Topic: Advice on cylinder streaks (CB550)

[wmajinw]

Found this inside my cylinders.

I couldn't feel the streaks under my fingernail, with the exception of one streak which was at the botton of the cylinder and felt more like an indentation and not a streak as it did not snag my fingernail.

Any suggestions on what to do or should I just leave it as it is?

Prior to disassembly the bike ran good and did not throw any smoke.

Didn't have the tools so didn't do a compression test yet.

[denward17]

Since the scuffing goes all the way to the top, it appears to be ring related.

Do you have the cylinders off yet?
Were any of the rings damaged?

Could you measure ring end gap now?

[wmajinw]

Haven't taken off the cylinders yet.

But thanks for the idea to check the piston rings for damage.

[wmajinw]

Checked the piston ring prices and it seems its that just the piston rings are more expensive than a whole set of piston reolacement oarts (pistons included).

Any advice on what to avoid?

[bryanj]

Either broken ring or run without airfilter but needs adressing, if you buy same size pistons and hone the marks out it will burn oil if you go oversize and rebore make sure its done by a motorcycle savy firm as clearances need to be tight

[denward17]

"Any suggestions on what to do or should I just leave it as it is?"


As Bryanj stated, the best fix is to take it apart and have it rebored either +.25mm or +.5mm.  There are aftermarket pistons sets available.

I just did this myself, check my project page in my signature.

How many miles on the bike and what is your plan for it, just a rider or race....only you can decide how far to go.

[wmajinw]

"Any suggestions on what to do or should I just leave it as it is?"


As Bryanj stated, the best fix is to take it apart and have it rebored either +.25mm or +.5mm.  There are aftermarket pistons sets available.

I just did this myself, check my project page in my signature.

How many miles on the bike and what is your plan for it, just a rider or race....only you can decide how far to go.

I plan to ride it occasionally, since I have another daily driver.

It's my first serious project bike and I already spent more on parts than on the bike itself.

Ideally I'm planning to measure the bore of the cylinder and if it's in spec I'd just hone it and replace the piston rings. Hence me asking what manufacturers to avoid for ring sets or complete piston kits.

[bryanj]

Like i said if you hone it the piston to bore clearance gets too big

[Stev-o]

"Any suggestions on what to do or should I just leave it as it is?"


As Bryanj stated, the best fix is to take it apart and have it rebored either +.25mm or +.5mm.  There are aftermarket pistons sets available.

I just did this myself, check my project page in my signature.

How many miles on the bike and what is your plan for it, just a rider or race....only you can decide how far to go.

It's my first serious project bike and I already spent more on parts than on the bike itself.

Sometimes the cheapest bike become the most expensive!  [been there]

Need to do more investigating before making the proper decision.

[bryanj]

You want to make it pop you can overbore to plus 3mm making it over 600cc, kits from cruzinimage in japan

[MauiK3]

I'll +1
Have a motorcycle savvy person hone it.
Better yet, have a really good one do it AND fit the pistons.
Hondaman comes to mind and there are others.
Shortchange this and you will be sad.

[calj737]

Ideally I'm planning to measure the bore of the cylinder and if it's in spec I'd just hone it and replace the piston rings.

It is possible to freshen the cylinder with a hone without increasing the bore size, but its a VERY close tolerance. Honestly, if you take it far enough apart to hone it, the cost of pistons and boring become negligible over the life of the bike when you amortize it against your time/money.

Any cheap/inexpensive project bike becomes far more costly once parts get replaced. Nature of the beast. Buy cheap, spend big. Buy big, spend less. Any decent automotive machine shop armed with the piston maker's tolerances can and will do a perfectly good job. Just have to find a competent shop in your area, or you can ship the work out and get guaranteed results.

Your profile does not list your actual location, so recommendations for you locally are difficult to offer.

[wmajinw]

UPDATE:

Got in touch with a local oldtimer who's been working on old bikes for a long time.

We checked the piston to cylinder clearances and all 4 were 0.08. Funny thing is that he said that you can tell if the clearances are ok by removing the piston rings and letting it from in the cylinder - how fast the cylinder drops usually tells if the clearances are ok. He did that with one of the cylinders and said that the clearance should be about 0.08 (this was before we did the measuring). I guess when you've been working all your life on bikes you catch on some tricks, but this was straight out like fortune-telling for me.

