Topic: 1981 cb650 cafe build. Need advice

[TPatocka75]

Hey guys,

I'm building a cafe racer out of a 81 cb650. I apologize if this has been discussed before but I can't seem to find any pages so far. The problem is, I want to run a cafe racer style solo seat or build my own. As I'm sure you all know the 81 cb650s have the "drop seat" in the frame making it more of a cruiser style. I was wondering if anyone knew any sites with info on rebuilding the frame so that it is level like the older style cb750s.

Thanks,
Travis

[SOHC4 Cafe Racer Fan]

Travis,

Welcome to the forum.  The 650 is a great powerplant to work with. 

I have seen people cut and modify the 1980-82 CB650 frame rails, but I have not seen any build threads showing it.  I think that is the better route versus mounting tabs for a seat the bridges the gap.  You will probably want to put the frame into a jig to isolate any movement of the other tubes, before cutting the lower rails (rearward of the backbone) and replacing with new tubing.  Make sure that you include a lateral cross-member at the tail end of the top seat frame rails to prevent frame twist when cornering.  Also, you will need to relocate the shock mounts and likely need custom shocks (unless you can duplicate the geometry of a 500/550 frame or a 1979 650 frame.  I wonder if you could cut and graft on a 500/550 rear 1/2 frame to your front. 

Alternatively, you could try to pick up a 1979 650 frame which is much more like the 500/550 frame.

[calj737]

Heck for that matter, Dos has a newly powder coated frame for sale in NJ. Save the work and grab the frame and go on!

[seanbarney41]

These bikes are not that rare and there are tons of swap options.  You will be time and money ahead, and finish with a much nicer final product, to just start with a non-cruiser frame.

[SOHC4 Cafe Racer Fan]

I agree with Cal and Sean.  The best option is to find a 500 or 550 frame and swap in your 650 engine.  The handling on the 500/550 is much better, too.  See if you can find a titled 500/550 frame OR even better a rolling chassis to install the motor into. 

[calj737]

North Essex, NJ
http://forums.sohc4.net/index.php/topic,157475.0.html

[SOHC4 Cafe Racer Fan]

Assuming you don't want to make frame alterations, that's a decent deal for a freshly powdercoated frame. 

[TPatocka75]

Thank you so much for all the replies. I've been on other forums for different projects and never seem to get anyone to answer! That frame sounds like a great deal. Is everything on my 650 transferable? Such as the motor, swing arm, rear hub etc? I'd hate to jump the gun by buying it and not be able to transfer everything or have to buy different parts to make it work.  Thanks again!

[SOHC4 Cafe Racer Fan]

Everything is transferrable from the 650 onto the 500/50 frame. 

The front end is different from the 500/550 -- the 650 has slightly larger diameter fork tubes (better handling) and better brakes.  However the 650 fork tubes may be slightly longer than the 550.  You could lower the forks to match 500-550 geometry by sliding the fork ends above the top triple tree, if necessary.  Your 650 may have air-assist on the forks, which doesn't hold pressure very well.  You could just replace the air caps with standard caps.  Some things to think about.

NOTE: when dropping your 650 engine into the 500/550 frame, you first need to remove the oil pan, oil filter and the top valve covers -- so do not fully fill up with oil before doing this.

[TPatocka75]

so everything is transferable? Including exhaust, carbs, electronics? I'm definitely considering buying that frame it would hate to buy it and then run into issue while trying to swap everything. Are there any pages with more information on making the swap? Like I said this is s build for a friend of mine who's in the navy. He's the one paying for the parts while I build it. I just don't want to waste any time or any of his money.

[SOHC4 Cafe Racer Fan]

You should be able to fit almost everything from the 650 onto the 550 frame.  I'm not sure about the airbox (whether you can use the 650 box, adapt a 550 airbox or go with pods).

You will need to use the 650 electronics, as the 650 uses CDI boxes (and not points).  I think the 650 also came with a solid state reg/rectifier -- an improvement over the 550 components. 

You will also need to use your 650 exhaust, since the exhaust port spacing is different as is the size of the ports.  You can upgrade to a Ripple Rock/Hindle stainless 4-2-1 pipe if you choose.

[calj737]

The only difference in the frame really is the motor mount on the upper right, rear. The 550/650 uses a right side clutch cable with the mount having the retainer channel. The 500 uses a left side clutch. Since you have a 650 frame, just use your mounts in the 500 frame.

[TPatocka75]

Thank you so much everyone for all the great replies. This is a great community!

[SOHC4 Cafe Racer Fan]

I am a little biased but I believe that the 500/550 chassis is one of the most nimble of the single overhead cam four Hondas.  I love my stock 550 but always wished it had more punch.  I explored building a higher performance 550 engine, but since the 650 has more hp and torque right out of the gate and mounts directly into a 500/550 frame, I decided to increase the performance of a 650 motor and use it with a 550 frame.  Several other members have done variations of this type of build.  Some have done what you are contemplating and simply dropped in a stock 650 motor.

[bwaller]

Don, the 650's use 35mm fork tubes same as the 550. They are longer though.

[SOHC4 Cafe Racer Fan]

Don, the 650's use 35mm fork tubes same as the 550. They are longer though.

Thanks, Brent!  I wasn't certain about the diameter, but knew they were longer. 

I think the brakes are better than those on the 550 -- larger pistons, dual disc and aft mounted.

The good news is that you could swap the entire fork over from the 650, adjust the height of the forks (or get new tubes) and use regular fork caps from a 500, 550 or 750 to replace the leaky pressurized air-assist caps.