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Valve timing question (with pics!)

Discussion in 'The Garage' started by KentMoney, Oct 11, 2011.

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  1. Jimmy650

    Jimmy650 XS650 Member

    Thanks for your reply, we already tried the second rotor position and advancing/retarding the trigger plate but still not running... Will keep trying
     
  2. Brian902

    Brian902 XS650 Junkie

    mrriggs/grizld1

    Why is it

    "Subtract open/close even closest to TDC, 133 - 25 = 108"


    When you degree a cam?
     
  3. mrriggs

    mrriggs XS650 Junkie

    Because you are trying to find the distance of the lobe center from TDC.

    When you divide the duration by 2, you know the distance of the lobe center from the opening and closing events.

    The intake valve starts opening before TDC and the intake center is after TDC. So you need to subtract the open-distance-from-TDC from the center-distance-from-open to determine the intake center-distance-from-TDC.

    Same thing with the exhaust except you will use the closing event since the exhaust center is before TDC and the closing event is after.
     
  4. Brian902

    Brian902 XS650 Junkie

    Just because I'm curious and because this begs the question,

    Why from TDC?

    Why not just use the lobe center from the open close event calculation.
     
  5. mrriggs

    mrriggs XS650 Junkie

    Maybe I'm not understanding the question so bear with me.

    The point of degreeing a cam is to verify that the cam is timed properly to the crankshaft. The degree wheel is calibrated to TDC on the crankshaft because it is the most convenient and relevant. Calculating lobe center from open/close events is meaningless until you reference it to the crankshaft [TDC].
     
  6. Brian902

    Brian902 XS650 Junkie

    Bingo!

    I was so focused on the cam and it's opening and closing and then finding the mid point that I was ignoring the relationship with TDC. DAH!!!

    Thanks a lot, it's great that even my stupid questions can be answered.

    It will be more fun this winter when I go through this 'degree the cam' process knowing I have no doubts as to why and how it is done.

    Lots of valuable resources at this site.

    Thank you mrriggs.
     
  7. KentMoney

    KentMoney XS650 Addict

    Degreeing your cam, although intimidating with all the number and special tools, is actually quite simple! and when you accomplish it you'll feel like a genius :)
     
  8. gregoryp

    gregoryp XS650 Enthusiast

    I've run into a similar issue. I have a rephased 81 engine that I put back together over a year ago, but finially getting the rest of the bike finished. Now trying to get the motor dialed in and ready to ride. I have a Hugh's cam and crank and a Pamco ignition. When I checked the ignition timing I had to fully retard the Pamco to to get the left cylinder to 15 degrees. When I checked the right cylinder (made a separate TDC mark on the stator for that side) I'm getting a reading around 25 degrees. I only have marks at 15 and 40 degrees, so the 25 is a guess. I assembled the Pamco per Hugh's blog on how to do it and he said the magnets should be horizontal, sort of at 10:00 and 2:00 when installed properly. Mine were sligthly rotated counter clockwise, not much but a little. I can post picture later when I get home. Then I read this thread and decided to check the lobe center to see if my cam was maybe off by a tooth. I set the vavle lash at 0.012" per the clymer manual and put a dial indicator on the intake spring retainers. My calculations are as follows:

    Left Cylinder - Open 32 BTDC, close 64 ABDC

    32 + 64 = 96
    96 + 180 = 276
    276/2 = 138
    138 - 32 = 106

    Right Cylinder - Open 31 BTDC, Close 61 ABDC

    31 + 61 = 92
    92 + 180 = 272
    272/2 = 136
    136 - 31 = 105

    Based on that it looks like the cam is in the correct position.

    I'm not sure why i would get different timing reading between the two cylinders, doesn't seem like that is possible? Also why would I need to fully retard the timing if the cam is dialed in correctly? I had the Idle low enough, so it doesn't seem like I'm getting any advance and when I rev the motor the left cylinder advances to 40, so that all seems ok.

    I know there are a bunch of ways to setup the Pamco, so I'm hoping I missed something and just have that wrong. Don't really want to have to pull the motor out of the frame and take it apart to change cam timing.

    When I first set it up I put the degree wheel on and rotated the motor until I saw a spark and indicated the position at which that occurred. From what I remember that seemed to work. Then I saw Hugh's blog and figured I would just follow that instead to make sure it was right. It's been a while and I do believe I changed something from my original setup, so maybe I should have left it alone:doh:

    Any guidance you could provide would be great.
     
  9. KentMoney

    KentMoney XS650 Addict

    so, are you able to get the engine to idle correctly? And you're saying that the timing light even shows that the ignition advances at higher revs?


    Have you tried simply just switching the magnet rotor to the other available slot and giving it another shot?

    Best,
    Kent
     
  10. gregoryp

    gregoryp XS650 Enthusiast

    Yes, seems to run fine in the stand. Haven't ridden it though as the rest of the bike is not quite finished. I have not tried switching the rotor position, but will check it out. When you rev it up you can see the ignition advance while watching with the timing light.
     