Anyway, he said that its strange that there are these streaks, because the engine looks like newly refurbished and the honing done on the cylinders is very good.

One thing he said that needs to be fixed is the pistons themselves. There's some smooth shiny spots on the piston skirts and he said that might be a problem, because oil won't stick to it, which could result in a seized engine. His advice was to get some 240-320 grit sand paper and just make a couple horizontal passes on the shiny spots to make some grooves for the oil to stick.

[rotortiller]

If you cannot feel the  vertical marks with your finger nail I would not be concerned. Since the cylinders off I'd go a pass or two with the hone, very sparingly. Since the tech measured the piston skirt and the cylinder to arrive at the .003"clearance you might be able to do as he suggests to the skirts but very lightly with say scotchbrite. Personally I would not touch the piston skirts if they are smooth and not scored and I certainly would not use 240-320 grit sandpaper. 003" is certainly far from being tight with a fresh rebore but it is certainly acceptable. The marks could be oil deposits, see if they wipe off, somewhat fresh hone marks are evident. If the bike ran good and did not smoke why did you take it apart? Oil leak or to see what makes it tick ?

[wmajinw]

If you cannot feel the  vertical marks with your finger nail I would not be concerned. Since the cylinders off I'd go a pass or two with the hone, very sparingly. Since the tech measured the piston skirt and the cylinder to arrive at the .003"clearance you might be able to do as he suggests to the skirts but very lightly with say scotchbrite. Personally I would not touch the piston skirts if they are smooth and not scored and I certainly would not use 240-320 grit sandpaper. 003" is certainly far from being tight with a fresh rebore but it is certainly acceptable. The marks could be oil deposits, see if they wipe off, somewhat fresh hone marks are evident. If the bike ran good and did not smoke why did you take it apart? Oil leak or to see what makes it tick ?

When removing a spark plug part of a thread came with it. Took apart the head to see if any thread fell into the cylinder.

[rotortiller]

Ideal time for a spark plug re-thread insert.

[Tracksnblades1]

UPDATE:

Got in touch with a local oldtimer who's been working on old bikes for a long time.

We checked the piston to cylinder clearances and all 4 were 0.08. Funny thing is that he said that you can tell if the clearances are ok by removing the piston rings and letting it from in the cylinder - how fast the cylinder drops usually tells if the clearances are ok. He did that with one of the cylinders and said that the clearance should be about 0.08 (this was before we did the measuring). I guess when you've been working all your life on bikes you catch on some tricks, but this was straight out like fortune-telling for me.

Anyway, he said that its strange that there are these streaks, because the engine looks like newly refurbished and the honing done on the cylinders is very good.

One thing he said that needs to be fixed is the pistons themselves. There's some smooth shiny spots on the piston skirts and he said that might be a problem, because oil won't stick to it, which could result in a seized engine. His advice was to get some 240-320 grit sand paper and just make a couple horizontal passes on the shiny spots to make some grooves for the oil to stick.

I thought Honda wants 0.02 - 0.04mm…

0.0031 thousands is wore out in my book if your pistons are cast Honda’s..
A brand new wiseco forged 550 piston recommended 0.002 with that tiny bore size..someone posted a while back..maybe calj737’s post, maybe not..🤔

[Tracksnblades1]

It was 737’s response with picture…

See link “reply #6… still says files to large bs..

http://forums.sohc4.net/index.php/topic,144157.msg1640247.html#msg1640247

[HondaMan]

I use 0.0006" to 0.0010" clearance for the 500/550 engines with cast pistons.

My own 750 (3rd oversize) has 0.0006" clearance with cast pistons. It runs cooler than it used to, has a higher top end speed, too.
When I rebuild 750s for others I use 0.0008" clearance with cast pistons.

[rotortiller]

Shop manual page 141 has the wear limits. Trust the old guy you spoke with, the engine is allowed to show wear and you are well under service limitations. If you took the largest new standard piston (2.301") and the smallest cylinder bore (2.303") the manufacturing tolerances would yield .002" clearance. If you took the smallest new standard new piston 2.300" and the largest standard cylinder bore 2.304" you would have .004" clearance. If you took the wear or service limits on the piston 2.302" and cylinder 2.307" the clearance would be .005".  In all cases you are still good, to me .002" is a good general clearance for that engine at rebore time using Honda parts. I tend to follow published engineering data and work the tight side hoping to extend wear time and avoid seizure.

[grcamna2]

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