Topic: CB550 Reseal and 650 Cam Swap

[JLeather]

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?

[Ryan66]

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.

[caluser2000]

CB650 and CB750 tachos  are different ratios.

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

[Ryan66]

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.

[Scott S]

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.

[Ryan66]

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.

[caluser2000]

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...

[Alan F.]

Is this cam swap applicable to 500 models or just 550s?

[Scott S]

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.

[bryanj]

500 and 550 heads are identical

[caluser2000]

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.

[Alan F.]

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.

[caluser2000]

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!

[JLeather]

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...

[JLeather]

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.

[caluser2000]

750 and 650 tachos are different ratios:

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

650/550s/500s are 7:1

750s are 4:1

[JLeather]

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.

[caluser2000]

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.

[Ryan66]

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.

[caluser2000]

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.

[Kevnz]

Please excuse my ignorance, but is there some advantage to be gained from using a 650 cam?

[scunny]

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.

[Ryan66]

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

[JLeather]

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"    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...

[JLeather]

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.

[bryanj]

If you can live without the pined shafts, which worked for a lot of years, any 500/550 will fit

[JLeather]

If you can live without the pined shafts, which worked for a lot of years, any 500/550 will fit

Thanks for the info. The earlier ones seem easier to find. At the moment I just wanna get the bike back on the road. I assume if I got an earlier cover I'd need to get a complete one with shafts?

Sent from my moto g(6) using Tapatalk

[bryanj]

Idealy yes

[JLeather]

I think I've got it worked out.  I put out a call on FB and a friend of mine had a rough 550 engine (side covers off, internals unknown) so I bought the whole thing for $75.  It was a '76 by the numbers but when I opened it up it had the later valve cover.  Now I've got a good cover and a head to try porting later, plus any other spares that turn out to be good.  Threw a quick coat of Duplicolor "aluminum" on it last night, oughta be able to get it on and set the valves tonight.

[JLeather]

New cover painted and installed (not as pretty as the polished one but I'm not paying for that right now).  Managed to run the bike for a few minutes last night for a leak check, but it needs the carbs synched again after all this work and probably some tuning for the 650 cam and increased compression.

One annoying thing, when I fired it up for the first time it was only running on 1/4.  This was a solid running bike when I did this topend work and nothing should have changed in the ignition.  Checked for 12v at the coils, checked for 12v at the points, didn't find anything wrong but the timing light confirmed I had absolutely no spark on 2/3 after running it for a few minutes.  Left the light hooked up and decided to fire the points manually with a screwdriver while I fiddled with things.  First time I opened the 2/3 points with the screwdriver they fired (and lit off a bunch of unburned fuel in the pipes lol) and after that the bike ran fine.  I guess they were hung up somehow, but I can't figure out how.  I'd like to make sure it doesn't happen out on the road?

[bryanj]

Crap on the surfaces-------this is not an instruction

[JLeather]

Crap on the surfaces-------this is not an instruction

Hahahaha.  That's what I figured, but I'm surprised that a few minutes of running didn't dislodge it but one time firing the points with a screwdriver did.  Weird.  We'll see how she does after a tune-up and test ride this weekend.

[JLeather]

All back together.  New carb synch, which was way different than the one I just did a couple months ago.  The carb tune is nearly unchanged.  It's about 1/2 a turn leaner on the idle screws, and while I had the carbs off I bumped the mains up to 92's since it was a little lean stock.  Otherwise it feels good.  Knock on wood no leaks so far.

[wolf550]

very nice work.