Author Topic: CB550 with 650 cam - tach issue (Read 3999 times)

CBR1100XXX · « **on:** June 06, 2006, 10:37:53 AM »

I just purchased a 76 CB550 vintage race bike and have a issue with the tach

The bike has a CB650 cam in it and the problem is the tach shows almost twice the rpms it should. At idle it shows 3,000 and rev it up and it runs like 3/4 round the dial.

Is there a different gear ratio on the 650 cam or is there something up with the tach before go out and purchase a new tach

I'd like to sort it out before next weekends race

Any help would br great

Thanks,
Brian

jotor · « **Reply #1 on:** June 06, 2006, 11:59:54 AM »

When I swapped a 650 motor into my 550 I had to use the gages from the 650. I found out later that the tachs are geared differently.

Joe

cb650 · « **Reply #2 on:** June 06, 2006, 03:52:19 PM »

Interesting! Paul brought over a 550 cam and we compaired it to a 650 but never thought to count the drive teeth.

Terry

DammitDan · « **Reply #3 on:** June 07, 2006, 09:00:38 AM »

Are the tachs are geared differently or does the worm gear on the 650 cam have more threads on it?

cb650 · « **Reply #4 on:** June 07, 2006, 01:03:35 PM »

I was thinking today (thats a first) about if its the tack or the drive and not the gears on the cam.

Terry

78 k550 · « **Reply #5 on:** June 07, 2006, 02:59:10 PM »

I thought they looked exactly the same. I would bet it is in the tach. gear.

Paul

cb650 · « **Reply #6 on:** June 07, 2006, 05:01:52 PM »

Quote from: 78 k550 on June 07, 2006, 02:59:10 PM

I thought they looked exactly the same. I would bet it is in the tach. gear.

Paul

Thats that I thought but thinkin gets me in trouble

Terry

jotor · « **Reply #7 on:** June 07, 2006, 08:46:33 PM »

Giving this some more thought

it seems that, since the 550 tach reads too high when driven from the 650 cam in either a 550 or 650 motor, then the tach cable must be spinning faster. It really doesn't matter why, just use a tach from a 650 bike and you will solve the problem.

Or am I missing something?

Joe

DammitDan · « **Reply #8 on:** June 09, 2006, 02:28:32 PM »

Yeah that's an easy way to fix it jotor, but we're tryin to figure out WHY it spins faster! If the cams have the same worm gear, then it's either the driving gear on the head cover or the reading gear inside the tach.

My guess is it's the drive gear on the head cover. You can take those things off, right? Might be cheaper than finding a new (used) tach.

Bodi · « **Reply #9 on:** June 09, 2006, 08:39:43 PM »

It doesn't make sense to me. You have a set of 2 gears, the cam gear and the driven gear in the rocker cover. They have to have the same size and pitch of teeth or they won't mesh. They also have to be sized right - and to get a higher tach drive speed either the cam gear has or be bigger or the driven gear has to be smaller. With the sharp tooth angle on the driven gear this maybe isn't exactly true, the gears could be the same size and get different speeds from a different tooth angle (I think). But the 2 gears would have to match - you couldn't change one gear's tooth angle and have it mesh with the other unchanged one.
I think that for the 550 cover gear to be turned faster by the 650 cam gear one or both must be damaged by having the unmatched gears forced together.

DammitDan · « **Reply #10 on:** June 09, 2006, 08:55:17 PM »

Hmm... I guess the number of threads don't matter if you don't change the thread pitch.

Eh, that's why they call it a guess!

Too bad though, a replacement drive gear would have been a lot cheaper than a new tach.

scunny · « **Reply #11 on:** June 09, 2006, 09:06:09 PM »

my 650 has 10 spiral cut teeth on the drive and 4 spiral cut teeth on the cam, any help ?

CBR1100XXX · « **Reply #12 on:** June 10, 2006, 07:08:34 AM »

My son has a CB500, I think I'll yank his tach and give it a try
I don't have time today but, I will give it a go tomorrow

It would be nice to have a tach on the track next week
I'll keep you posted

Thx Brian

FunJimmy · « **Reply #13 on:** March 10, 2008, 08:16:42 AM »

Brian

If you still have this bike, tell us how well the 650 cam works in a 550.

