Topic: cb550 top end rebuild, advice needed please ***pics added***

[Bru-tom]

Hey guys,

so, i stripped the head off to fix a leak on my newly purchased cb550 and thought i would make sure everything is still fine inside at the same time. The motor never smoked when i rode it, sounded decent enough. i did a compression test with my super long tester which inevitably would give me a lower reading along with a ice cold motor, with throttle wide open, read 112, 110, 108 , 110psi. not to bad considering.

Head came off, gasket took about 2 hours to scrape off, what a pain! the cam tensioner housing thing is slight damaged on the bottom side, looks like it had been rubbing, assuming the PO installed it incorrectly. i dont think it needs replacing, however the blade has some grooves from the chain. the cam chain guide on the other side also showed some grooves. think i will replace them both.

now, since i removed the head and after tugging quite hard to pry it loose, the jugs lifted. so i think i want to replace that gasket and the o-rings around the barrels while its all open.

**** my question is, should i replace the rings with standard size while its open an hone the sleeves? i mean, i didnt see any excessive wear of marks on the bores, and my compression test wasn't so bad to say that i should use oversize parts?



***** second question, what can i use to clean a build up of carbon on the valves and combustion chambers and tops of pistons?

i did do a seal test on the valves, flipped the head ovver and poured petrol in the chambers and the valves still seal good and proper.

any other advice would be awesome!

thanks for looking guys

[MoMo]

You could either replace with standard rings, or check the end gap of the ones you have and if within specs use a glass bead hone and reinstall what you have,, I use a really soft wire wheel on my bench grinder to remove carbon.  Relap valves and you should be good to go, make sure you replace any rubber pucks and o-rings...Larry

[Bru-tom]

You could either replace with standard rings, or check the end gap of the ones you have and if within specs use a glass bead hone and reinstall what you have,, I use a really soft wire wheel on my bench grinder to remove carbon.  Relap valves and you should be good to go, make sure you replace any rubber pucks and o-rings...Larry

thanks for the advice MoMo.

when you refer to end gaps, do you mean  the ring gap when inserted in the sleeve and measuring it with a feeler gauge?

so i should remove the valves from the head with springs ect, making sure all the parts are marked as to where they came from without mixing any up, and use valve grinding paste and spinning them on their respective seats?

the carbon build up is quite bad on the combustion chambers, should i remove valves then clean? wont the wire brush damage the seats?

[DustyRags]

The valves are very hard, so a soft wire brush shouldn't damage them. The carbon is so much softer.

You can probably use the same rings, check to see if they're in spec, and if yes, you're good to go! When I did mine, I didn't really hole the cylinders so much as just scuff them a bit with some 220 sandpaper going around the outside (crosswise to the stroke direction). Is it a proper hone? No, but the guy who suggested this was a Honda race mechanic who used to work on these back in the 70's, so I trust him. Worked fine, for jugs that were pretty much fine.

[Bru-tom]

The valves are very hard, so a soft wire brush shouldn't damage them. The carbon is so much softer.

You can probably use the same rings, check to see if they're in spec, and if yes, you're good to go! When I did mine, I didn't really hole the cylinders so much as just scuff them a bit with some 220 sandpaper going around the outside (crosswise to the stroke direction). Is it a proper hone? No, but the guy who suggested this was a Honda race mechanic who used to work on these back in the 70's, so I trust him. Worked fine, for jugs that were pretty much fine.

thanks a ton Mr DR.

how do i check the rings? i like the way you honed yours, you basically spiraled the paper up and down from different points giving it a cross hatched effect?

is it okay to have your piston move slightly when pressed with thumbs from side to side along the gudgeon pin?

[MoMo]

Check the end gap the way you mentioned-insert into cylinder(I use the piston to make sure ring is level) and measure with feeler gauge-not sure of limit but it is in the manual.  Don't mix up rings and valves as DR said. I have a glass bead hone but his technique could work...Larry

[TwoTired]

The rings, pistons, and cylinders worked well and sealed before and are already married to each other.  Do not swap any internal parts among cylinders.  Don't change a thing except the cylinder base gasket. (Unless you damage a ring/piston putting the cylinder back over the piston.
Then it is new rings and a hone so they will seat in properly/quickly.)

You were only fixing oil leaks, right?  I see no evidence you need a top end job at all.

[DustyRags]

Listen to TwoTired. That man's a living repository of all things 550, and he has a point- so far, NOTHING points to a top-end rebuild. Replace your gaskets, and let it go.

[Bru-tom]

The rings, pistons, and cylinders worked well and sealed before and are already married to each other.  Do not swap any internal parts among cylinders.  Don't change a thing except the cylinder base gasket. (Unless you damage a ring/piston putting the cylinder back over the piston.
Then it is new rings and a hone so they will seat in properly/quickly.)

