Topic: CB550 - CB650 interchangability

[bill440cars]

go for it,i would love to hear about it.

I'd be all over it if I had more than $0.27 in my bank account.

                    I've got you beat, I've got $0.48 in mine. I feel your pain, I really do. Come on Pay Day!

                                                  Later on, Bill

[paulages]

i'll gladly be a guinea pig for trying this stuff, if you guys will help me with the tech stuff...

i'm sure i can turn up a 650 motor here in portland...now if i can only find all of the aftermarket parts to go for a bigger bore.

[mlinder]

i'll gladly be a guinea pig for trying this stuff, if you guys will help me with the tech stuff...

i'm sure i can turn up a 650 motor here in portland...now if i can only find all of the aftermarket parts to go for a bigger bore.

750 pistons have been fit to 550's, if I remember reading that correctly. Dunno how reliable that would be though. Make you way oversquare.

[paulages]

i'm thinking of trying the overbored 650 in a 550 route. gotta have the kickstart, and i really like the idea of a hidden beast in such an innocent looking engine.

[bill440cars]

i'm thinking of trying the overbored 650 in a 550 route. gotta have the kickstart, and i really like the idea of a hidden beast in such an innocent looking engine.

               My thoughts exactly. I've always like the "Sleeper" image. I know it wouldn't be the same as
    the High Tech Sport Bike, but still I think it be pretty interesting. I'll be keeping my eyes & ears
    open  to see what comes out of this! If anyone gets going on this, details and pictures please.

                                                             Later on, Bill

[Tim.]

It seems the main thrust of this thread has been modifying a 550 with 650 bits, but I'm still interested in hearing about the total swap idea and how complex it is to put a complete 650 engine into a 550 frame.

Do the motor mounts and everything line up?  Wiring issues?  I understand the exhaust would be different, but would really like to know if it is truly just a bolt-in change or if it's more complicated.  I might have access to a nice 650 engine for a good price that would be a nice change from my lemon of a 550 engine.

[kayaker43]

The 650 drops right in. You will lose the kickstart, but the exhaust should bolt right up. I would use the old cb550 dyno and ignition system to avoid major wiring. The 650 generator is less reliable anyway. Use the 650 carbs of course. Very easy swap.

[Ibsen]

I would use the 650 ignition system, even if it requires some wiring. Then you won't have to mess with points and timing adjustments.

[Pinhead]

The 650 drops right in. You will lose the kickstart, but the exhaust should bolt right up. I would use the old cb550 dyno and ignition system to avoid major wiring. The 650 generator is less reliable anyway. Use the 650 carbs of course. Very easy swap.

Reading this leads me to believe you can put a 550 alternator/charging system in a 650. Obviously I would have to change the rotor and regulator. How about the stator?

[kayaker43]

The 650 cases and crank end are the same, you would have to change everything else including the cover, plus of course the regulator/rectifier and any wiring changes.

My plan is to use all the external covers from a 500 on a 650 engine to preserve the vintage look. That means running the 500 charging system. Either ignition system will work but I'll use the old chrome points cover. The old cam cover will also work even thought the gasket sealing areas are different, apparently there's enough overlap for a seal. Not sure about the clutch cover yet, maybe the older ones will work but may have to change clutches too, and then there's the no kickstart issue on 650's. The old sprocket and starter covers should work.

A sharp eye will pick out the differences in cylinder and head fin shapes as well as lack of separate intake manifolds on the 650. I suppose you could trim the 650 fins to look like the 500?

[paulages]

is the 650 gearbox so different that it couldn't be modified to accept the 550 kickstart and clutchcover? i really know nothing about the 650 engine layout...

[Pinhead]

I think I would rather have the clutch from the 650 than the kickstart from the 550. So many people say the clutch on the 650 is a huge improvement.

[paulages]

honestly, i seldom ever use the kickstart on my 550, because on the F model you have to actually move the footpeg out of the way, move the arm out, then start it. electric start works every time, i just like the idea of having it as a backup. pushstarting is no fun.

[bill440cars]

I think I would rather have the clutch from the 650 than the kickstart from the 550. So many people say the clutch on the 650 is a huge improvement.

                 I thought I'd kept up with the 500/550/650 thing pretty good and while I remember hearing that the clutch on the 550 was better than the early 500, I hadn't heard that the 650 clutch was even better. Is this really so or has pinhead gotten slightly confused withe the 500/550 clutch thing. Could somebody please clarify? Myself, I've got a 73' CB500K, 2 CB500 motors (gotta check serial numbers to determine year models), a 77' CB550K and a 78' CB550K. I thought all except maybe the 2 motors had good clutches for sure. 

                                                 Later on, Bill     

[kayaker43]

Not sure about actual clutch construction, but the 650 primary drive ratio was changed to lessen the torque the clutch and transmission see. Even a 550 clutch would handle more torque this way. It was a clever way to use an existing clutch/transmission design but enable it to handle additional horsepower. The clutch see's the same hosepower but spins faster at lower torque. The final drive gearing is then adjusted to get the proper road speed.

