Topic: CB500 transmission: intolerable. Fixes? Please help!

[Dreyzar]

Hey guys.
So it seems well documented that the CB500's Achilles heel is the transmission. Even period reviews describe heavy shifting, false neutrals, and even a sticking shift lever on a brand new machine.

This describes my problem VERY well. The shifting would sometimes get so heavy and sticky, it was positively ENRAGING. Neutral could only be found while the motorcycle was moving. If I didn't find it before reaching the stoplight, I'd be obligated to hold the clutch till the light turned green. False neutral could occasionally be found between second and third. It would occasionally slip out of second under power.

All this after replacing the clutch, lifter rod, clutch cable, etc. My clutch was smooth and well adjusted. Servicing the clutch improved the shifting action somewhat, but not much.

My transmission totally blew recently. I was downshifting (too aggresively, I'll admit), heard an odd thunk, and now it won't stay in any gear. Probably broke a shifter fork or something.

I was so fed up with the thing I've let it sit for the past couple months. I was trying to find a 550 motor to swap in, but since I rebuilt the top end just before the tranny blew (didn't even get to break it in), I may as well try rebuilding the thing.

Which brings me to my question: Can the transmission be coaxed into working properly? What were the changes on the 550 that made the action so much better, can they be replicated with the 500? Anyone know any tricks?

Refurbished shifter forks and some undercutting will be a must, but how dramatic a difference can I expect? If a bunch of time and/or money will yield the same inferior transmission, I'll keep looking for a 550 motor.

I've searched but found no specific info on the 500 transmission. Surprising since it seems to be a notorious problem. With so many great 500 builds on here, including some impressive racers, I'm really hoping someone has some experience with this problem!
 
Thanks a bunch.

[thehammer]

you could even use your 500 cylinder block and head on a 550 lower case. I was unaware that 500 trannys where inferior to the 550. I've heard that the only difference between 500s and 550s was engine displacement ? ? ?

[Greggo]

The 500/4 transmissions with the clutch cable entering through the left side had transmissions from the cl360.  The design was old, and the 550's newly engineered setup proved itself superior.

If you choose to stay with the 500 motor, you could have the forks hard welded, and the gears undercut.  There's a guy on the East coast that does it, and members on here have had it done.

[fatmatt650]

I've had similar transmission issues on every SOHC I've owned and period reviews consistently say the same thing. Shift as deliberately as possible and the issues are minimized. Glad to hear you've decided to keep going w/ it. That bikes gonna be sick someday. By the way, my new 550 is purring like a kitten after a proper tune-up and a little carb massage. I hope to have the brakes sorted tomorrow then it's off to DMV. If you're free you should borrow one of mine for "The Ride". Godzilla is coming through next weekendish.

[dave500]

the whole shift design was chaged on the 550,only one fork hangs of the drum,the other two are on their own shaft and pegged to the drum,the counter shaft has a little oil pump on it aswell,the shift drum isnt pegged with that screw and roller thing on the top case it has a ball race on that end instead,you cant put the 550 guts into a 500 case,on the 500 if the shift drum can move sideways because the locator is worn it will trap the shift rod in the upwards position,sometimes you can thin the drum lever so it dosent get trapped and shim the drum locator to better hold it,your trans sounds like these fixes(optomistic at best) are too late,try and find a 550 bottom end or complete motor for the bottom end,youll also need a new clutch cable and the upper rear battery side engine bracket as this holds the 550 clutch outer,and as mentioned reuse your new top end on it,id hate to see you rebuild the 500 tranny and have it do the same.,i have a 500 and a 550,the 500 needs positive deliberate shifts ,the 550 is much slicker.,heres the bracket youll need to slot a 550 straight into your 500 frame,its only for the clutch cable.


im sure ive posted these pictures on this topic before,candidate for faq?this is what you need to fit a 550 motor into a frame with a factory 500 motor,the early 550 was the same frame,this bracket is used on the 550 only frames aswell.

[Scott S]

 Is there any value in 500/550 bottom end parts? My local shop has the remains of a 500 and a 550.  Both have been out in the weather for eons. One of them, the 550 I think, has a gaping hole in the case. If I could get them cheap enough, would there be anything worth salvaging?

[number13]

Have you checked the shifter drum assembly under the clutch basket?
Those can cause all kinds of headaches if the spring breaks.

[Dreyzar]

number 13, I haven't checked the shift drum assembly. All I've done is take apart the bottom end of my parts motor (also with a blown tranny) to see what I'm dealing with. I'll have a look under the clutch in the coming days but I don't expect to get lucky.

Scott, you can't get 500 tranny parts anymore, so new shift forks have some value. I can't imagine though there'd be much worth salvaging from what you describe.

Dave, that's real good info there. Thanks. So the 500 top end bolts right in to the 550 bottom end eh? That seems like the cheaper and smarter option than rebuilding the 500.  Is the ignition the same between the two?

I guess I'm back to looking for a 550 motor.

Still curious to see what exactly blew in the 500 though.

[dave500]

same ignition etc dreyzar,scott s if you can get those trannys cheap theres bound to be a gear or two/forks/shafts,little clips etc,so long as any gear surfaces arent rusted,make like your doing him a favour taking them away.

