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For the preservation and enjoyment of 1928 to 1931 Indian Scout Motocycles
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alot of grey smoke coming from exhaust

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  • 26 Jun 2020 4:06 AM
    Message # 9061566

    Recent have noticed a significant amount of grey exhaust coming from bike> 
    Oil level was checked, about one once comes out each time. I have checked it multiple times.  Oil is black in color.  I adjusted the oil pump by turning it clockwise in about one half a turn.  The problem remains.  The engine seems to be working well and acceleration remains strong.  

    Any ideas, oil rings on my cylinder?
    Will I hurt the engine by continuing to run the bike?
    Further adjustments to the oil pump?

    Thank you, 

  • 26 Jun 2020 7:53 PM
    Reply # 9063176 on 9061566

    Hi Marc, further details might include:

    - fresh rebuild?

    - miles on your motor?

    - anything newly done to the motor or exhaust or fuel tank?

    And then is it grey smoke, or more with a bluish look to it?

    You may be looking at something normal...or not!

  • 27 Jun 2020 3:10 PM
    Reply # 9064373 on 9061566

    Yes, I agree with Harry, better help if as much data possible is provided with the question.

    I would not adjust the pump down any more when you already have a correct oil level with just an ounce of oil coming out. Check that regularly and don't let it be less. 

    Check the plugs for unequal colour. If both have same colour then it maybe, probably, hopefully isn't trouble with rings, the smoke can be caused by the petrol quality if it contains ethanol and water.

    You can do a quick diagnostic leak down check, just make an old plug or two with a hose so you can put some compressed air in, just not too high pressure, in the cylinders one by one and listen in the ventilation tube, exhaust and carburetor for equal sound of air passing through. Recording the sounds with the cell phone, if possible, is a great help. That recording can be stored for later comparison.

    The pistons should be about in top dead center on compression stroke, easily checked with a thumb over the plug hole and turning the wheel with the gearbox in third. Don't forget to lock the rear wheel before applying air pressure.

    Last modified: 28 Jun 2020 6:28 AM | Carl-Erik Renquist
  • 28 Jun 2020 12:52 PM
    Reply # 9065804 on 9061566

    Thx for the responses.  Harry and Carl-Erik

    I did run this by Randy Walker who has done some top notch work on the bike more recently. 

    The exhaust is more white grey not bluish. 
    Engine has not had recent work on the top and bottom. 
    Work was done on the transmission and clutch recently, doing well.

    Miles on the bike, unknown. But a lot, belonged to Ben Chesney

    Nothing new done on the motor, fuel tank or exhaust.

    I will not adjust the oil pump anymore and will keep an eye on the oil level. 

    Rebreather valve was recently fixed a few months ago.   When repaired the rebreather was heard as a wheezy sound.  This sound was heard right after  I attempted to kicked the engine over, but was unsuccessful in starting the bike. However recently I can not hear this rebreather sound.  

    Spark plugs changed a few weeks ago and now appear with heavy carbon.  Both plugs look the same color and equal amount of carbonization.  This has happened over a few weeks of use. 

    Bike rides well with good and strong acceleration through all gears. 

    Also, was having trouble starting the bike, usually starts in three to four kicks.  So I had the carburetor cleaned  about a month ago (it was quite dirty) and right after cleaning it started easily with a few kicks.  However, again more recently having more trouble kick starting the engine.  


    1).  Could it be the petrol I am using?  (too much ethanol and or water)?  I use lowest grade regular at my local gas station.  Is there a particular brand, company or grade I should consider?  Should I be adding something to the petrol I put in my tank?

    2).  May I ask, is the ventilation tube the same as the rebreathe valve?  When working should it make a wheezing sound?

    3). If the spark plugs the same color (carbonized), does this rule out cylinder oil rings needing repair?   

    4).  Could the problem may be with the oil pump needing work? To much oil returning to the engine?  

    5). As the engine runs strong and accelerates well, does this rule out cylinder problems?

    Thank you, for any responses,

  • 29 Jun 2020 9:48 PM
    Reply # 9068780 on 9061566

    I just had an idea, it might be that the petrol has started to leak into the oil tank! Check that pronto, empty the oil tank, fill the gas tank full, leave it overnight and observe if it is seeping in petrol in the oil tank. It is very harmful for the engine to run on oil that is diluted with petrol!

    If you should find that for a fact, then be sure to open up the oil pump the half turn you previously reduced before you run the engine again, as diluted oil is thinner runs right through the pump and consumed in the combustion chamber. 