The same principle behind snowmobile brakes. One tiny disc spinning really fast with less torque can stop a big sled ecause its force is multiplied by the gearing.

I think the big improvement in 500 vs 550 clutches came when they moved the actuation to the clutch side. The 500 used a long pushrod from the left side and it was prone expansion with heat and using up the lever freeplay?

[bill440cars]

      kayaker,
         Thank you, that info may have been put out elsewhere but, If It was, I didn't see it. Appreciate
   the info. I've got a better understanding now. And because of the differences between the 550
   and the 650, I bet the 650 trans along with the clutch could be adapted to go in the 550 case,
   huh? I'm keeping close tabs on this subject, cause someday I'd like to build a 650 disguised as a 550
   and cause a little disruption, if you know what I mean? Shame we can't get all the technical info, on
   this subject documented and put where we could easily refer back now and then, as we need to.
 

                                                       Later on, Bill

[Pinhead]

One of the more pesky problems associated with hot-rodded engines is the increased strain on all the hardware between crank and rear wheel. Honda's solutions to the problems are clever and numerous. The first is an oil feed pipe aimed right at the Hy-Vo type chain connecting the crank and primary-drive jack-shaft, which insures that the chain isn't going to fail for lack of lubrication. They lightened the load on the clutch by reducing the primary reduction ratio, trading a higher clutch speed for lower torque applied at the clutch plates. It's not the first time they've employed the same expedient. The original CB500's 3.25:1 primary ratio became 3.06:1 in the CB550, and now has been revised to 2.74:1.

The CB650's clutch performed in a manner beyond serious reproach. It had a little cold-oil drag on its first use in the chill of the morning, enough to get a clunk out of the shift into low gear and a forward lurch of perhaps an inch. Apart from that, the clutch was perfect. Honda built a new kind of low-friction release mechanism into the cover, the clutch springs are extremely light, and just one middling-strong finger can supply enough pressure to pull the lever right back against the handlebar grip. Best of all (especially for inexperienced riders), the clutch engages ever so gently, with a broad range of lever movement from first contact to full grip. It is a world easier to cope with than some of the toggle-switch clutches some motorcycles still have.

from http://sohc4.us/650/articles/79650rt

[scunny]

thanks for that article Doug, I thought my clutch felt too light, and after pulling the motor apart, I couldn't see anything wrong there.

[paulages]

are the intake runners interchangable from the head, as with the pre/post 1977 cb550 intake differences, or are the mounting studs and all different? in other words, could an '82 head be made to work with '79 carbs?

[Ibsen]

There are no mounting studs for the intake manifolds. They are held in place with a clamp on each end. And no, according to those who have tried, the earlier carbs will not fit the 82 model head. The spacing between the intake ports are different since the 82 model had the larger CV carbs, which also required  different sized intake manifolds.

[bryanj]

One of the 650's, sorry cant remember which, had the inlet stubs cast into the head not bolted on

[Ibsen]

One of the 650's, sorry cant remember which, had the inlet stubs cast into the head not bolted on

All the SOHC 650 have the stubs casted into the head, and with rubber manifolds clamped on them, whilst the DOHC 650 have them bolted to the head.
But there is a difference in the spacing  between the casted stubs on the SOHC 650 cylinder heads used for the PD carbs and the CV carbs. Also the distance between the centre of the stubs for cylinder 1 and 4 are different.

[kayaker43]

The earlier CB650, 79/80 heads use the 500/550/750 carb spacing. Does anyone know what other carbs will fit the 81/82 heads. There must be some other bike that shares the same spacing? I wish I had access to a salvage yard for answers like this???

[Pinhead]

The earlier CB650, 79/80 heads use the 500/550/750 carb spacing. Does anyone know what other carbs will fit the 81/82 heads. There must be some other bike that shares the same spacing?

When I first started searching for parts for the '79 650 I thought I had gotten the wrong bike. I could find parts for the newer stuff, but not the 79. Now it's starting to look brighter. If I can swap parts off other bikes, parts are even more common for the '79 than the later models!

I wish I had access to a salvage yard for answers like this???

Me, too! I'm going to call Oz Cycle Salvage to ask them if I could rummage through their yard just to compare stuff. They usually don't let people in, they just pull the parts themselves and then sell them for outlandishly high prices. Maybe I could get in if I tell them what parts they can "brand" for different bikes (and thus give them a wider customer base).

[markymark]

Ok i'm now confused about all this carb talk.  I have a 76' cb550 that I am running cb750 carbs on(kehein).  So I think I went from a 24mm carb to a 28 or 29mm carb.   So my question is this, if I put a cb650 into my bike, why can't I use the same 750 carbs on this cb650?  PLEASE HELP.  Why do I have to get different carbs?  More air, more fuel, more fire, more power:).