Topic: CB550 frame vs CB650 frame

[SOHC4 Cafe Racer Fan]

I recently (today) purchased a CB650 off of CL CHEAP.  My intent was to harvest the motor, rebuild it with a big bore 836 (along the lines of Paulage's build) and drop it into a registered 550 frame -- all the "go" of a 750 motor with the lower weight of a 550.

My question now is whether there are any advantages/disadvantages to using the 650 frame vs. the 550 frame?  Aesthetically, performance-wise?

NOTE: this project will likely include a 2007 GSXR600 front and a boxed swingarm to improve handling.

[calj737]

Why not grab FillionJ's 750 pistons machined for the 550 motor?

To your question, I have no clue. I'd consider the brackets and clearances for rear sets, mufflers and such as the paramount variables.

[bwaller]

I broke a 79 down recently and the wheelbase is a an inch longer. It is somewhat heavier, also has a 27d rake compared to 26 for the 550. I didn't think it was any beefier than a 550 could easily be made to be. Without tying to make the 650 guys angry, I'd say the 650 was originally intended to be more cruiser than street fighter. The 550 chassis should offer lighter steering, probably could be a better sporting chassis. 2 cents worth.......peace!

[SOHC4 Cafe Racer Fan]

Why not grab FillionJ's 750 pistons machined for the 550 motor?

To your question, I have no clue. I'd consider the brackets and clearances for rear sets, mufflers and such as the paramount variables.

Thanks, Cal.  I just sent FillionJ a PM.  This is my ever-evolving second 550 project - to incorporate your swingarm.

[SOHC4 Cafe Racer Fan]

I broke a 79 down recently and the wheelbase is a an inch longer. It is somewhat heavier, also has a 27d rake compared to 26 for the 550. I didn't think it was any beefier than a 550 could easily be made to be. Without tying to make the 650 guys angry, I'd say the 650 was originally intended to be more cruiser than street fighter. The 550 chassis should offer lighter steering, probably could be a better sporting chassis. 2 cents worth.......peace!

Thanks Brent.  This was what I was trying to determine -- which of the two offers better inherent performance, since both frames can accommodate the same engine, front end and swingarm that I have in mind. 

[Tews19]

Drop into a 550 frame! Direct swap and only adds 2 lbs. Cal is correct the 650 is more of a cruiser and Imo does not have the same classic looks of a 550 stance.

[SOHC4 Cafe Racer Fan]

Drop into a 550 frame! Direct swap and only adds 2 lbs. Cal is correct the 650 is more of a cruiser and Imo does not have the same classic looks of a 550 stance.

I'm not certain but the 650 frame seems to have a lower dip in the seat (like a cruiser) vs. the 550 frame.

[Tews19]

Hit up McWilliams or rb550. Both have a few 650s. They can give you the ins and outs.

[SOHC4 Cafe Racer Fan]

Hit up McWilliams or rb550. Both have a few 650s. They can give you the ins and outs.

Will do.  Thanks, Tews!

[Retro Rocket]

I broke a 79 down recently and the wheelbase is a an inch longer. It is somewhat heavier, also has a 27d rake compared to 26 for the 550. I didn't think it was any beefier than a 550 could easily be made to be. Without tying to make the 650 guys angry, I'd say the 650 was originally intended to be more cruiser than street fighter. The 550 chassis should offer lighter steering, probably could be a better sporting chassis. 2 cents worth.......peace!

+1, 650 in a 550 frame....

[reverb]

I have a simular project.
One advantage of the 650 frame is that you can remove a bar from the frame to remove/place the engine.
It seems to me that there is more leg-space in height (standard model not the custom)
Also in a exclusive article about the sohc series it was tested as having the best roadholding qualities.
So I am interrested in other experiences especially if the footpeg-seatheight makes a difference...