[Greggo]

I know that the Bike Yard here in the city has a 550 motor available.  It looks pretty crusty, but I bet you could talk them down, because it's been for sale for months.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=360321318644&ssPageName=STRK:MEWAX:IT

[dave500]

low compression on 4?they are all low,at least its got honest readings written on it,if it turns by hand sure.

[KurtK]

I have a put over 12,000 mi on it. Yes it can be a little stickey but never hard to shift.  Never had the transmission apart but something is bent or broken.

[bryanj]

I keep reading on here about bad 500 transmissions, now i have had several and the only problem i have ever found is the clutch operating mechanism and the pushrod getting damaged, especially if teh chain is run loose.

All motor types will break one of everything somewhere in the production run and the 500 is no worse than any other, yes the 550 is improved but then that is evolution more than anything else

[Greggo]

My '71 has 16K miles (only 1200 by me), and for the most part, shifts pretty nicely.  Something tells me that a as a "Semi Geriatric ex-Honda mechanic and MOT tester" you've treated your bikes kindly, and properly maintained them.  I think this is maybe not the case for many PO's.  I can't attest to the condition of the OP's bike, but I have problems getting into first if I go into neutral at a stop.  So, I've gotten into the habit of pushing into first while slowing to a stop.  Staying in gear at lights here where I ride is important anyway, and it's taught in our safety training classes. 

95% of the time, my bike runs great, it's when I'm closer to an oil change I notice the slightly poor shifting/clutching.  So, I'm going to change the oil a bit more frequently than I had, as that makes everything feel much nicer. 

[domer]

my 72 has unknown milage, and i suffer some of the same issues.... finding neutral between 2nd and 3rd, popping out of second during hard acceleration.... but its so few and far between i tend not to worry, but maybe i should?

[Deltarider]

I keep reading on here about bad 500 transmissions...

So do I and every time I'm surprised. I wonder if not merely things (like jumping out of 3rd) are echoed over and over again. I mean my transmisson is untouched since 1976 and has worked flawless in over 130.000 kms. Even the original rod is still in there. Gearshifting up to this day goes like the proverbial knife through the butter. Second clutch cable is still on, but now has become a bit stiff and needs replacement.

[Dreyzar]

Domer, to my understanding, every time the tranny slips out of gear, it round out the dogs on that gear and wears the shifter forks just that little bit more. Basically it keeps getting easier for it to slip out of that gear.Like others have said just shift as deliberately as possible and problems are minimized.

Greggo, I've been looking at that motor. I'm gonna roll over there and check it out when they're open. 

Delta, luck could be a factor. I'm 2 for 2 with bad 500 trannies. The motor that was on my bike when I got it had half the gear teeth missing on first gear, rounded dogs all around and severely worn forks. I got what I was told was a low milage bottom end and built a new top end onto it. The second tranny was always frustrating to say the least, and finally just plain blew.
Its good to hear that some people haven't had problems. This is the info I was looking for in deciding whether to bother rebuilding it. But the 550 trans still seems like a safer bet.



Another question about the 550/500 combo, is the crank the same? Can a 500 top end be installed right on to a 550 bottom end or does the 500 crank have to go in?

[dave500]

same crank.

[Oddjob]

I've got 2 500s both with over 100000 miles on them, one has done 263000 miles, the other has 147,000 miles on it. On both bikes the transmission is original and both still select like a knife in butter, despite the fact the 263000 mile bike was production raced for a couple of years. Both still have the original clutch as well, maybe I've been lucky but I've never had a 500 with a dodgy gearbox, I do have around 5 or 6 gearboxes lying around from bikes I've bought and broken, I've seen selector forks burnt on some bikes, where the selector was wearing against a gear but this was not common.
Also never have a problem selecting neutral, just make sure the gear linkage spring for the neutral selector is fine and that's about it.

[turboguzzi]

30 years ago, my first 500 shifted pretty bad, I had better luck with clutchless shifting rather than with....

my current 500 shifts great, i believe that partly it's because i a used a rearset linkage that gives a better ratio between lever and gearshift rod. i've seen a similar improvement when i changed my VFR's from rod mounted pedal to linkage style

But to be honest, if i had the chance, i'd build a new motor on 550 cases/g'box. much better design with two of the forks running on a separate guide rod

[bryanj]

Now I am Semi Geriatric but when i started with Hondas I wasn't. I spent 3 years running a 500 not changing gear till the rev counter needle came out of the top of the red zone in 1st,2nd and 3rd, that one also had twin discs with one caliper in front and one behind as 550 sliders were not in the UK at the time. Also the clutch always slipped if i took off from a standstil with "Verve" but never gave out on me in all the time i had the bike.

Eventualy i took the top end apart just to have a look and fitted new pattern piston kits and exhaust valves as i was too lazy to clean up the originals(and i got the parts at cost!).

That bike had a Marving 4 into 1 race system on it and I was told that the change down for a corner could be heard 5 miles away.

I agree that a lot depends on the ubiquitous PO and how much of an animal he/she was and that regular servicing/oil changes makes a lot of difference to the life of the bike as well.

[dave500]

i guess some came off the assembly line better than others?a culmination of good tolerance parts against the opposite?i dont mind clutchless upshifts,i avoid it on downshifts though.