Thanks
FJ

kayaker43 · « **Reply #14 on:** March 10, 2008, 09:39:44 AM »

There's more chatter on the tach issue here http://forums.sohc4.net/index.php?topic=31810.0

Same thing as always though, theories, guesses, rumors and "'ll get back to you's" but no solid answers. Seems like someone struggles with a problem then posts here for help and once its figured out, never posts the results.

This forum is still a great resource though, more active and knowledgable members than most forums. I've got to believe the answer is in the archives somewhere though.

mark · « **Reply #15 on:** March 10, 2008, 09:53:12 AM »

My spare 550 cam has 3 spiral cut teeth and there are 10 teeth on the driven gear.

Looks like the tach goes with the cam.

Happy trails.

FunJimmy · « **Reply #16 on:** March 10, 2008, 10:07:15 AM »

Quote from: madmark73 on March 10, 2008, 09:53:12 AM

My spare 550 cam has 3 spiral cut teeth and there are 10 teeth on the driven gear.

Looks like the tach goes with the cam.

The 650 cam that I have has 5 spiral cut teeth and there are 10 teeth on the driven gear.
That explains the large difference in readings.

kayaker43 · « **Reply #17 on:** March 10, 2008, 10:17:47 AM »

I agree, to spin the cable faster, the 650 cam has to have a larger diameter gear, or different pitch angle on the teeth. A larger gear wouldn't fit so that means they probaly don't match and the plastic gears is getting chewed up. Probably best to remove it or find the 650 gear?

I would like to know how much improvement the cam makes in a stock motor?

ieism · « **Reply #18 on:** May 04, 2008, 02:07:12 AM »

I would really like to know this too. There's another long tread somewhere that explains how and why it would work, and what fits and what doesn't .
I'm not interested in how well it fits, i'll make it fit. I don't care if the tach if off either, i'll get another one.

WHAT I NEED TO KNOW: Does this make an improvement in performance over the 550 cam? Are you guys running a stock or ported engine with it?
I'm in Europe, so getting a hot cam here is impossible. Sending a cam over to get it done is too expensive for me.
Dropping in a 650 Cam would be ideal, but I need to know if it makes an improvement before I spend money on a cam and new gaskets.

Ivar

Rod · « **Reply #19 on:** May 04, 2008, 04:22:00 AM »

Quote from: ieism on May 04, 2008, 02:07:12 AM

I'm in Europe, so getting a hot cam here is impossible.

Ivar

Hi Ivar - there is no problem getting hot street or full race profiles for the 500/550 here in the UK, if you want details let me know.
Rod

ieism · « **Reply #20 on:** May 04, 2008, 05:05:36 AM »

PM send,

Still, a 650 cam would be much cheaper....

hymodyne · « **Reply #21 on:** May 04, 2008, 11:51:08 AM »

I'm in the process of installing a 650 cam in a 550 head right now. I've had to bevel the sides of the head where the clearances were too tight, I'll have to do the same on the cam cover as well. As far as the tach, I switched to a 650 cable and drive gear, as well as tach and speedo from a 650.

I'll let you know how it comes out. I'm taking pictures for a possible article later.

hym

Muk · « **Reply #22 on:** May 07, 2008, 12:13:54 PM »

Did anyone find out if the 650 cam makes a performance gain on the 550?

ieism · « **Reply #23 on:** May 07, 2008, 01:02:01 PM »

One of you guys gave me adresses for cams in the UK, I called but they are too expensive for me now. Thanks anyway.
The man that's porting my head has some experience using 650 cams, I'll ask him when my head is finished, but that could take a while.

Ivar

HondaMan · « **Reply #24 on:** February 19, 2009, 04:59:25 PM »

Quote from: hymodyne on May 04, 2008, 11:51:08 AM

I'm in the process of installing a 650 cam in a 550 head right now. I've had to bevel the sides of the head where the clearances were too tight, I'll have to do the same on the cam cover as well. As far as the tach, I switched to a 650 cable and drive gear, as well as tach and speedo from a 650.

I'll let you know how it comes out. I'm taking pictures for a possible article later.

hym

Drool...

Did you ever get this done, Hymodyne?

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Author Topic: CB550 with 650 cam - tach issue (Read 3999 times)

CBR1100XXX

CBR1100XXX