TT so from the numbers it is a 550 engine with the sprocket cover from a 500. Why would someone do this switch, can that be done putting a 500 clutch cable on the sprocket side of a 550?
22a carbs would be right for the 1974 cb550
I was thinking this morning that something happened to the 550 engine and they put a 500 engine in easy swap but wouldnt they have to put the top part of the case on the 500 engine to get the 550 serial number plate that seems like a lot of work and for what.
Everything about the bike says 74 CB550... Except the clutch. It's very peculiar. The 550 model was introduced to cure some issues with the clutch and shifter mechanism. There was also a trochoid pump to improve lube of the trans parts added to the 550. (HSM Chapter 9.)
If it were a Cb500K2 bottom, the shifter mechanism would also be different, and to the left of the serial number plate will be a shift drum guide screw (Honda shop manual chapter 4, pg 43, fig 123) that the Cb550s don't have. Your posted pictures did not encompass that area for scrutiny.
Chapter 9 of the Honda shop manual describes the changes from Cb500 to Cb550. Your bike may be living proof that the CB500 clutch, it's cover, and actuator mechanisms can be retrofit onto the Cb550 lower end. Notice you still have the cable perch on the right side of the bike, as a CB550 should have.
The reasons why someone would actually want to do this escapes me, as these parts were considered inadequate after introduction to the market, hence the redesign.
Some of the CB500s with clutch issues (slippage/excessive drag) were field modified with aftermarket heavy duty items. The Cb500 clutch was sensitive to adjust, the sweet spot between getting minimal slippage AND full Clutch disengagement escaped many. If the adjustment was biased toward no slipping, then clutch drag made the shifter mechanism wear faster and parts would break. But, until it broke this was preferred to clutch slippage by the rider. Honda did many shop repairs to the CB500 transmission, according to my Honda mechs who worked them in that era.
There were so many warranty repairs, that Honda wanted to eliminate that with the Cb550 model transition. There was also the clutch actuator rod that wore quickly and often broke in many pieces, which made actuation and adjustment even more problematic.
Speculation:
Maybe your bike has some heavy duty items in the clutch pack as "insurance" that the clutch wouldn't slip? These parts may have been new parts/race prats that were on hand when the 550 was acquired?
Maybe it was a parts convenience modification. Why buy a new clutch with this wrecked donor bike sitting next to it?
I would seek out the newer clutch pieces to restore it, as the HD 500 Clutch mod with it's stiffer springs, can fatigue the clutch hand rather quickly. The stiffer springs also contributes to "lazy" or only partial clutch disengagement, which serves to increase wear on the shifter forks and entire shifter mechanism. Those parts are much harder to replace than the clutch pieces.
