I'm curious as to what this would really do

[Oddjob]

I love mucking about, thinking of ways to make the bike both easier to maintain, or to make it handle a little better or go a little faster or even just last a little longer. It's why all of my bikes are modded, not in your face modifications, just little subtle ones that you may not spot until you're up close, most are missed by most unless you're an anorak on the model (guilty there on the 500).

A little example, whilst working at QPM I had to repair a CBX1000 that had had a turbo fitted and the owner had been stupid and turned the boost up above recommended settings, the CBX at the time had only been out for a few months, so little was really known about the engine, the owner wanted a one off, something people would crowd around in the car park, more money than sense kinda guy, so he went down to Dixon Racing and had this huge turbo bolted on, the result was it blew the head off, snapped all the studs, snapped the camchain and blew the head off so hard it dented the underside of the frame. I was given the job of repairing it, which involved a new head etc. It took me a few weeks to do waiting for parts etc, anyway, on completion I bolted the engine back in the frame and was putting the cams etc back in when I noticed something unique about the CBX1000, there are 4 cams not 2. They are joined in the middle by hardened steel crosses, like raised plus signs on each side of a coin of metal. Really odd setup. The more I looked at it the more intrigued I became, you had the ability to reverse one set of cams so that due to the wasted spark system you could have 2 cylinders firing at the same time, 1 and 6, 2 and 5 and 3 and 4. A sort of double 3. All the mechanics came to look at it and we decided to see what it ran like in that configuration. The CBX had only been out a few months as I said so we must have been the first to do this, so I reversed the left hand cams so they matched the right and started it up, it started no problem like that. It did however sound odd, a really odd exhaust note, quite nice actually, I only ran it like that up and down the workshop just to see what it felt like and it felt more powerful but not as smooth as the straight six did. No tank on, just the petrol in the carbs BTW. After that I changed it back and never saw the bike again after it left the workshop. The owner learned his money can't buy everything.

And so I was idling my time thinking of random stuff, and I noticed I have an opportunity to do a mod that whilst others may have done it they've never had the ability to see exactly what they've done in terms of results. In a short time I'll be replacing the clutch damping rubbers in 2 clutch baskets I have, one is a 500 and the other is a 550. It's not well known but the clutches have different gearing between the models, the 500 has 64 teeth on it's rear gear and the 550 has 63, to accommodate this change Honda fitted a different primary drive gear with the 500 having 23T and the 550 24T.

So it's not possible to change the clutch on the 500 to a 550 one without changing the primary drive gear at the same time and of course the 550 clutch is a lot bigger than the 500 is, having a different way of releasing the clutch, the 500 push rod and the 550 cable operated. In the dim and distant past I'd attempted to graft a 550 clutch onto a 500 engine but the clutch casing is slightly different and as a result the engine oil just pours out. I do know someone on the forum has tried this very mod by blocking up the casing alteration to keep the engine oil in place. It should work in theory. But what difference will that make to the engine besides having a lighter clutch that is. Different gearing gives different results, Honda knew this and also altered the gearbox in the 550 so it has different gear ratios for some of the gears, so IF you change the gearing on the clutch but still run the 500 gearbox what difference will this make in real terms?

So what, I was thinking, is what happens IF I fit a 550 rear gear to a 500 clutch basket, in effect retaining the 500 clutch but running the 550 gear ratios, without having to do the casing mod. What result would that give? better top end speed, better acceleration, no appreciable difference, I'm curious.

It would be a simple matter to test the results, notice what speed at what revs the 500 setup gives and after replacing the clutch with the modified basket along with the primary gear run the same test, does it make a difference, and if it does is the difference worthwhile? If it lowers the speed  it's most likely increasing the acceleration, is this something worthwhile? Would it allow the engine to pull to the redline in top for instance, something the 500 won't do unless it's going downhill.

Am I sad to think of stuff like this?

[Laverda Dave]

Well if the engine is apart Ken why not try it and see. Can you fit a CB650 clutch gear to a 500 basket, does it have a higher gear than a 550?  Thinking about it Honda developed the 550 from the 500 and the 650 from the 550 as a last hurrah of the sohc engine so I guess in theory it would be a nice experiment to incorporate all the upgrades from the final variant if there is room to fit them.
What a shame about the CBX, iconic bikes, I'll have a red UK model please👍

[McCabe-Thiele (Ted)]

Would it not be easier to just fit a different set of drive sprockets if you want to alter the acceleration and raise the engine rpm in each gear?

On a Mini Cooper S that had a 3.44:1 final drive as standard you could change it for a variety of different diff ratios going for lower top speed but more accelaration. If you wanted to pull higher top speeds on a well tuned engine you went for a specialist Jack Knight final drive 3.90:1 -  older gearbox casings needed some machining to allow the larger gear to fit.

