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Author Topic: CB550 Reseal and 650 Cam Swap  (Read 3208 times)

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Offline JLeather

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CB550 Reseal and 650 Cam Swap
« on: March 19, 2021, 06:44:53 AM »
Well, as with everyone else my CB550 oil 'seepage' has gotten to the tipping point.  Time for a reseal of the topend.  Already replaced the o-rings at the ends of the cam (no help) and when I pulled the v/c there was no oil under the pucks so that pretty much left headgasket.  Engine has never been apart since new.  I've also got a CB650 cam and tach drive so...  This thread is part motivation, part place for me to ask questions.  From what I gather there is not any required jetting changes when going to a CB650 cam?  Also can anyone comment on the quality of the 4into1.com top end gasket set?  I have several of the gaskets I need left over from other engine rebuilds so I'm tempted to buy just what I need.  Does anyone have the sizes for the necessary o-rings (base, supply, and cam cover ends) that I can just source in Viton?
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Offline Ryan66

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Re: CB550 Reseal and 650 Cam Swap
« Reply #1 on: March 19, 2021, 08:39:31 AM »
Youll need the 650 tach cable and a 650 or 750 tach. I literally just got my tach yesterday for the same swap. Curious on the gasket sets as well. Currently tearing down my motor to inspect and replace all necessary gaskets.
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Offline caluser2000

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Re: CB550 Reseal and 650 Cam Swap
« Reply #2 on: March 26, 2021, 10:34:13 PM »
CB650 and CB750 tachos  are different ratios.

https://mostynindustries.com.au/speedo-tacho-ratios
« Last Edit: March 26, 2021, 10:37:28 PM by caluser2000 »
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Offline Ryan66

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Re: CB550 Reseal and 650 Cam Swap
« Reply #3 on: March 27, 2021, 06:26:50 AM »
Quote from: caluser2000 on March 26, 2021, 10:34:13 PM
CB650 and CB750 tachos  are different ratios.

https://mostynindustries.com.au/speedo-tacho-ratios
I read somewhere that some year 750s have the same ratio? I took that issue out of the equaiton and found a clean 650 tach just to keep it matching.
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Offline Scott S

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Re: CB550 Reseal and 650 Cam Swap
« Reply #4 on: March 27, 2021, 07:02:01 AM »
Quote from: Ryan66 on March 19, 2021, 08:39:31 AM
Youll need the 650 tach cable and a 650 or 750 tach. I literally just got my tach yesterday for the same swap. Curious on the gasket sets as well. Currently tearing down my motor to inspect and replace all necessary gaskets.

 The 550 cable will work fine. You need the 650 tach DRIVE.
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Offline Ryan66

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Re: CB550 Reseal and 650 Cam Swap
« Reply #5 on: March 27, 2021, 08:18:29 AM »
Quote from: Scott S on March 27, 2021, 07:02:01 AM
Quote from: Ryan66 on March 19, 2021, 08:39:31 AM
Youll need the 650 tach cable and a 650 or 750 tach. I literally just got my tach yesterday for the same swap. Curious on the gasket sets as well. Currently tearing down my motor to inspect and replace all necessary gaskets.

 The 550 cable will work fine. You need the 650 tach DRIVE.
I was referring to the actual tach. Has to match the ratio of the tach drive.  Yes the 550 cable will work with the 650 tach drive.
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Offline caluser2000

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Re: CB550 Reseal and 650 Cam Swap
« Reply #6 on: March 27, 2021, 09:54:40 AM »
Quote from: Ryan66 on March 27, 2021, 06:26:50 AM
Quote from: caluser2000 on March 26, 2021, 10:34:13 PM
CB650 and CB750 tachos  are different ratios.

https://mostynindustries.com.au/speedo-tacho-ratios
I read somewhere that some year 750s have the same ratio? I took that issue out of the equaiton and found a clean 650 tach just to keep it matching.
No,not at  all...
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Offline Alan F.

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Re: CB550 Reseal and 650 Cam Swap
« Reply #7 on: March 27, 2021, 10:02:09 AM »
Is this cam swap applicable to 500 models or just 550s?
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Offline Scott S

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Re: CB550 Reseal and 650 Cam Swap
« Reply #8 on: March 27, 2021, 01:17:22 PM »
500 and 550. Lay the cam in the head and turn it by hand. Make sure the lobes clear the head. Some clear fine, sometimes you need to remove a little material on the head.
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Online bryanj

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Re: CB550 Reseal and 650 Cam Swap
« Reply #9 on: March 27, 2021, 01:54:49 PM »
500 and 550 heads are identical
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Offline caluser2000

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Re: CB550 Reseal and 650 Cam Swap
« Reply #10 on: March 27, 2021, 02:03:15 PM »
Quote from: bryanj on March 27, 2021, 01:54:49 PM
500 and 550 heads are identical
they certainly are. As are the components in them-valves, valve guides, valve springs etc.

