Crank vs. Cam vs. Degree wheel numbers... | FerrariChat
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Crank vs. Cam vs. Degree wheel numbers...

Discussion in 'Technical Q&A' started by viphoto, Dec 15, 2010.

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  1. viphoto

    viphoto Formula Junior

    Sep 11, 2010
    264
    Carlsbad, CA
    Full Name:
    Mark
    #1 viphoto, Dec 15, 2010
    I know you guys keep saying keep it simple and this should be...but now I am dizzy and I am not sure if its the brake cleaner I am cleaning the parts with...or from searching the archives for a definitive non cryptic answer..this may be a dumb question and I really do have more mechanical ability than is coming across in my confused posts...last project was British so maybe that's the problem.

    So if I am reading this thread right http://www.ferrarichat.com/forum/showthread.php?t=306281& and using numbers for say a 79 GTB with a F106AE as per the 10/78 OM which are Intake opens @ 16 and closes @48 and the Exhaust opens @50 and closes @ 14

    THEN when reading the "Summit 11" degree wheel" mounted on the Crank am I using the actual numbers on the wheel for setting/checking the cams ( i.e. 16*, 48* etc) and not doubling the opening and closing numbers provided by the OM????? From Fatbillybobs thread on degreeing I understood that for example for 16* I should be lining up to 32* on the crank mounted degree wheel...This is where it gets confusing...as I keep reading that the OM/WSM figures are crank numbers but nobody corrected what FBB was writing and his cams lined up...I am far too right brained to make sense of this and thus it really has me confused...

    Thanking you in advance one more time for taking the time to answer my rookie questions
     
  2. dino clay

    dino clay Karting

    Oct 31, 2007
    185
    san mateo, cal
    Full Name:
    clay cavanaugh
    #2 dino clay, Dec 15, 2010
    keeping it simple means placing crank at top dead center as per timing marks and lining up the marks on the cam shafts and then: JUST PUT IT BACK TOGETHER.

    If you want to do exact cam degree checking. adjust #1 intake and exhaust valve clearance to 0.50mm (.020"), then rotate engine until when you the adjusting shim JUST can't be spun by hand, read your degree wheel.

    IF YOU DON NOT UNDERSTAND THIS SIMPLE EXPLANATION, GO BACK TO THE "KEEP IT SIMPLE DIRECTION"
     
  3. FasterIsBetter

    FasterIsBetter F1 Veteran

    Jul 22, 2004
    5,855
    NoNJ/Jupiter FL
    Full Name:
    Steve W.
    #3 FasterIsBetter, Dec 15, 2010
    Just to follow up on what Clay said, you DO read the degrees of the crank wheel. When you set the crank to TDC on the intake stroke, the intake valve will already be open (it opens at 16* BEFORE TDC. So at TDC, you won't be able to spin the intake shim on #1.) You then rotate the crank just until you can spin the shim by hand, as he said. You can also do it with a dial indicator and you'll know when the shim stops rising and confirm by spinning it by hand. Read the degrees on the crank wheel. The intake valve should close fully at 48* AFTER TDC according to the number you indicated. Keep rotating through the exhaust cycle and watch the lobe on the intake cam. When the lobe makes contact with the shim (you can't turn it by hand), then read the degrees on the crank wheel. It should be 16* BTDC.

    Then repeat the same process with the exhaust cam and see what numbers you come up with.

    Note: We are talking about the intake and exhaust on the REAR bank here. #1 cylinder is the one on the rear bank, closest to the cam belts. On the front bank, #5 is at the other end, and the crank degree numbers will be different so check the manual for those.
     
  4. FasterIsBetter

    FasterIsBetter F1 Veteran

    Jul 22, 2004
    5,855
    NoNJ/Jupiter FL
    Full Name:
    Steve W.
    #4 FasterIsBetter, Dec 15, 2010
    p.s. Make sure you are turning the crank in the right direction when you do this, and don't reverse it.
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,826
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #5 Steve Magnusson, Dec 15, 2010
    Last edited: Dec 15, 2010
    If you mean a Summit degree wheel like this mounted to the crankshaft, then the numbers are read directly, but sometimes you use the outer scale numbers and sometimes you read the inner scale numbers -- hopefully this diagram will help explain:
    Image Unavailable, Please Login

    Where is this FBB thread you are referencing?
     
  6. viphoto

    viphoto Formula Junior

    Sep 11, 2010
    264
    Carlsbad, CA
    Full Name:
    Mark
    #6 viphoto, Dec 15, 2010
    FANTASTIC!.....Thats exactly what I was looking for!...Thank you Steve and yes that is the same degree wheel
    Now the numbers I got, when checking make more sense given how close my assembly/index marks were ( which is what had me puzzled from my earlier thread about possibly jumping some teeth)

    The whole thread by FBB I mentioned is here http://www.ferrarichat.com/forum/showthread.php?t=148917
    post #18 is below which is the one that threw me off.
    That is why I was asking this question, Just wondering why nobody corrected FBB in the above post, (it is a great thread though) and even some of the regulars posted on the same thread which led me to believe that was the way to do it ....that was until I saw the recent threads on the crank vs cam degree call out in the WSMs? I am really hoping I would have figured this out once I actually started the process and got further weird numbers....D'oh! (in a Homer Simpson voice)

    Thanks again to those that took time out of their day to help clear this up for me.
     
  7. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,826
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #7 Steve Magnusson, Dec 15, 2010
    Last edited: Dec 15, 2010
    Glad to lend a hand, and glad that you weren't really 24 deg off, yet had a good-running engine -- because we'd have to burn you as a witch! ;)

    Actually, things went wrong in post #12 in that thread when FBB read the outer scale rather than the inner scale for the intake closing event. He should've said he was measuring 28* (BTDC) and 74* (ABDC) while the F specs were 14* (BTDC) and 53* (ABDC) -- and this makes perfect sense (for a properly adjusted engine), because he was using the operating clearance in making his event measurements; whereas, the F spec is based on the 0.5 mm clearance. Using the (lesser) operating clearance causes the intake opening event to occur earlier and the intake closing event to occur later. It was just a weird fluke that he got "numbers" that he thought were exactly 2X the F spec numbers (and, therefore, wrongly concluded that the F spec must be camshaft degrees).
     

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