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Valve Clearances

Discussion in 'Technical and Troubleshooting Torque' started by Seamus, May 28, 2005.

  1. Hello forum, :)

    What are the valve cleareances?

    The mechanic that just changed my rear tyre said after 24,000kms I (about now) I should get my "valve clearances" checked out.

    About a month ago I had the following service at 20,500kms:

    1/ Change Engine Oil;
    2/ Change Engine Oil Filter;
    3/ Change Transfer Case Oil;
    4/ 4 New Spark Plugs;
    5/ Replace Rear Brake Pads;
    6/ Replace Air Filter;
    7/ Remove Front Forks. Drain and Replace Fork Oil;
    8/ Grease Steering Head Bearings;
    9/ Fit Grease Nipple To Steering Head;
    10/ Adjust Steering Head Bearings;
    11/ Tune and Adjust Carby;
    12/ Remove Front Wheel Bearings and Re Pack - Grease;
    13/ Straighten L/H Front Disc;
    14/ Bleed Front Brakes;
    15/ Oil Clutch Cables;
    16/ Oil Accelerator Cables;
    17/ Adjust Clutch Cables;
    18/ Check Tyre Pressures;
    21/ Add Fuel Cleaner To Tank;

    Can't see any "Checked Valve Clearances" here. Is checking the valve clearances something only a mechanic should attempt?

    Thank you. :)
  2. Valve clearances are when your bike shop has overstocked on valves and decides to sell lots of them really cheap!!!
    Seriously, valve clearance is the distance between the top of the valve and the rocker that operates it, opening and shutting it to allow gases into and out of the combustion chamber.
    It is usually adjusted by placing thin metal plates called shims in between the valve head and the cam lobe. Because this usually involves taking the tappet covers off and removing the cams, it is usually best done in a shop. They will also have the correct thickness of shims to ensure that your valves are opening and closing the correct distance.
    If your valve clearance is too close (tight) this results in an engine being difficult to start when cold, though it CAN be started with generous use of the choke. The effect of the "tight" clearance in a running engine is that the valve is always "attacked" by the hot gases, without any opportunity to transfer the heat thru the valve-seat because of it's poor or no contact with it. Soon, this results in a burnt valve. Owwwww !
    Conversely, if the clearance is too loose, combustion will be adversely affected engine becomes very noisy, and performance suffers.
    Of the two, it's better for valves to be too loose than too tight, but, as modern engines are designed to operate on a knife-edge of tolerances in order to deliver best performance and reliabliity, ensure that your valves clearances are as the manufacturer recommends.
  3. Thanks rc36Honda, :)

    I don't know if it is the valve clearances but it takes a while for the engine to warm up. I have to pull the choke all the way out most times I start the engine. On a cold morning I stand around for maybe five minutes waiting for it to get warm. Ten minutes would be better but I don't wait that long.

    I used to ride off with the choke out and I'm told that was a big no no. On a mild afternoon like it is now, I'll still have to pull the choke out all the way.
  4. Yep, sounds like a trip to the shop is in order.
    You definitely should NOT have to ride the bike with the choke on.

  5. How often is the bike used? does it ever sit around for long periods?

    If the bike is cold, and you ride with the choke off, does it ride poorly at low revs, any particular rev range, or everywhere

    Does the engine ever make a ticking noise? when cold?

    If you have to ride with the choke on, it's running lean, which could mean bad carby tuning or dirty carbs (from sitting around, optimax, etc). Although you're due for a service, so valve clearance, carb sync etc might fix it.