When I bought my first S a Mk1 it had a really bad gearbox whine at 50 mph  with a notchy gearchange. I could not hear the radio or my passenger talking so I stripped it down. Bearings were all fine - it had been fitted with a competition straight cut gearbox by the PO - I bought it at a closed Auction at Bristol Street Motors in Birmingham so had no history. I soon found out when I looked underneath the vehicle when I saw what looked like corrugated flooring that it had been used for rallying then sold after having an excellent respray in Rootes metallic Kingfisher Blue including the inside of the car.

[K2-K6]

The 24 tooth on drive side will raise the output gearing, less revs per rear wheel revolution.

So gearbox will be going faster for each rpm of crankshaft. Probably accommodated by the increased torque potential of the 550cc

[K2-K6]

CBX camshaft had "Oldham" coupling.

A way of connecting two shaft like that directly to each other, even if those two shaft bores were to be slightly displaced. The joint then just "shuffles" the error without any real affect, as opposed to trying to wear adjacent bearing surfaces to correct itself if was solid shaft.

Would cope with potential machining tolerance if they were there.

[Johnny4428]

Cost of having that turbo fitted + cost of repairs = expensive lesson! 🫣

[Johnwebley]

What a superb thread,

A CBX converted to big bang

Excellent

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[Bryanj]

Ken, the 550 had 3 extra teeth on the rear wheel sprocket to make the overall gearing the same i think

[deltarider]

Ken, the 550 had 3 extra teeth on the rear wheel sprocket to make the overall gearing the same i think

Except for the CB550K3-ED which had 34 teeth like the CB500. In continental Europe that particular K3 model was marketed as the tourer version of the somewhat sportier CB550F2. See the ad below.

[Oddjob]

Well I didn't think this would get a lot of answers if I'm honest, more of the rolling of the eyes and who cares kinda looks.

So lets answer them as posted.

Dave, I don't have a 650 clutch basket, no idea if it uses the same damping arrangement as the 500/550 either, plus I'd have to marry it with it's primary gear and there's a chance the splines may be different to the 500/550 but I do see the point, although if I'm honest I didn't really like the 650 engine very much, not sure why, it got a primary chain tensioner which is very handy (I've got one to fit in my 500), it got rid of the tappet arrangement, again probably better, changed the camchain to a Hyvo one, again, probably better, no points etc, I mean what's not to like, BUT it seemed to lose it's character, it seemed bland. It also didn't really go any better than the 500/550 IIRC.

Yes Ted I could, that's the easy answer BUT my point was would changing just this 2 gears make any appreciable difference, not aiming for more speed etc just curious to see if I can spot any difference between the 2 setups, whilst at the same time not changing anything else, so if I get the same speed with 500rpm less for instance is that a worthwhile mod, I'd personally say no unless you're changing the damping rubbers and you have the other parts handy or can get them real cheap. I'm more curious than anything else, purely from a desire to know point. .

Yes Nige I suspected that, however Honda changed the gears in the 550 box and do those changes negate the clutch gear changes for instance, they only changed a couple of gears but I'm thinking Honda at the time of the 550 were trying to compete with bikes like the RD400 and the Suzuki 550, this I seem to recall was why they changed the gears to get more acceleration, in order to try and compete, which TBH they couldn't, all the 550 could do was to get there without leaving a smoke trail that the police could follow to track you.

I wasn't aware it had a name Nige, nice to know.

I'm sure he regretted having it fitted Johnny, the story goes he was told to keep the waste gate set at 2lbs or something and as soon as he hit the motorway he opened the waste gate screw to get more power. Well that worked, he got more power than he or the motor could handle. 

It was a nice learning curve at the time John, the CBX was so new we didn't even have a workshop manual for it, I had to ring Honda for the torque pressures when I built it back up. Lapping 24 valves in by hand though took me a few days.

Yeah I was aware of that Bryan, I think I'll keep the 34T rear sprocket though, I prefer the speed to the acceleration.

Different markets though Delta, as you point out the K version was made to appeal to touring whereas the F model was made to appeal to the younger crowd, the F looked more modern than the K, although I prefer the look of the 500 over the 550. It has more character.

[Oddjob]

Just checked and the 650 has a 26T primary gear and 61T on the clutch gear. Looks the same so it may be possible. It would depend on the splines matching on the primary gear as Honda did change the primary shaft for the 650. I wonder if anyone has a 650 lump lying about who can check?

[Seabeowner]

I have a spreadsheet with with all the gear ratios for for 500/550.
It's a bit convoluted as was done in fits and starts. Also has a bit added for different tyres.
You can swap around with the ratios.
You may notice that it is set to 36 rear sprocket for 550 as that's on my 550F
The internal gearbox ratios are the same for the 500 and 550.
Just the primary ratio changes from 4.0 to 3.063 and as the final reduction changes from 2.0 to 2.176, so they both come out at a very similar speed at revs.

[SteveD CB500K0]

Isn’t it amazing how the bikes stand up in those old brochures.

Removing the stand in a photo is one click on my phone nowadays.

I wonder how they did it then?


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[andy120t]

I have an old 650 engine if anyone wants to take it away and take it apart to use bits!

[Oddjob]

How complete is it Andy?