TDCC is where you find it...

Discussion in 'Thumpers' started by creeper, Sep 4, 2005.

  1. creeper

    creeper Still alive...

    Joined:
    Dec 13, 2003
    Oddometer:
    10,718
    Location:
    Puget Sound
    Mornin' folks... 'er, maybe afternoon or good evening... whatever.


    I've had a few midnight e-mails, PMs and phone calls over the past few months from folks having "issues" with their first time inspecting/adjusting their valves on their LC4's and other bikes as well.

    I think once they are in the right place, everything goes fine... it's the "getting to the right place" part that seems to be a bit of a concept to grasp.
    So, bearing that in mind, I thought that a little overview of how a 4-stroke, single cylinder engine works and the relationship to valve lash inspection might be useful to a few peoples.

    If you already know how things work... move along, nothing to see here. :mulie

    This method of finding TDC-C applies to all 4 stroke singles. KTM, Husqvarna, Gas Gas, Sherco, Beta, Husaberg, HRC-Montesa... and all Japanese thumpsters too.


    ____________________________________________


    TDCC is where you find it.

    A 4-stroke engine is composed of 4 strokes, 4-cycles, 4 events, 4 call them what you will... things where shit happens.

    A piston is attached to a connecting rod, which in turn is attached to a crankpin, which in turn is attached between two flywheels in an offset position from the centerline of those flywheels. As the flywheels turn round and round... the piston goes up and down.

    Everything is measured in degrees of flywheel rotation... as in one downward movement (stroke) of the piston equals 180° of flywheel rotation. A following upward movement of the piston equals another 180° of flywheel rotation... for a total of 360 degrees of rotation, or one complete turn of the flywheels.

    In a 4-stroke engine, there are 4 "events". I like to call them events sometimes because that reduces the confusion associated with the terms stroke and cycle. They are intake, compression, power and exhaust.

    In simple terms, each event occurs during an upward or downward stroke of the piston... the reason a 4-stroke engine is called a "four-stroke" engine.
    Each event requires 180 degrees of flywheel rotation, so for all four events to occur, the flywheels must rotate two full revolutions... 4 events X 180° = 720 degrees of rotation.

    When a piston reaches the exact top of its stroke, it's called Top Dead Center... when it reaches the bottom; you got it, Bottom Dead Center. Remember this... there'll be a test later. :nod

    Now, let's bring the valve train into play. For a 4-stroke engine to work, we need fuel, compression and spark. We'll save the details of the spark part for another day.
    To get a combustible fuel mixture into the cylinder, and the combusted mixture out of the cylinder, we need valves.
    The valves have to open and close in time with the relative location of the piston... and like the piston itself, the opening and closing of the valves is measured in degrees of crankshaft rotation.

    In a simplified engine, it goes like this:

    1. The intake valves open at TDC-Intake, on the intake stroke
    and closes at the bottom or BDC-Intake. There's 180°.

    [​IMG]

    2. The valves are closed on the compression stroke. There's another 180°, and we've completed one revolution.
    [​IMG]

    3. When the piston is near the top of the compression stroke, or TDC-Compression, a timed spark occurs and now we begin the power stroke. The valves continue to remain closed.
    4. The power stroke moves thru its 180° of flywheel rotation.

    [​IMG]

    5. At the bottom of the power stroke or BDC-Exhaust, the exhaust valves open and remain open all the way back up to TDC-Intake, where the whole thing starts over again... There's the last 180°, and now we've completed the 720° of crankshaft rotation in our simple 4-stroke engine.
    [​IMG]

    6. Ta Da! :clap


    Event numbers 2 and 3 are the ones you need to look at when locating TDC-C for the purposes of valve inspection and adjustment.
    In a real engine, valves do not open and close at TDC and BDC... they open before and after these reference points to accommodate the realities of pressure and velocity.
    It is for this reason you must be very near TDC-C to ensure that both intake and exhaust valves are at a complete rest and all valve lash is present and accounted for.



