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Author Topic: CB550 white smoke after top end rebuild  (Read 703 times)

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Offline JB Stellies

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CB550 white smoke after top end rebuild
« on: December 05, 2018, 08:43:16 am »
I did a top end rebuild after incorrect installation of tappet cover resulting in bent exhaust valves (noob mistake- followed workshop manual without watching youtube tutorials). Now the bike is smoking like a two stroke. I outsourced the valve replacement as I did not have the tool to compress the valves and the mechanic ensures me that the valve guides were not cracked and that valve stem seals are OK. I used aftermarket generic o-rings on the oil channels either side of the head. If these were not thick enough, could it result in white smoke/what would the symptom be? I have ridden 15km, the bike is running well (other than the white smoke) and there are no visible external oil leaks. The bike was not smoking before the top end rebuild and I did not touch the bottom end so I am confident that the rings are OK.

Offline TwoTired

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Re: CB550 white smoke after top end rebuild
« Reply #1 on: December 05, 2018, 09:08:16 am »
White smoke is water vapor, generally.
Blue smoke is oil smoke.

Are you certain that water condensate in the exhaust is not the source of the "smoke"?  Have the exhaust been thoroughly heated to flash off the condensate?

Are all head pipes getting evenly hot?

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Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #2 on: December 05, 2018, 10:48:19 pm »
I am pretty sure it is oil and we are talking about a large amount of smoke. It is worse at first start up but smokes heavily and consistently thereafter. I will check if all exhausts are heating up evenly when I next ride.

Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #3 on: December 05, 2018, 10:52:28 pm »
PS - and yes, after 15km I think the bike was pretty hot and any condensate and residual oil from the rebuild should have burnt off. Thks

Offline TwoTired

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Re: CB550 white smoke after top end rebuild
« Reply #4 on: December 06, 2018, 08:22:40 am »
Tell us how you routed the top engine vent hose.
Can the crankcase still "breathe"?

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Lloyd... (SOHC4 #11 Original Mail List)
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Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #5 on: December 07, 2018, 07:37:48 am »
I have not fitted a vent hose.

Offline Deltarider

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Re: CB550 white smoke after top end rebuild
« Reply #6 on: December 07, 2018, 07:54:22 am »
Well, there's the source of your smoke, probably
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Offline TwoTired

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Re: CB550 white smoke after top end rebuild
« Reply #7 on: December 07, 2018, 09:22:43 am »
I have not fitted a vent hose.
Is the hose nipple open or plugged?
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Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #8 on: December 12, 2018, 07:47:00 am »
Vent nipple is open, photo attached tv. Have been running it without a hose since I got tbe bike with no problem.

Offline Don R

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Re: CB550 white smoke after top end rebuild
« Reply #9 on: December 12, 2018, 08:09:33 am »
 My buddy ran across a breather tube filled with silicone, it caused a similar problem. Just my friends experience.
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Offline TwoTired

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Re: CB550 white smoke after top end rebuild
« Reply #10 on: December 12, 2018, 08:18:24 am »
Vent nipple is open, photo attached tv. Have been running it without a hose since I got tbe bike with no problem.

...Except for the bugs that crawl in and nest, or abrasive dust invasion.  Rain or wash water ingress?
And, if you do get excessive piston ring blow by, the engine oil sprays out of there covering the entire rear of the bike.  If it weren't a required item, why do you think Honda went to the expense of installing one on every bike they sold?  Give them a little credit, please.

Anyway, it's good that you didn't plug it off.  We can check crankcase pressure build up off the possible cause list.  I was looking for cheap and easy fixes.  Now it warrants a more serious investigation.

If you have excessive oil smoke, it is getting past the valve guide seals or the piston rings. (or leaking onto the exhaust system.)  Time for a leak down cylinder check, or at least a compression check, to ensure mechanical health of the cylinders.

Do the spark plug deposits show anything interesting?  Are they the same for each cylinder position?  Did you verify each head pipe runs at about equal temperature?  We need to know if all four pots are burning, or if one is just pumping fuel/air without igniting. If the latter, white fuel vapor out the exhaust is a possibility. 

Have you checked for spark at each position?

Cheers,

Lloyd... (SOHC4 #11 Original Mail List)
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Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #11 on: December 12, 2018, 08:52:42 am »
Thanks gents. New rings about 1000km ago and did not touch the block and it was running fine before I took the head off so I am confident rings fine. My guess is that mechanic did not check for cracked valve guides and that one or more exhaust valve guides cracked when the valves bent. When I asked the mechanic if he checked he said he would need to check with the guy who did the work so my guess is he did not give clear instructions to his junior. Attached photo of smoking bike.

Offline PeWe

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Re: CB550 white smoke after top end rebuild
« Reply #12 on: December 12, 2018, 08:58:01 am »
Vent nipple is open, photo attached tv. Have been running it without a hose since I got tbe bike with no problem.
You have not felt any stinky warm oil smell right up in your face while waiting for green light with warm engine?

