Topic: CB 500/650 Tachometer swap.

[Roscoe500four]

*Ok. I've edited the question to try and save confusion.*
I want to put another 650 cam into my 500 Four, but WANT to keep the original gauges.

I know the 500 tachometer gauge doesn't work properly with the 650 drive so my question is:
Will a 650 gauge fit in place of where my current 500 tachometer gauge sits?
Any help appreciated.

[bryanj]

Depends which model 550

[Roscoe500four]

Sorry but there's some confusion.

It's for my 500 Four, that I want to retain the factory tachometer.

My 550 has electronic. It's not the problem.

So again, my question is, will the CB 650 SOHC model tachometer, fit into a 500 Four tachometer holder..

[newday777]

Howdy Ross
When you say the plate, do you mean the chrome bottom trim(#11) of the Tachometer or the black steel plate(#5) the tach bolts to?(see attached fiche)

What month and year was your 500 manufactured (date on steering neck vin plate). There were 2 different size tach/speedometer on the early 500/4, so the chrome bottom trim are different sizes(smaller) if you have the early model.

As to will the 650 fit in the later 500/4 chrome trim,  the year on that 650 tach might also be a factor. I looked at the rubber of the 1979 650 base, it uses the same base rubber(#6) as the later 500/550, 323 center part number. I haven't put a 650 tach in as you are asking for help on, so my point of view is from a parts manager view with numbers. I know of a racer/motor builder friend in California that has built many 650 cam conversion race motors and he shared some stories of the benefits. I'd like to do one myself at some point.

I just did a web search on the cam conversion and this link says you need either a CB650 or a CB750 tach but doesn't mention the mounting.
https://www.chinonthetank.com/2016/05/cb650-cam-in-a-cb550/

[Roscoe500four]

Hi Stu. Thank you very much for that concise answer.
Here's where I'm at. Mine is manufactured in 72 so it's the last model as I understand it. It is a US model (even though I'm in Australia. When I researched my plate, #5, it showed it was the same as other US 500/550 models and the same as the 750 K2-K6. Through reading on here, some (or all, I'm not sure) of the 750 tachometers run the same ratio as the 650.
So now I'm thinking that the 750 fits into the same plate as my 500, if all that makes sense.

I did the 650 cam into my 550, and along with some other mods, it's an absolute flyer. However it has a fairing and went the lazy man's way out with electronic speedo/tachometer.
I'd like to keep the 500 looking as standard as I can..

[bryanj]

Sorry, my mistake i meant 500 as there are two different diameters of clocks and two different types of one size, if you have the K2 model with big clocks then yes the 650 or 750 SHOULD fit but not sure about ratios, yours is not the last year by the way the UK had the 500K1 till 75

[Roscoe500four]

Thanks. Just had someone send me a picture of their 750 tachometer and it turns out its nearly 10mm smaller?

I'm actually thinking of just running a 650 drive to my 500 tacho and see how the whole thing pans out or just not run the drive at all (no tacho).

[Roscoe500four]

FWIW, my tacho measures 97mm OD, at the outer face of the gauge (closest to the rider).
It is a 72 build, American model.

[newday777]

Thanks. Just had someone send me a picture of their 750 tachometer and it turns out its nearly 10mm smaller?

I'm actually thinking of just running a 650 drive to my 500 tacho and see how the whole thing pans out or just not run the drive at all (no tacho).

What year is your 500 manufactured?
You 500 tach has a different ratio and will read much higher than motor is actually turning. That is why you need to swap it.

[Roscoe500four]

Thanks. Just had someone send me a picture of their 750 tachometer and it turns out its nearly 10mm smaller?

I'm actually thinking of just running a 650 drive to my 500 tacho and see how the whole thing pans out or just not run the drive at all (no tacho).

What year is your 500 manufactured?
You 500 tach has a different ratio and will read much higher than motor is actually turning. That is why you need to swap it.

Yes just been doing some more reading and the differences are quite a bit. It might end up launching the needle through the tank!
It's a 1972 build, so 73 model

[newday777]

Then the 73 CB750 tach should fit and look the same and have the correct ratio. Find someone local to you that has 750 parts bikes to verify the fit by taking yours with you. That is the best way.

[Roscoe500four]

Then the 73 CB750 tach should fit and look the same and have the correct ratio. Find someone local to you that has 750 parts bikes to verify the fit by taking yours with you. That is the best way.

Ok. Thanks very much for your help.

[newday777]

If you are near Melbourne, Terry is the one to contact.

http://forums.sohc4.net/index.php?action=profile;u=25

[RAFster122s]

The 650 cam tach drive is a different pitch and must be fitted with the cam in your 500 for your cable drive to work. So, you must fit the cam and the cam tach drive gear from the 650 to have a swap that will work. To avoid having two different sized instruments you could fit a 550 speedo to go with the 750 or 650 tach. The 650 tach has a black face, so cosmetically wouldn’t match.

[Roscoe500four]

The 650 cam tach drive is a different pitch and must be fitted with the cam in your 500 for your cable drive to work. So, you must fit the cam and the cam tach drive gear from the 650 to have a swap that will work. To avoid having two different sized instruments you could fit a 550 speedo to go with the 750 or 650 tach. The 650 tach has a black face, so cosmetically wouldn’t match.

I've come to the understanding that that is the case.

Unfortunately when I built my 500 I had the gauges rebuilt at quite an expense to go with what was a fairly pristine build.
Now I'd have to shell out for two more, most probably have them rebuilt to match the bike, buy the 650 drive and on and on.

I think the easiest and probably most cost-effective way for me to go now, is to send the standard cam from my 550 which is sitting on the shelf here, off to Web Cams, sell the 650 cam to cover some of the expense and when I get the Web cam back simply drop it in without worrying about the whole gauge thing.

Thanks for all your input good people. 👍