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cam timing

Discussion in 'Tech' started by MXRACER70, Dec 29, 2008.


    MELK-MAN The Dude abides...

    .. then throw ignition timing into the mix based on what fuel you run...:confused:
  2. johnnycycles

    johnnycycles Active Member

    there are so many factors that go into an engine, you change one thing it seems like it affects 10 others!!! It is a never ending mission; its hard to find the perfect settings for everything. When you start changing things, you need to be able to measure a/f ratio, exaust temp at different spots on the exhaust, ignition timing, p/h clearance, p/v clearance, comp ratio, cam timing, knock sensors, valve spring comp, I could go on forever it seems. Fortunately for some of us we have the tools and the knowledge to do this and the others must learn from our mistakes / accomplishments.
  3. MXRACER70


    my pistons are 13.1-1 cr, stock cams and the head is stock hieght
  4. MXRACER70


    oh and i am a novice to street bikes, but i have been building 4 stroke atv engines that compete at a national level for 4 years
  5. Thug Life

    Thug Life My name is Chris!

    You seem very knowledgeable Johnny, I see you own a r-6 too, at what degrees do you check in/ex P-V? Just curious how YOU do it.
    Last edited: Dec 31, 2008
  6. johnnycycles

    johnnycycles Active Member

    Please don't flatter me, I'm nothing compared to some of the other guys on here. On every engine I do I always start at the stock cam timing, and go from there. If you want to change the timing one way or the other, you need to know where the bike is making it's power in it's power band, but then you are going to need to know what your p-v clearances are as well when the cams are degreed where you want them. You need to be on top of knowing what components need to be changed out on the motor and when. Say for instance you advanced the exhaust cam x degrees, and now your p-v clearance is y. If you spin a rod bearing the piston is possibly going to be able to make contact with that valve, where as at the stock timing position it wouldn't. You need to be prepared to pay the consequences and know all the other factors that come into play. Like these other guys have been saying, they don't just slap a thinner head gasket on there and call it a day and make tons of power. Bearings, valves, chains, pistons, rods, they all have to be monitored and changed out when their life is getting close to it's end. Everything inside the motor is connected in one way or another, so when one thing goes out, you have the potential to have EVERYTHING go with it.
  7. RM Racing

    RM Racing Tool user

    On the R6, start at 11 degrees BTDC on exhaust and 11 degrees ATDC on intakes. If it's the first time you've built the motor, it's a good idea to then check it at 10 and 12 to see if it increases or decreases. You want to find the minimum clearance. You may have to check it a few times to discover the trend. Once you know the specific combination on a particular build, you can usually count on the same crank position giving the minimum clearance. If it's really close to the minimum, some builders will check each valve individually. (Better than hitting stuff later)

    Or, you can stuff Silly Putty in there and turn it over like car guys (and old bike tuners) do... :rolleyes:
  8. davetlr

    davetlr Well-Known Member

    Please flatter me. If you are starting at stock cam timing, how are you checking p/v clearance?

    Obviously, you must not build or tune your own bikes.:wow:

    knock sensor on a bike?

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