You were only fixing oil leaks, right?  I see no evidence you need a top end job at all.

thank you all for chiming in so i shouldnt clean the bores at all? just the piston tops and thats it? sot the tensioners out and replace the chain, clean the combustion chambers and valves. Should i take valves out and replace stem seals?

i just thought that while its open, i may as well do some maintenance so i wont have to in a long while to come...

[dave500]

id be doing the valve seals and re lap the valves.

[Bru-tom]

id be doing the valve seals and re lap the valves.

thanks mate, i think il feel better knowing i mainatined something

[cabrala]

I think you don't want to delve too far into, by your account, a good running bike. It's very easy to get caught up in the, "while it's open I might as well...", but I'd defer to TT here and just replace some gaskets, reassemble and be ready to ride.

[Bru-tom]

i am on a tight budget afterall.

i think i will just clean the carbon build up on chambers and piston tops.

what about the tensioners? there are some decent grooves in the blade and guide?

[TwoTired]

what about the tensioners? there are some decent grooves in the blade and guide?

The guides shoes are sacrificial, and will always show wear from a running engine.  Like brake shoes/pads you don't replace them at the first sign of wear, but rather when it is apparent they are close to end of wear life.
We can't tell what you perceive to be "decent grooves" from your description alone.  Either puts some numbers/measurements in your description, or post pictures showing what concerns you.

Have you even told us the service life of the motor? (I haven't re-read the entire thread) 10K miles, 30 K miles, 60K miles?
If high miles, then you'll want to get deeper into the engine to check the primary chain wear.

You also might want to state your goals for this engine.  Like new, pristine, is going to cost money, time, and effort.  A serviceable, reliable engine for it's normal service life on the street doesn't need like-new clearances and wear limits in each and every part of the engine.

Now, if you want race day durability and reliability, from the engine, you're going to need a bigger budget.

Cheers,

[Bru-tom]

The guides shoes are sacrificial, and will always show wear from a running engine.  Like brake shoes/pads you don't replace them at the first sign of wear, but rather when it is apparent they are close to end of wear life.
We can't tell what you perceive to be "decent grooves" from your description alone.  Either puts some numbers/measurements in your description, or post pictures showing what concerns you.

Have you even told us the service life of the motor? (I haven't re-read the entire thread) 10K miles, 30 K miles, 60K miles?
If high miles, then you'll want to get deeper into the engine to check the primary chain wear.

You also might want to state your goals for this engine.  Like new, pristine, is going to cost money, time, and effort.  A serviceable, reliable engine for it's normal service life on the street doesn't need like-new clearances and wear limits in each and every part of the engine.

Now, if you want race day durability and reliability, from the engine, you're going to need a bigger budget.

Cheers,

thanks mate, you know who you remind me of, my resident VW guru on our local forum, is very knowledgeable about everything VW, much like you with Honda motorcycles, and his name nic is "panic-mechanic" hahaha. must be a guru thing

i have taken some pics of the guide and blade shoes. there is also that metal rubbing wear at the bottom, also pictured, but i dont think it will effect its operation? what could have caused that?









here are some pics of the pistons and combustion chambers. the comb chambers were filled with fuel at the time. ANd no, the first one wasnt leaking as it appears, i did that one first and when i poured fuel into the others, it ran into the first one.

how would i clean the gasket mating surfaces?





how would i clean the carbon off both the piston tops and valves, soft wire brush as stated previously?

the odo says she has done 32000km....i dont know how true that is?

i would like to get her running well, i mean, i dont mind spending money, but cant afford a fortune yet, im an apprentice, so i might want to wait until im qualified i mean, a gasket set is like 100 dollars, plus importing it to South Africa. there are some valve setting lock nuts that i need to replace as they were basically stripped by PO.

here are some more pics:

rockers look great still:





thanks for your help mate

[TwoTired]

I'd reuse those guide shoes without a second thought.
The metal wear looks like a bit of wear from movement in its captive placement mounts.  I bit of polishing wouldn't concern me.  But, I'd like to know why it was moving around so much.  Still, if the mechanism presents the shoe to chain in proper manner, I don't see why it can't continue to perform its proper function.  Is the adjuster portion still functioning correctly?

[dave500]

dont forget to tell bru tom about getting the tensioner back into its locating slot correctly tt.

[TwoTired]

dont forget to tell bru tom about getting the tensioner back into its locating slot correctly tt.

Ok

+1

But really, I'd be more apt to warn about putting the cam cover back on without bending the valves.  Check the shop manual for a drawing.