    Now, knowing what we know, let's find TDC-C.

    Remove the spark plug so that the engine can be turned over more easily.
    Remove your rocker or cam covers so that you can see the valve actuation as it occurs.
    Shift your transmission into top gear and lift your rear wheel off the ground.
    Turn your rear wheel slowly in the normal direction of rotation and watch the valve actuation.


    It is not necessary for you to continuously turn the rear wheel... you can stop any time you feel the need, and start again when ever the mood strikes.

    When you see the intake valve actuation... the valves pushed down into the combustion chamber, then allowed to close, you are at the end of the intake stroke and on the compression stoke. If you went too fast and too far, you went right past the TDC- Compression stroke and are now somewhere on the power stroke... oops. :huh

    How do you know you are on the compression stoke? This is where a soda straw comes in handy.
    Inserting a soda straw into the spark plug hole allows you to see the movement of the piston in relation to the valves.
    If the intake valves have closed and the soda straw is climbing out the spark plug hole, you are still moving up to TDC-C... good for you! :thumb

    Slowly bump the rear wheel and watch that soda straw, it rises bit by bit until the piston reaches TDC-C... when it stops moving upward, this is as close to TDC-C as you will ever need to be to inspect your valve lash.

    Oops... the soda straw is starting to go down the hole! :eek1 Can I back up the rear wheel a bit without going around again?
    Yes, you can... if you really have a good idea where you're at. If not, it's not going to kill you to go 'round one more time. Pull the soda straw out of the plug hole and reinsert it after the intake valves have just closed... unless you enjoy watching your engine eat soda straws. :nod... :nono



    On most engines, for the purposes of valve adjustment, all you have to do is be close to TDC-C, not exactly right on it. If you read the description of the simplified engine, you see that after the intake valves close, the exhaust valves don't open until near the end of the power stroke.
    If you can be within less than 8mm of piston travel, on either side of TDC-C, you should be good to go.

    I think that should do it. I hope I've been able to explain this in simple enough terms that anyone who owns a tool set and motorcycle, and wants to attempt their own valve lash inspection/adjustment can do so.

    I've linked this post to the original valve lash inspection/adjustment post.

    Creeper

    To print a copy of this guide, go to the top of the page and click on "Thread Tools" then click on "Show Printable Version"


    Oh... to what ever person did these illustrations on the website I stole them from 6 months ago... thanks, I knew I'd use 'em sooner or later. :D
    #1
  2. motu

    motu Loose Pre Unit

    Joined:
    Dec 28, 2001
    Oddometer:
    5,399
    Location:
    New Zealand
    I learnt to set tappets on real singles - a Goldstar has 120deg of overlap,so you have to make sure you are on the back of the cam to set clearance,here's the little formula....

    When the inlet valve has just closed,you set the exhaust valve....when the exhaust valve is just opening,you set the inlet valve.I have never used TDC to set valves,I always set on the back of the cam.
    #2
  3. creeper

    creeper Still alive...

    Joined:
    Dec 13, 2003
    Oddometer:
    10,718
    Location:
    Puget Sound
    Nothing wrong with that. It works fine and if it works for you... groovy. :thumb

    As I said in the beginning, if you know how things work already... move along.
    This is for people that are doing it for the very first time and are already a bit nervous and stressed out about it.
    It has as little information as possible about how real singles work to avoid any additional confusion.
    It's not intended to demonstrate how much I know, but rather just enough to do the job correctly.

    Understand the concept motupaika?
    #3
  4. ktmnate

    ktmnate Long timer

    Joined:
    May 7, 2003
    Oddometer:
    3,091
    Location:
    Somewhere
    Wow Creeper! Glad to see that you havn't lost your teaching skills.