Though different part nos. CB500/4 carb banks will work with pre '77 CB550 engine setups as well. They are setup a bit richer though.
« Last Edit: March 27, 2021, 02:08:38 PM by caluser2000 »
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Offline Alan F.

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Re: CB550 Reseal and 650 Cam Swap
« Reply #11 on: March 27, 2021, 03:38:14 PM »
Thanks gents, I'd have guessed so but I'm a 750 guy and mostly illiterate about 500/550/650 but learning some things along the way.
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Offline caluser2000

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Re: CB550 Reseal and 650 Cam Swap
« Reply #12 on: March 27, 2021, 04:28:16 PM »
Quote from: Alan F. on March 27, 2021, 03:38:14 PM
Thanks gents, I'd have guessed so but I'm a 750 guy and mostly illiterate about 500/550/650 but learning some things along the way.
They are great bikes to ride in the tighter roads. Just play a tune on the gear box and you are sweeeet! :)
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Offline JLeather

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Re: CB550 Reseal and 650 Cam Swap
« Reply #13 on: April 01, 2021, 08:28:54 AM »
I've got several CB750 tachs kicking around, and I've got the 650 tach drive.  Hit a small snag on my reseal.  The front/right stud seems to have trapped some water at some time and gotten pitted.  I'm not confident it'll handle a retorque.  I don't have any spare 550 motors or studs, but I've got quite a few 750 parts motors.  Anyone know if one of the studs in a 750 is the same size as a 550 front (short) stud?  Failing that I'm in the market for one good used stud.  Not looking to spend a hundred bucks on an HD set...
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Offline JLeather

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Re: CB550 Reseal and 650 Cam Swap
« Reply #14 on: April 01, 2021, 08:30:32 AM »
Quote from: Scott S on March 27, 2021, 01:17:22 PM
500 and 550. Lay the cam in the head and turn it by hand. Make sure the lobes clear the head. Some clear fine, sometimes you need to remove a little material on the head.

Good to know.  I'll have to check that out before I get any farther.
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Offline caluser2000

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Re: CB550 Reseal and 650 Cam Swap
« Reply #15 on: April 01, 2021, 09:44:57 AM »
750 and 650 tachos are different ratios:

https://mostynindustries.com.au/speedo-tacho-ratios

650/550s/500s are 7:1

750s are 4:1

« Last Edit: April 01, 2021, 09:56:42 AM by caluser2000 »
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Offline JLeather

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Re: CB550 Reseal and 650 Cam Swap
« Reply #16 on: April 01, 2021, 09:58:59 AM »
I believe that site is incorrect regarding the 650 tach ratio.  This is excerpted from the forum FAQ:

CB750 Speedo  2240:60  Tach 4:1
CB650 Speedo  2240:60  Tach 4:1
CB550 Speedo  2240:60  Tach 20:3
CB500 Speedo  2240:60  Tach 20:3
CB400 Speedo  2240:60  Tach 20:3
CB350 Speedo  2240:60  Tach 20:3

This is bolstered by the experience of others who've done the 650 cam swap and had to change tachs.

EDIT - I've not yet done either of the above yet...  I'd be quite happy if my 550 tach works as it's in better shape (and matching) as compared to the 750 tachs I've got.
« Last Edit: April 01, 2021, 10:01:31 AM by JLeather »
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Offline caluser2000

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Re: CB550 Reseal and 650 Cam Swap
« Reply #17 on: April 01, 2021, 10:02:52 AM »
Quote from: JLeather on April 01, 2021, 09:58:59 AM
I believe that site is incorrect regarding the 650 tach ratio.  This is excerpted from the forum FAQ:

CB750 Speedo  2240:60  Tach 4:1
CB650 Speedo  2240:60  Tach 4:1
CB550 Speedo  2240:60  Tach 20:3
CB500 Speedo  2240:60  Tach 20:3
CB400 Speedo  2240:60  Tach 20:3
CB350 Speedo  2240:60  Tach 20:3

This is bolstered by the experience of others who've done the 650 cam swap and had to change tachs.

