Smokey Exhaust again
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Thread: Smokey Exhaust again

  1. #1
    Member voxy53's Avatar
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    Smokey Exhaust again

    Hi All
    I posted a thread back in September last regarding my smokey exhaust on my rebuilt CB175 K6
    I decided to rebuild the engine again
    I stripped it down and had the barrels rebored +0.75mm and got new pistons and rings to suit
    I cleaned the head and valves and had two new valve guides put in the head (inlets) and the exhaust
    valves checked for slop which the engineering shop said were fine
    I put it all carefully back together.
    Started it up and NO smoke until it warmed up. It then started to smoke a little. I assumed it was just the assembly lube !!
    I took it for a 6 mile run round the town and found it was smoking on tickover a little
    I have now done a 25 mile run keeping below 6000 revs and not lugging it
    Smoking again but not as bad as before at this stage !
    I pulled the plugs and did a compression test. 165psi on both cylinders (new compression tester)
    I have just got back from a run of 54 miles and at tickover it smokes. Also up a long hill of approx. 11/2 miles it left a trail
    of smoke
    I have just checked the oil level and it is half way between the max and min marks !
    Interestingly there is a drip of oil at the end of the oil breather pipe (new rubber pipe)
    Is it possible that the head cover is blocked (although it has been cleaned at the first build stage) and
    is building up pressure in the crankcase and blowing oil out past the rings into the combustion chamber !!
    Any thought would be appreciated
    voxy53

  2. #2
    Senior Member mike in idaho's Avatar
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    Are the plugs oily or normal appearance? If the plugs are normal, pull the exhaust pipes off and check out the backside of the valves for evidence of oil leaking around the stems or around the od of the guides. If the plugs are oily, pull the carbs and check out the intake valves also.
    '65 YG1
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    My company car is a Kenworth

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    Member voxy53's Avatar
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    Hi mike
    I will have a check today but I suspect the plugs will be oily as the end of the exhausts are black and oily !!

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  5. #4
    Senior Member drydreamer's Avatar
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    If the engine was passing an amount of oil before, the exhaust may have some oil still in them, or a layer of oily carbon ala 2 stroke. Maybe this is what you are seeing, this "oily deposit" being burnt off??

    I assume the pistons etc where oe not pattern ones as some of them can be "oil passers/pumpers". As long as the engine is not overfull ( any oil baffle plate in the sump on these, will check cmsnl ) and not too much oil is being flung from the big ends etc., and the rings are on the right way ( not upsidedown ), and the valve guides are good, and the crankcase ventilation system is all good, it may be just oil useage which will settle after a good running in?

    How are the plugs, are they oily? and are the correct grade? I assume you do not add oil to the fuel.
    Rob Axel likes this.

  6. #5
    Senior Member drydreamer's Avatar
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    See cmsnl exhaust valve seals, some o rings involved....only limited time for a quick look on cmsnl, no oil restrictor jets seen, you have a lub diagram for thios engine??

    is there a breather hole close to the rwear sprocket on these ala c90, its been a long time.......and i assume the head gasket is good as the cmsnkl exploded views seem to suggest the rear outer head studs are oilways to the head??

    Again, littlehampton is in uk? i assume,,,,cb175k6 ss england?
    Last edited by drydreamer; 02-23-2019 at 04:04 AM.

  7. #6
    Member voxy53's Avatar
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    Hi All
    Do you think that a thicker oil may help ? Perhaps 10W-50 !!

  8. #7
    Member voxy53's Avatar
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    Hi All
    I seem to be having a problem replying to this thread
    I used genuine pistons and rings when assembling with the writing on the rings uppermost
    I spent some time today checking the tappets, adjusted the cam chain and checked the compression after the 54 mile
    run yesterday. 165psi on both pistons
    The exhaust did have oil in from the previous build but should have burnt off by now
    The plugs are oily and black
    I started the engine up today and there was no smoke until it warmed up then it started at tickover
    Blipping the throttle produced more smoke
    When I switched off for a while and started it again no smoke for a while until it got hot
    Oh and I don't put oil in the fuel
    Pulling out the dipstick and you can get a rush uf air which I suppose is normal, also the breather pipe
    blows air so is not blocked
    Any ideas ?

  9. #8
    Senior Member Rob Axel's Avatar
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    I'm your huckleberry...

    What's a "tickover"?
    "Yes, my hands and nails have grease stains. I ride vintage!"
    -xulf13-

  10. #9
    Senior Member mike in idaho's Avatar
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    You could place a check valve in the breather hose, that will create a small amount of vacuum in the crankcase to keep oil from running down the valve stems or past the rings. what does a Brake Booster Check Valve actally do? | Yamaha XS650 Forum
    '65 YG1
    '65 CB160
    '66 CL160
    '67 CL77
    '68 TR6
    '69 T100R
    '69 T120R
    '72 Commando 750
    '78 XS650E
    '79 Gl1000
    '81 440 LTD
    My company car is a Kenworth

  11. #10
    Member voxy53's Avatar
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    Hi
    Thanks for the replies
    Tickover may be a UK term but basically the engine speed with no throttle input
    Also, yes I do live in the UK on the south coast

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