Topic: Mismatch cb550 motor in a cb500 bike

[JTknives]

Long story short I scored a cb550 motor to replace my hammered cb500. On a closer look the cb550 motor has a 17T front sprocket but my rear wheel still has the 37T from the CB500. I found a 15T on amazon that someone had for a good price. I grabbed it just incase it would work. Am I head the right direction or should I go a diffrent way. For some reason I thought that the cb550 had a higher tooth count in the rear then the CB500.

[dave500]

the 500 had 17x34 final drive sprockets,the 550 had 17x37 final drive,someone has geared that 500 down by fitting the 37 rear or just didnt know,the 500 and 550 had different internal primary reduction and the rear sprocket change keeps the overall gearing between the two bikes the same,keep your 37 rear and 17 front sprockets itll be correct now.

[bryanj]

You need the 550 right rear mounting plate to fit the 550 into a 500 frame

[dave500]

like so.

[Deltarider]

like so.

Is that the only part you need to get a 550 unit in a CB500 frame?

[bryanj]

Motor yes, carbs and filter box need to be from 500/550 before K3

[Scott S]

like so.

Is that the only part you need to get a 550 unit in a CB500 frame?

 And the matching clutch cable. Some very early 500's had a different plug on the alternator that won't match the 550 wiring harness.

[Deltarider]

Thanks! Good to know.

[dave500]

early 500 connector plugs had small round pins not the flat blade type.

[Scott S]

early 500 connector plugs had small round pins not the flat blade type.

 Yep.... the wiring is the same, just a different plug. The early alternators with the round pins are worth keeping.  Not as many out there and someone with an early bike might need it some day.

[bryanj]

If you got an early round pin generator i need it for my very eary rebuild, cash + postage waiting

[JTknives]

the 500 had 17x34 final drive sprockets,the 550 had 17x37 final drive,someone has geared that 500 down by fitting the 37 rear or just didnt know,the 500 and 550 had different internal primary reduction and the rear sprocket change keeps the overall gearing between the two bikes the same,keep your 37 rear and 17 front sprockets itll be correct now.

I double checked and it is indeed a 34 on the rear. So considering I’m matching a cb550 to it my math says this 15T is a closer fit for proper ratios then if I left the 17T on the cb550 motor.

[Deltarider]

All stock CB550s had front 17 and rear 37. One exception: the CB550K3-ED in Europe had 34 rear (like the CB500 had). This 4-4 CB550K3 model was marketed as the tourer version of the somewhat sportier (4-1) CB550F2 that was also on the market at the time. Cf.:p.62 http://www.honda4fun.com/pdf_parts_list/pdf_spac500-550/CB500-550_K3-K4.pdf

[dave500]

smaller front sprockets pull the chain on a tighter bend,itll work but be slightly lower ratio,good get up n go,less long legs on the highway.

[bryanj]

15 way too small a radius for regular use