EDIT - I've not yet done either of the above yet...  I'd be quite happy if my 550 tach works as it's in better shape (and matching) as compared to the 750 tachs I've got.
Thank you for that info.

http://forums.sohc4.net/index.php?topic=41940.0

 "The tacho is 20:3 or 6.67. The 350/400/500/550 are all the same. The CB750 is 4:1"

So looks like 7:1 is close enough it seems. 6% or so difference.

The 650 tacho is still drivenby the cam though isn't it? And based on the CB550 engine. Its a long time since I had my 650 Custom.


IIRC other components such as the rocker box assy. complete with rocker arms. Apart from the capacity change, HiVo cam chain and primary chain spring loaded adjuster to stop damage to the oil filter gallery at the bottom of the crank case it's effectively the same engine as the CB550s.Shares the same gear box lay out as well. Minus the kick start of course.
« Last Edit: April 01, 2021, 11:31:11 AM by caluser2000 »
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Offline Ryan66

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Re: CB550 Reseal and 650 Cam Swap
« Reply #18 on: April 01, 2021, 11:27:17 AM »
Quote from: JLeather on April 01, 2021, 09:58:59 AM
I believe that site is incorrect regarding the 650 tach ratio.  This is excerpted from the forum FAQ:

CB750 Speedo  2240:60  Tach 4:1
CB650 Speedo  2240:60  Tach 4:1
CB550 Speedo  2240:60  Tach 20:3
CB500 Speedo  2240:60  Tach 20:3
CB400 Speedo  2240:60  Tach 20:3
CB350 Speedo  2240:60  Tach 20:3

This is bolstered by the experience of others who've done the 650 cam swap and had to change tachs.

EDIT - I've not yet done either of the above yet...  I'd be quite happy if my 550 tach works as it's in better shape (and matching) as compared to the 750 tachs I've got.
So i may be correct in saying some or all years 750 tachs are the same as the sohc 650 tach.
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Offline caluser2000

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Re: CB550 Reseal and 650 Cam Swap
« Reply #19 on: April 03, 2021, 08:48:22 PM »
Engine tacho drive housing is the same on SOHC 500/550/650 machines.

https://www.nospartsnow.com/nos-honda-cb500-cb550-cb550f-cb650-cb650sc-tachometer-gear-holder-cap-12451-323-000/

The tacho gear from the cam sharft to the tacho cable is a different part number on the CB650 though.
« Last Edit: April 03, 2021, 09:11:32 PM by caluser2000 »
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Offline Kevnz

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Re: CB550 Reseal and 650 Cam Swap
« Reply #20 on: April 03, 2021, 10:23:41 PM »
Please excuse my ignorance, but is there some advantage to be gained from using a 650 cam?
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Offline scunny

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Re: CB550 Reseal and 650 Cam Swap
« Reply #21 on: April 03, 2021, 11:37:30 PM »
Good question Kev, I think( dangerous as it sounds) the 650 cam feels different, had several 500's before, but the 650 I now have  seems to have a fatter mid range, I don't know if that is just the cc increase or the combination of both. Apparently the 650 cam has more valve overlap. I have just sold one to a guy building a 500 race bike. Included the tacho drive, don't know if he needed it or not.
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Offline Ryan66

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Re: CB550 Reseal and 650 Cam Swap
« Reply #22 on: April 04, 2021, 06:25:24 PM »
These are the lift specs for 550 and 650. The 650 also has 8 degrees more duration also.
CB650    IN .280
            EX .293

CB550    IN .252
            EX .272
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Offline JLeather

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Re: CB550 Reseal and 650 Cam Swap
« Reply #23 on: April 29, 2021, 05:38:29 AM »
Haven't made as much progress as I'd hoped, but I'm as far as having the head back on.  Found a couple gouges on the head indicating that someone has been in the motor before me and used it as an excuse to plane it about .020"  ;D  Also replaced the cam chain tensioner slipper and fixed the tension mechanism (one of the little gear teeth was bent and had jammed the screw).  Next up is the cam...

« Last Edit: April 29, 2021, 06:08:08 AM by JLeather »
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Offline JLeather

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Re: CB550 Reseal and 650 Cam Swap
« Reply #24 on: May 03, 2021, 08:45:56 PM »
Well, 2 steps forward and 5 steps back I guess.  As I said before I found evidence that someone who was less than careful has been in this engine before.  A little more of their handwork struck tonight.  I was going through the top end and putting the valve cover together and back on when this happened.  One of the studs/wedges that holes the rocker shafts in place pulled out.  Turns out there is an old and shoddy weld repair, presumably because someone before me overtightened and broke the casting.  I don't think I'm comfortable with a repair here, even if it was done better, so I'm in search of a '77/'78 550 valve cover.
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