    Nate
    #4
  5. Darin

    Darin WYSIWYG (WIZ-zee-wig)

    Joined:
    Mar 1, 2004
    Oddometer:
    594
    Location:
    Retired military lounging in FresYES
    It's my turn......:norton

    ...by that I mean Monday morning (hope it's not raining) I'll be saving myself $138.00 and doing a valve adjustment. Am I nervous? --not really, it's just time consuming to remove all the components to get to the task at hand.

    Ok on to better things....now where is that Toxic Brintney thread at?:evil
    #5
  6. creeper

    creeper Still alive...

    Joined:
    Dec 13, 2003
    Oddometer:
    10,718
    Location:
    Puget Sound
    Thanks Nate... that's a very kind compliment considering I haven't taught in 3 years.

    There are so many levels of understanding... and it's not like a mechanical degree is a prerequisite to enjoying and working on motorcycles... but it sure helps to be able to do the basics.
    I guess the original guide left a few people in the lurch, so I took it down to a more elemental notch.


    Darin dear... don't fuck it up. :nono You'd only have 3 days to unfuck it. :evil
    #6
  7. Darin

    Darin WYSIWYG (WIZ-zee-wig)

    Joined:
    Mar 1, 2004
    Oddometer:
    594
    Location:
    Retired military lounging in FresYES
    If I do it's all your fault :patch and will be calling yea
    #7
  8. creeper

    creeper Still alive...

    Joined:
    Dec 13, 2003
    Oddometer:
    10,718
    Location:
    Puget Sound

    At no time do you see me twisting your arm. Go ahead and spend $138 at your local KTMest... he could prolly use the cash. :evil
    #8
  9. motu

    motu Loose Pre Unit

    Joined:
    Dec 28, 2001
    Oddometer:
    5,399
    Location:
    New Zealand
    It was one of the first things I learnt to do on my bike - at 17 the first lessons learned go in deep.I may of not known how the motor worked,but that little rule has stayed with me all these years.
    #9
  10. dagwood

    dagwood Banned

    Joined:
    Aug 25, 2003
    Oddometer:
    35,427
    Location:
    Vancouver, Not! BC...
    eh hem...
    side note; don't blindly follow the (KTM) manual either. the crank locking bolt can be installed 180 out.
    don't ask how i know this but follow Professor VonCreepers advice. works every time. :bow
    #10
  11. Renazco

    Renazco Formerly AKA Boejangles

    Joined:
    Apr 17, 2003
    Oddometer:
    4,750
    Location:
    Santa Rosa, Ca.
    I call Creeper "Doc" for a reason,,, Doc's the man!

    Thanks Doc! this place isn't the same without your help around here, in fact your insight and help reminds me of what this place used to be like around here at one time :nod
    #11
  12. creeper

    creeper Still alive...

    Joined:
    Dec 13, 2003
    Oddometer:
    10,718
    Location:
    Puget Sound
    Know exactly what you mean... I had a '56 Panhead scattered all over my dads garage at 15... not a clue as to the theory of how it all worked, but when I put it back together and it ran... that was good enough for me.

    On a Harley, the lesson I learned from an old Hells Angel was when the front intake was open, you adjusted the rear intake pushrod so that you could turn it with just a bit of drag, and so on and so forth 'til done... I can still do the damn things blindfolded.
    #12
  13. creeper

    creeper Still alive...

    Joined:
    Dec 13, 2003
    Oddometer:
    10,718
    Location:
    Puget Sound
    Watch it SeatMan... yer' gona' make me all verklempt 'N shit. :cry
    #13
  14. motu

    motu Loose Pre Unit

    Joined:
    Dec 28, 2001
    Oddometer:
    5,399
    Location:
    New Zealand
    Like setting Triumph intake tappets - just using your fingers to waggle the rocker,at 1.5 thou you could ''hear'',but not feel the clearance,if you could both hear and feel,that was 2 thou,clearnace you could not hear or feel was below 1 thou - impossible to tell someone how to do it,it just has to be done enough times to become second nature...I can't ''hear'' my wife anymore,let alone Triumph tappets....
    #14
  15. ChrisC

    ChrisC Amal sex?