My CB750 K6 had a long hose from valve cover breather going backwards on right side to the rear passenger foot peg. Old hose hardened and cracked. Now a shorter one ending just behind main foot peg.
Std car 1/2" oil/heater hose work fine. A little bit thick... Honda used thinner walled hose without braiding.
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Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #13 on: December 12, 2018, 09:02:02 am »
Thanks, I will fit a hose when I put the engine back together again after sorting out the cause of the smoking.

Offline bryanj

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Re: CB550 white smoke after top end rebuild
« Reply #14 on: December 12, 2018, 01:36:32 pm »
If the valves were bent i would be 90% certain the guides were broken somehow. If you fit new they need to be ACCURATELY reamed to size and the seats re ground to suit.

The size reamer is not a "standard" size so unless it is a shop that does a lot of Hondas an adjustable one tends to get used and they are simply not good enough.
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Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #15 on: December 13, 2018, 06:21:34 am »
Thanks Bryanj. Will have a careful look at valve guides when it is in pieces again. I have a full spare engine in parts and may be better to use that head but cam chain tensioner broke on that engine and cam chain slipped so not sure what damage that may have caused to the head if any. Cannot see any visible damage to the head.

Offline bryanj

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Re: CB550 white smoke after top end rebuild
« Reply #16 on: December 13, 2018, 10:03:17 am »
Easy check to see if valves are reasonable is to stand head on exhaust outlets then fill inlets with gas or keroseen and see if any apears in combusion area then put head on inlets and fill exhaust. Easier to see which, if any, valves are leaking than the book way of filling combustion chamber.
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Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #17 on: December 13, 2018, 10:25:30 am »
Thanks Bryan, great tip.

Offline calj737

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Re: CB550 white smoke after top end rebuild
« Reply #18 on: December 13, 2018, 11:22:30 am »
Easy check to see if valves are reasonable is to stand head on exhaust outlets then fill inlets with gas or keroseen and see if any apears in combusion area then put head on inlets and fill exhaust. Easier to see which, if any, valves are leaking than the book way of filling combustion chamber.
This will only tell you whether or not the valve face is seating do sealing fully, not whether the guide is worn. You could easily have carbon build up on the valve face, preventing full seating, but good guides. Conversely, worn guides that under operating conditions allow the valve to move off their axis, but freshly lapped faces that seat.

Unless I’m missing something?
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Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #19 on: December 13, 2018, 12:12:44 pm »
Makes sense unless you can look for gasoline leaking through on either side with that test (valve seat and stem ends)?

Offline calj737

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Re: CB550 white smoke after top end rebuild
« Reply #20 on: December 13, 2018, 12:20:19 pm »
Makes sense unless you can look for gasoline leaking through on either side with that test (valve seat and stem ends)?
Maybe I made my point in a confusing fashion, or I’m confused. I see where that technique addresses the valve seat. But I don’t see where it addresses valve guide wear.
Thanks Bryanj. Will have a careful look at valve guides when it is in pieces again.
Wasn’t that your point with this post?
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Offline bryanj

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Re: CB550 white smoke after top end rebuild
« Reply #21 on: December 13, 2018, 01:08:06 pm »
It doesnt asses guide wear BUT it gives you a good idea of the valve/seat condition BEFORE you spend any money especially on a used head of unknown condition.

We already know that the fitted one has problems and when you get to valve/guide/seat replacement or repair it is frquently far more cost effective to find a good used head.
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Offline calj737

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Re: CB550 white smoke after top end rebuild
« Reply #22 on: December 13, 2018, 03:00:46 pm »
It doesnt asses guide wear BUT it gives you a good idea of the valve/seat condition BEFORE you spend any money especially on a used head of unknown condition.

We already know that the fitted one has problems and when you get to valve/guide/seat replacement or repair it is frquently far more cost effective to find a good used head.
That’s what I thought. Thanks for the clarification.
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Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #23 on: December 13, 2018, 10:02:09 pm »
Thanks gents! Understood.

Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #24 on: December 13, 2018, 11:06:36 pm »
I need to order a gasket set from the US so will only tackle this project in January. Will keep you all posted then. Thanks to everyone for input and advice. My experience working on multi-cylinder four strokes is very limited.

Offline bryanj

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Re: CB550 white smoke after top end rebuild
« Reply #25 on: December 14, 2018, 12:07:23 am »
No more difficult than any twin i worked on and way easier than Norton or BSA! Just remember to be super clean on rebuild.
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Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #26 on: December 14, 2018, 01:34:40 am »
..........but quite different to a single cylinder two stroke :)

Offline JB Stellies

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Re: CB550 white smoke after top end rebuild
« Reply #27 on: January 08, 2019, 09:04:50 am »
The engine is apart again and the cause of the white smoke was cracked valve stem guides. Luckily I have a spare engine and the head looks OK, crossing fingers. Thanks to all who offered advice.