Cheers,

[DustyRags]

Oh good grief, that stupid tensioner thing! Yeah, make sure it's seated correctly- if you can see it from the bottom with the oil pan off, it ain't in the right place. And you can't check that with the oil pan on, so just bite the bullet and drop the bastard. Attach it to the barrels with the lock screw, then drop the whole shebang in place.

On that note- make sure the lock nut is locking against the barrels and not the end of the threads. That happened to mine, and the PO didn't figure it out and stripped it. I ended up doing a full top-end rebuild.

And listen to them on the tappets. Back the set screws all the way out, and then throw some rubber bands on them to keep them up, up, up when you cinch the head back down.

Really, why am I saying all this? Dave and TwoTired are the gurus, I'm just puking back up what they told me when I built mine 'cause it was so useful

[Bru-tom]

thanks guys! i think the PO never seated the tensioner correctly, hence the rubbing. nut i really dont mind whooping the sump off and making sure. i would like to see whats lurking in there anyway, and replace the gasket...

i know about the valves, i watched a vid that soco posted on youtube where he used the elastic bands.i also loosened off the tappet adjusters and thats when i saw several of the nuts were stripped

so how should i still go the soft wire brush route to clean my lil piston tops and champers up?

[DustyRags]

The head's aluminum, so you won't want to use a motorized brush on it. I think I used carb cleaner on mine, in generous doses.

[Bru-tom]

yeah, alli is soft stuff.

after stripping my carbs to the bone to soda blast, i noticed that the idle screws were all different. one was 5 turns out and others were 3, 4 and 2 turns out from bottom. that could be why there is so much carbon build up maybe?

[TwoTired]

You have told us what model bike you have?
Unless you have a PD carb model, you can expect the engine to run pretty rich at idle and will be moreso with choke operation.  These conditions lend themselves to carbon build up.  The removal of carbon occurs when the engine is made to produce full power, which gets the carbon hot enough to burn off or dislodge and exit the exhaust.  Again this depends on how the fuel mixtures were set.  But, the way it was driven daily also matters.  These engines were not meant to be babied and remain in the low RPM regime.  Imo, you aren't doing them any favors by keeping them below 5000 RPM, or reducing the RPM on the freeway with gearing changes.

Anyway, while the carbs determine fuel mixtures, they are dumb and non-adaptive. The factory settings and adjustments work rather well as long as the engine is left in stock form as well as the induction and exhaust characteristics.

If you have PD carbs, 5 turns outs is further enrichment if the idle mix and more chance of carbon during idle conditions.
If you have earlier style carbs, 5 turns out is a leaner setting than stock.

Are the cylinder carbon deposit patterns different among cylinders?  Do the deposit pattern differences coincide with carb screw settings?
I would certainly clean carbon build up while it is disassembled.  (I'm not all all sure why you needed to take it apart in first place.)  However, if the surface is just dark and less than a 1/64 or 1/32 of an inch, I'd probably let it go for a street bike.

However, all that carbon deposits do is raise the compression ratio, which actually helps the engine to make more power.  Clearly, when this gets extreme, pinging, detonation, and/or the need for higher octane fuel occurs.  A compression test that shows too high a compression value (using a proper tester), means a de-coking, de-carbon effort is required.

The cylinder simply does not run clean.  They can't, especially with an air cooled engine, as the cooling system is excessive 80- 90% of the time.  And this leads to inefficient mixture burn in the cylinders. 

Do scrape off any deposits that are significant, particularly burrs, or edges, and try to keep get all the pistons/chambers equal in volume.  There are decarbonizing techniques that simply mist water into the carb intake while the engine is producing power (high heat).  This can do in a few seconds what hours of scraping can do.

Just how thick is the carbon you are seeing, that warrants a "so much" label?

Cheers,

[74750k4]

"the cooling system is excessive 80- 90% of the time"

Very good point. Otherwise it would be overheating 10-20% of the time. Which proves the over 5000 RPM theory of operation.

[Bru-tom]

sorry, was  registered 77, but the engine number and frame numbers differ..

Engine #: CB550E 1122878
Frame #: 1012521

thanks for the lesson TT, always a pleasure reading your posts! The motor had an oil leak on the right cylinder, the oil would run to the edge and fly off with the wind and burn the sh!t into my leg hence the opening up of the motor.

here is what i am going to do...clean the carbon build up best i can... replace gaskets and close her up. DONE.

i did however need to service my carbs properly, o-rings were all torn up and perished. i will take them to a industrial suppler and have them match to my requirements and reassemble after cleaning thoroughly.

i did get a flat spot at about 4krpm, after that she pulled like a beast. could have been due to the idle settings and dirty carbs. that was the first and last time i rode her and the strip down began. she was in a poor state.