  11. KentMoney

    KentMoney XS650 Addict

    Hmm, i'm not exactly sure I understand the problem you're having.


    Degreeing a cam is basically ensuring that your valves will be opening and closing at the correct time in the combustion cycle.

    Ignition timing is making sure that the spark ignites at the correct time in the combustion cycle.


    You say your motor is idling and advancing as expected? So what's wrong?
     
  12. gregoryp

    gregoryp XS650 Enthusiast

    Here are the problems/questions I have.

    It appears that the cam lobe centers are correct, but I'm not 100% sure that the 106 specification is the correct value, so I wanted to confirm that. I retested it last night checking them with zero lash and at 0.050" of lift, which is supposed to be a more accurate way. It seems that it is since I did each one twice an got the exact same values. But I did get 104 for the lobe center this time.

    If I check the valve opening according to the clymer manual I get different values, but in one section it says to set the lash to 0.012" and the intake should open at 47 BTDC, which I don't get when I use that method, think I'm getting 32 from what I remember. But under specifications I think it lists 35 or 36 BTDC, but I'm guessing that is at the 0.002" of lash. Changing the lash makes a big difference in where the valves open and close. So I would like to confirm the correct lash settings and valve opening positions for degreeing in the cam.

    The bigger part of my problem and the reason I started digging into this is that when I put the timing light on the motor I had to fully retard the ignition to get the left cylinder to fire at 15 degrees. Then when I checked the right cylinder it was was firing at 25 degrees. The advance mechanism does work, so I was just providing that information to eliminate an issue with the advance mechanism causing me to have to retard the timing to get it correct.

    I don't understand how the timing values for the two cylinders could be different. I double checked both TDC marks using a piston stop, so I know my TDC is correct for both cylinders. I don't want to run one cylinder with the correct timing and have one to far advanced and cause problems.

    Just feeling like I'm going around in circles and want to finish the bike so I can ride it.
     
  13. KentMoney

    KentMoney XS650 Addict

    Mr. Riggs said the lobe center is 106 but that article on the first page said it was 107.5. Either way, you are at 104 so you are pretty advanced on your valve timing.

    So, you had to retard your ignition significantly to get it to idle? Perhaps you are compensating for the advanced valve timing and the solution is to replace the chain on your cam sprocket and get the valve timing right.

    Also, with a rephased cam shaft you shouldn't have to worry about the other cylinder not being correctly timed. If you focus on the left cylinder, the right cylinder will be correct as well. They have different timing because they are rephased, right?
     
  14. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Just a thought. There's also a 270° version. Wonder if you got a part mix-up...
     
  15. gregoryp

    gregoryp XS650 Enthusiast

    I think I am going to try and rotate the cam gear and get my cam timing correct and then go from there. Need to solve one problem first. As far as the rotor goes, I'll have to look into that and see if it could be the wrong one.
     
  16. KentMoney

    KentMoney XS650 Addict

    good luck, let us know how it goes.
     
  17. grizld1

    grizld1 Grumpy old man Top Contributor

    Listen up. A 1* difference is nothing unusual and nothing to worry about; there's usually more grind error than that between lobes. Don't be afraid to alter running valve lash settings slightly to compensate.

    Valve lash for inspection and lift at which valve events are read are set by the manufacturer of the particular camshaft; one setting is neither more nor less accurate than another except for a particular camshaft. Most aftermarket cams are read with 0 lash, Megacycle cams are read at .040" lift, Shell cams at .050" lift. Yamaha XS650 valve timing is specced at .012" lash and 0 lift (very start and very end of valve event). One procedure is neither more nor less accurate than another as long as you set the lash for Yamaha's procedure with a dial indicator to make sure you're not thrown off by a feeler gauge reading the edges of a cupped valve stem.

    In checking valve timing on your rephased motor, the first thing you need to do is to find true TDC on each cylinder and zero your degree wheel accordingly for each one. That will ensure that the camshaft has been correctly welded for the rephase.
     
  18. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Plus, your cam will slowly retard over time as the camchain stretches, as much as 20° in crank degrees, in severely stretched camchains...
     
    Marlin72xs likes this.
  19. Hi 2M, along the lines of cam chain stretch, I hope to yank my engine in a week or 2. I'll measure the cam chain for you. You can use it as a reference. It will have about 65K miles on it. I won't have anything to match it up against since my new crank is will be a 447. I'm curious about how far it was retarded. Hey maybe I'll practice my cam timing on it before I break it down. I could use the practice, since I've never done it before.
    I also may put a 447 sprocket on my 256 cam depending on the shape it's in. No telling what 65k miles has done to it. I'm very religious about changing my oil now, by when I was 26, who knows?
     
    TwoManyXS1Bs likes this.
  20. 5twins

    5twins XS650 Guru Top Contributor

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    Yes, check the cam timing before you remove the chain and cam. Do it with the chain tensioner applied (adjusted). With the rotor mark set at TDC, what you'll be looking for is how far off from vertical the notch in the cam sprocket is.
     
    Marlin72xs and TwoManyXS1Bs like this.

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