Offline alacrity

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Re: CB550 white smoke after top end rebuild
« Reply #28 on: January 08, 2019, 09:16:28 am »
The engine is apart again and the cause of the white smoke was cracked valve stem guides. Luckily I have a spare engine and the head looks OK, crossing fingers. Thanks to all who offered advice.

Hey there.  Pro tip:  before you put this all back together, knock out the valve guides and put New OEM honda seals in there (little Viton o-rings) and also only use honda oem valve STEM seals (the structured ones with the little springs).  I have had to re-do top ends way too soon because of crappy aftermarket seals that harden and leak.  The result is always white smoke, most noticeable on start up.
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Offline bryanj

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Re: CB550 white smoke after top end rebuild
« Reply #29 on: January 08, 2019, 09:34:50 am »
Sorry dissagree there and would NEVER remove guides unless new was being fitted as they never go back exactly the same so a valve job is then needed. Never ever had a "leak" from the guide external O ring but many broken stem seals.

READ THE MANUAL about refitting valve cover then go back and READ IT AGAIN until you fully understand what can happen if you do not hold the cam followers up.

Not doing that is probably why your original guides were cracked!
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Offline calj737

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Re: CB550 white smoke after top end rebuild
« Reply #30 on: January 08, 2019, 09:42:33 am »
The engine is apart again and the cause of the white smoke was cracked valve stem guides. Luckily I have a spare engine and the head looks OK, crossing fingers. Thanks to all who offered advice.

Hey there.  Pro tip:  before you put this all back together, knock out the valve guides and put New OEM honda seals in there (little Viton o-rings) and also only use honda oem valve STEM seals (the structured ones with the little springs).  I have had to re-do top ends way too soon because of crappy aftermarket seals that harden and leak.  The result is always white smoke, most noticeable on start up.
I think you’re a bit confused. The guides do not need to be removed to replace the seals. If a guide is removed, as bryanj says, the valve seats must be re-cut. This should not be considered a routine maintenance procedure, only a repair process.
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Offline alacrity

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Re: CB550 white smoke after top end rebuild
« Reply #31 on: January 08, 2019, 10:38:20 am »
Hi Cal!  I am often confused and even more often confusing. But in this case?  Once it is determined the smoke is coming from oil leaking into the combustion chamber, there are really only three ways for that to happen: Blow past the rings and/or leaky valve STEM seals and/or leaky valve GUIDE seals.  If there was no need for valve guide seals, would Honda have installed them? If they never wear out/need replacing, would they stock and sell new ones?  This is why on every top end I do, I pull the guides and mic them (replace as needed - stock part 12023-465-405 or dynoman sells good aftermarket brass ones, for example) and ALWAYS replace all 8 of the stem and all 8 of the guide seals. You might get lucky and have the valve guides not leak. But why not freshen those components as well while the thing is apart? Why count on really old o-rings and possibly loose/bad fitting/messed up guides (maybe someone replaced a bent valve 20 years ago and didn't replace the now marred guide? etc). Of course all this is about oil control issues -- not combustion/performance issues.

The engine is apart again and the cause of the white smoke was cracked valve stem guides. Luckily I have a spare engine and the head looks OK, crossing fingers. Thanks to all who offered advice.

Hey there.  Pro tip:  before you put this all back together, knock out the valve guides and put New OEM honda seals in there (little Viton o-rings) and also only use honda oem valve STEM seals (the structured ones with the little springs).  I have had to re-do top ends way too soon because of crappy aftermarket seals that harden and leak.  The result is always white smoke, most noticeable on start up.
I think you’re a bit confused. The guides do not need to be removed to replace the seals. If a guide is removed, as bryanj says, the valve seats must be re-cut. This should not be considered a routine maintenance procedure, only a repair process.
I just restored a lovely 77 cb750f, and am searching for another low mileage cb500/cb550 to do next.  This is a place to share, learn and enjoy.  I am grateful to and for 99+% of this site's membership.

Offline calj737

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Re: CB550 white smoke after top end rebuild
« Reply #32 on: January 08, 2019, 10:47:59 am »
Your post said: “knock out the guides and replace the seals.... as it’s something I routinely do”. You make no mention of recurring seats, and as I said, replacing seals does not necessitate guide removal.

If a guide is worn, replace it (as I said). If it’s not worn, replacing it is superfluous and costly. The OP had a cracked guide if I recall now, certainly cause to replace that one (and any other in need). But replacement for the sake of replacement is foolish and zero benefit.
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Offline bryanj

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Re: CB550 white smoke after top end rebuild
« Reply #33 on: January 08, 2019, 05:02:19 pm »
In 40+years this is the only time i have ever heard advocated removing guides to replace an O ring.
Every time you take a guide out you loose metal from the head and have to recut the seat so loose metal from there as well as recessing the valve head. Replace O ring when guide needs replacing yes but again i have only ever seen guides worn out on 750F2/3 and damaged by incorrect assembly on 500/550 apart from totally destroyed engines after missuse.
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Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

 

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