    Joined:
    Feb 25, 2003
    Oddometer:
    6,321
    Location:
    Prescott, Arizona USA Earth
    Some call him Doc, others say Dick, my fav is Dork....to each his own :freaky
    #15
  16. creeper

    creeper Still alive...

    Joined:
    Dec 13, 2003
    Oddometer:
    10,718
    Location:
    Puget Sound

    They call me Dr. Dick... Dr. Dick Dork. Sounds like a porno name to me.
    #16
  17. markjenn

    markjenn Long timer

    Joined:
    Nov 9, 2003
    Oddometer:
    10,648
    Location:
    Bellingham, WA
    Nice writeup Creep.

    I thought I'd add that although I don't think it is critical to get the engine precisely at TDC-C (typically done with crank markings), you don't want to be totally cavalier about it - get it close. As Creep says, while there is a fairly large interval between when the intake valve closes and the exhaust valve opens when both valves are closed and clearances can be measured, the cam base cricles (the part of the cam lobe without the "bump") are not perfectly round by any stretch. I've commonly seen variatiions of .001 to 0.0015 inch in the base cricles. These variations in the base circles cause the measured valve clearance to vary depending on where you have the cam on either side of TDC-C.

    I first noticed this when is was doing a valve adjust on a Kawasaki ZRX (which is basically a ZX-11 motor). When I did the valve clearance check the first time, I just bumped the engine around until the cam lobe of the valve I wanted to measure was pointed directly away from the valve, without paying any attention to TDC. Using this method, 10 of 16 valves were out of spec and required re-shimming. But when I did it "by the book" with the engine precisely at TDC, 8 of the 10 valves which out of spec were magically within spec. This was because of the variation in the cam's base circle. I could have adjusted all the valves using the first method and the motor would have been fine, but by doing it the way that it was done at the factory (or the way it was done at the last adjustment) I didn't chase the random variatiions in the base circles of the cams.

    And it's variances like this that make ultra-precise valve adjustment, while certianly harmless, relatively pointless. If a valve is in spec, leave it alone. If not, adjust it. But tearing your hair out to get each valve precisely in the center of the range or precisely the same as the next is computing something to eight digits of precision when your starting data only has two.

    - Mark
    #17
  18. creeper

    creeper Still alive...

    Joined:
    Dec 13, 2003
    Oddometer:
    10,718
    Location:
    Puget Sound
    Some very good things to ponder Mark...

    Sometimes I wonder if all the modern complexities are worth the result. Technology for technologies sake and all that. I guess if I worried about it too much, I'd go be a Quaker. :huh

    Maybe that's one of the reasons LC4 engines appeal to me... they're a little stone age compared to the latest trickiest disposable engines, but I like old designs with decades of evolution and repetition induced durability.
    #18
  19. potatoho

    potatoho Cheese and Rice!

    Joined:
    Aug 3, 2004
    Oddometer:
    4,709
    Location:
    Sea-level
    Ha! I just went through that with my lumpy G1 cam. I had been using the shortcut method of setting them on the heel rather than at TDC-C. Always fine with my stock LC4 cam, as I compared the measurements the first time I adjusted my valves. When I installed the G1 I didn't bother to check for differences, and it turns out that the heel measurement on the exhaust lobe is quite different than at TDC-C. Using the heel method, I'd been setting them too tight!

    Do all LC4's have the window in the side cover? I was surprised at how easy it was to find exact TDC by looking in the window for the timing mark.
    #19
  20. braaap!

    braaap! Long timer

    Joined:
    Mar 16, 2005
    Oddometer:
    2,818
    Location:
    Here and There
    Gob shut, listening hat on (save page as: Creeper_LC4_Valves 101)

    gracias Mr creeper :feelgood

    not in a :ymca way but.......
    #20