Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: CB5501977K3 on January 11, 2020, 10:26:36 PM
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Hi All
I have now finished my top end rebuild and replaced all the gaskets and O ring seals but I didn't remove the valve guides so didn't replace the eight O ring seals which fit under the pressed in guide. (I did replace the valve guide seals and lapped in the valves)
All went well and components looked in good shape, bikes done around 15,000km (9500 miles) and spent it's life in South Africa. Barrels looked immaculate and no signs of ware or scoring and the engine reassembled well with a genuine Honda head gasket and all parts torqed back to specification.
The machine starts 1st or second kick from cold, has plenty of power and is running very smoothly and sounds like a sewing machine when ticking over.
The reason I am posting this query is that it suddenly seems to produce smoke out of all four pipes when the engine is working hard - say dropping down to 4th at 50 to overtake something. Once the engine has been taken off peak load it's runs clean with no exhaust smoke.
Could it be the valve guide O rings are shot, they were not disturbed during the rebuild but wondering what would cause this intermittent smoke. Could oil fumes or oil be coming down back into the air filter box somehow and burning via the emissions breather pipe?
I have 10/40 semi synthetic in with new filter - 3.2L
I have attached a couple of images to show pistons and barrels best I can.
Any thoughts appreciated
Chris
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Are there signs of oil vapour in the air filer and the sponge in the bottom of the air filter box?
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Never changed those O rings in my life unless replacing guides, from memory amount of oil seems high where is it on dip stick? Did you hone and re-ring if so what type of rings?
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Hi and thanks for the quick responses..........
I will check air filter for oil - good point Julie.
Re re rings Bryan, I didn't replace the rings and didn't hone. Before I took the engine apart it was not producing this smoke under load. The rings seemed rather gummed up before I cleaned and lubricated them. They moved more easily around the piston groove afterwards. I was careful to position rings back as per Haynes manual - so many degrees apart.
Compression feels good on kickstart and it starts well.
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I have now managed to attach a few images of the rebuild showing piston rings.
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On cylinder #3 piston, can I see damege in the way of bits missing above the top ring and on the top ring land? Could just be the photo though.
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Hi Julie
It's not damage, just a small carbon deposit probably or the light on the image.
Chris
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Hi Julie
It's not damage, just a small carbon deposit probably or the light on the image.
Chris
Ah, OK. So my theory on it, for what it's worth, is that the carbon you had was doing a good job of keeping everything as it should be but now you have removed the carbon, your piston to bore clearance is now to big and oil is getting by. What was your piston to bore clearance?
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There are a couple of possibilities,
Piston to bore clearance
Ring gap and/or orientation
Ring broken/distorted
Valve guide broken on assembly----easy to do if the rockers were not all held up when fitting valve cover
Wrong or too much oil(i have never used semi or full synthetic)
What colour smoke is it putting out? Blue, Grey, White
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On the ring orientation the rings go chromed in top groove, black in secong groove, oil scraper in bottom, all fitted with any markings(seen at ends) facing upwards.
I have seen the second ring fitted upside down and that will pump oil to the top of the piston, i have also see ring grooves worn excessivelywhich lets the ring float and gives the same effect.
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Hi Chris
I did a rebuild on a GL1100 back in about 1997 it had done 72k and was striped to replace the primary drive chain, All the shells were platiguaged and pistons bores etc measured and all came out within tolerances.
So I replaced primary chain brought all the gaskets o-rings damaged bolts were replaced , All the valves were lapped in valve stem seals replaced and then I decided before rebuilt to replace the crankshaft shells as they had light scoring but left the pistons and rings , Big Mistake!!
After the rebuild it all ran fine and sounded really sweet but on load going up hills or overtaking a plume of blue smoke could be seen behind it which was really disappointing after pumping about £1100 into it .
I then made tools to pressurise each cylinder with a compressed air source and remove springs etc so I could fit new valve stem seals in situ.
That didn't make the slightest bit of difference. It had to be the fact that I hadn't replaced the rings rebored etc , they were all perfectly clean but false economy in the long term.
Now wings are known to use a bit of oil and consumption wasn't high but embarrassing when out with other bikes.
John
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Many thanks for taking time to read my post and your suggestions.
This afternoon after Bryan's comment re my 3.2 litre of oil (it sounds too much) I checked the dipstick.
Why I didn't do this before I don't know but I carefully measured - I think, 3.2 after changing the oil filter. Anyway the level was far too high and well over the top mark position.
I have now removed around 600ml and level is midway not screwing the dipstick in.
I took the bike up my 20% gradient testing hill on Llandudno's Great Orme and no light grey smoke where there had been before.
The only thing I could think of initially was the O rings I hadn't replaced which were the valve guide O rings.
I just have the later type PD46A's carbs to get running correctly now but it's well on the way to running how I want it.
Regards Chris....
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Best of luck with those carbs
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Great news and a simple fix. You're not the first to overfill and you sure won't be the last.