1.5 or something like this.
By the way the ducts are not polished, only grinded with 120 sandpapers on a flexible spindel at high rpm.
Regards,