    Last modified: 29 Jun 2020 10:34 PM | Carl-Erik Renquist
  • 30 Jun 2020 7:27 AM
    Reply # 9069366 on 9061566

    I go on with other hints and tips for your other questions.

    1) As you have had recently clean the carb and found dirt, I would remove the tank and clean it, petcock and line thoroughly however industrious and hard job that is to make good. Final rinsing can be done hose down with water, just rinse with denatured spirit or ethanol to soak up the last of the water. And then try with a tank of fresh premium gas without any additive. Preferably non ethanol. Or you can run the bike with an auxiliary tank that is clean, just for test purpose.

    The engine should run just fine with lowest grade regular, it is just that lowest grade might be slush quality with whatever settlings that the petrol company wants to get rid of.

    2) At the base of the breather tube is the rebreather valve, it is just a flat disc that is oscillating back and forth with the air flow that the pistons make when they go up and down. Normal is a pulsating or fluttering sound from the tube.

    A wheezing or whistling sound signals that the disc is stuck. That is upsetting the lubrication system and needs fixing without delay. Just remove the tube and clean the seat and disc. No gasket, just a thin smear of (anaerobic) sealer or at the most a very thin paper gasket should be used between the tube and crankcase because the disc can/will hang up in the gap between the housing and crankcase (or cam cover), that the gasket makes. It can be fiddly but a dab of grease will hold the disc in place in the tube seat, at reassembly.

    1928-29 engines has a second breather valve disc inside the cam compartment, the housing is different and they don't tend to stick. A gasket there must never be used.

    3) Same colour plugs does not rule out ring problems, unequal colour would indicate problems with one cylinder. Today's ethanol blended gas does tend to show much paler/whitish deposits and not leave a clear colour based indication so diagnosis based on colour is a lot more difficult. Mistakes can be done taking white or transparent deposit for a lean carb setting or manifold air leak.

    However, heavy (black) carbon on the plugs is always from oil passing rings or valve guides. Beige/brownish carbon on the plugs is more normal. If that turns to (greyish) carbon or clean wet plugs, that can indicate excess fuel. Something wrong with the carburetor or a poor magneto that is missing ignition because of weak sparks. I'd say it again, with the modern petrol it can be difficult to read spark plugs.

    4) If the oil level is OK in the crankcase then there is no reason to adjust anything on the oil pump. There is very little or no service job that can be done on the pump. The -31 pump has a few more details that might need an overhaul.

    5) I would do a leak-by test with compressed air as suggested earlier, that would expose worn rings or other leaks right away. A compression test will compliment the leak-by for a good diagnose. A weak magneto can make decent sparks at higher revs, so the engine might feel "strong" through the gears but hard to start.

    Last modified: 30 Jun 2020 7:48 AM | Carl-Erik Renquist
  • 30 Jun 2020 9:27 AM
    Reply # 9069622 on 9061566

    Carl-Erik's list is good as usual! 

    In a water cooled engine of course, white smoke can indicate water vapor due to some source of water in the combustion chamber (e.g. cracked liner or head gasket failure), and in an air cooled engine any water in the combustion will have to come from water contaminated fuel or oil, often through condensation in the fuel tank or oil tank.  But with your sooty plugs it's hard to think water is the issue, so perhaps it's a different contaminant?

    Last modified: 30 Jun 2020 9:28 AM | Harry Roberts
  • 30 Jun 2020 9:55 PM
    Reply # 9070857 on 9061566
    Tim Raindle (Administrator)

    Carl-Eriks suggestion about gas in the oil is a possibility. Seen it happen 3 times on runs,  excessive smoke also usually accompanied by oil leaking out from just about very possible orifice, as the oil gets thinned down by the gas.

  • 30 Jun 2020 10:01 PM
    Reply # 9070862 on 9061566
    Tim Raindle (Administrator)

    Also agree with breather comment, wheezing not good, ideally more of a twitter, a little like a ticking over BSA Goldstar :)

    You can check if its working fine by putting a length of plastic tube ( oil or gas line ) over the end of the breather pipe when the motor is not running, and sucking and blowing . You should be able to feel the disc closing and opening. 

    Don't use a gasket under the breather, it creates a gap thick enough for the disc to stick in, a thin layer over yamabond or similar should work fine.

  • 31 Jul 2020 4:37 PM
    Reply # 9137682 on 9061566

    Agree with likelihood of fuel entering oil compartment of tank.  Old original tanks are silver soldered.  Silver solder becomes brittle with age, making the seems susceptible to fractures., which allow fuel to pass into the oil tank.  
    Test as Carl Erik suggested.  

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