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Check Timing with degree wheel

Discussion in 'Boxers/TR/M' started by Nick G48, Mar 11, 2021.

  1. Nick G48

    Nick G48 Rookie

    Aug 18, 2016
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    Clinton Township, Michigan 48316
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    My car is a 86 TR. We will be replacing a timing belt. The first steps that I intended to do to check the timing with the degree wheel and accuracy of flywheel. Before we remove anything or replace any parts, do valve timing, etc, we decided to do the following. These are the steps. See question at end:
    • Rotate flywheel to PM 1/6, set flywheel to TDC. See photo Image Unavailable, Please Login
    • Set degree wheel with pointer at TDC. See photo (this is TDC at power stroke) Image Unavailable, Please Login
    • Crank 180 degrees. Now at exhaust Continue rotation, stop at 16 degrees before TDC. This is where intake should begin to open: AA/16 degrees. See photo. Image Unavailable, Please Login We are one tooth off (pointer to flywheel). This is equal to 3 degrees on flywheel. Pointer to flywheel should be dead on
    • Am I correct in my steps? Have I missed something? Why the discrepancy?
     
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  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #2 Steve Magnusson, Mar 11, 2021
    Last edited: Mar 11, 2021
    Yes, AA/16 deg BTDC is for a euro F113A TR engine. The US F113A040 TR engine is AA/13 deg BTDC. Use the cam timing values in your 1986 US TR OM, not the cam timing values in the TR WSM. Here's a copy of a "revised" page B48 with a redrawn Fig 52 showing both the euro and US values, and the rotation reversed to how it is more naturally viewed at the crank snout end:
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  4. Nick G48

    Nick G48 Rookie

    Aug 18, 2016
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    Steve, Thank you so much. This was making me crazy. I could not understand what was going on. I appreciate your help and explanation.
     
  5. turbo-joe

    turbo-joe F1 Veteran

    Apr 6, 2008
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    you may check the timing with check-valve clearance 0,5 mm, not with the normal valve play
     
  6. Nick G48

    Nick G48 Rookie

    Aug 18, 2016
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    Clinton Township, Michigan 48316
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    I created a short video showing the use of feeler gages to check valve timing. I was having problems with accuracy until I bent the feeler gage. I think I am getting a good reading now. Thought I would share. Check out the YouTube video below. Anyone do this differently? Looking for input.
    (1) Testarossa valve timing feeler gage - YouTube
     
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  8. Nick G48

    Nick G48 Rookie

    Aug 18, 2016
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    Thanks to everyone for all of the information. As I work through this, I will continue to post findings or questions on this same thread.
    I am still actually just checking timing before I remove and replace timing belts.

    Question:

    Cylinder 7 exhaust opens 44 degrees before bottom dead center and closes 15 degrees after top dead center. Should be open 54 degrees before bottom Center and close 10 degrees after top dead center. If I am off 10 degrees opening, why off 5 degrees only on the close. Why not equal? It does not make sense to me. Any ideas?
     
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    In your audio, I believe you incorrectly state that the valve clearance has been set "at 50 millimeters" -- it should be stated as "point five millimeter" or "point five zero millimeter" (i.e., 0.5mm). Additionally, when describing the measuring shims that you are using, might be better to call them "point four eight" (being millimeters), "point five zero", and "point five three" rather than "forty-eight", "fifty", and "fifty-three" -- JMO (but I have a lot of experience conversing in English with German and Japanese Engineers about metric dimensions, and they would never describe the distance of 0.48 mm as "forty-eight").
     
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  10. vincenzo

    vincenzo F1 Rookie

    Nov 2, 2003
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    Dig thru the above link. Focus on this particular post. Therein lies your answer.


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  12. vincenzo

    vincenzo F1 Rookie

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    I also find it helpful to always cite the zero when speaking of a fractional number:

    Example: aught point five seven mm

    Same line of thought.
     
  13. Veedub00

    Veedub00 F1 Rookie
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    thanks Vincenzo. It looks like using your method, he is off 7.5 degrees on both?
     
  14. Veedub00

    Veedub00 F1 Rookie
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    subtract half of 5 degrees from both. 5 degrees is the difference between 244 degrees and the measured 239 degrees.
     
  15. vincenzo

    vincenzo F1 Rookie

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    OEM duration should be 54+180+10=244deg
    Actual duration measured at 44+180+15=239deg
    Delta = 5 degrees less duration

    this infers that his actual clearance is more than 0.5 mm

    with the existing clearance, he should see
    opening at 54-(5/2)= 51.5 degrees bbdc
    actual is 44... late by 7.5 deg

    Closing at 10-(5/2)= 7.5 deg atdc
    Actual is 15... late by 7.5 deg

    both opening and closing occur at the same 7.5 deg late...
    it appears that his measurement technique is ok. The cam is 7.5 degree late.

    I would have expected more duration than 244 degrees (not 239) since his gap has not yet (?) been opened up to 0.5mm.... a bit puzzling. What is the actual clearance at his measured 239deg duration?

    Long answer to say... “yes, 7.5deg late”
     
  16. Nick G48

    Nick G48 Rookie

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    #14 Nick G48, Apr 14, 2021
    Last edited: Apr 14, 2021
    Are you asking if valve clearance at .50 mm? Shims are changed for valve clearance at .50 mm. Also, why do you divide 5 by 2?
     
  17. vincenzo

    vincenzo F1 Rookie

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    Had you already changed the shim to 0.5mm when you measured the duration of 239 degrees?

    It is unclear to me if you were doing a ‘baseline’ with the running clearance, or if you had already changed to 0.5mm.

    The cams are symmetric... therefore, if the duration is 239 degrees (as you measured) then half of its overall delta (5) affects the opening and half affects the closing.

    If your duration is less than spec 244, it means the clearance is greater than the 0.5mm. With greater clearance, the cam strikes the shim further up its profile.... more rotation is required since the cam profile is more narrow. The 0.5mm is quoted by Ferrari because it gives a clear indication of first contact. At that point on the cam profile, the rate of vertical change per rotational degree is quite large. If you check it at running clearance the ‘ramp up’ rate is relatively low and harder to consistently detect. Aim for 0.5mm - as close as you can get it, but recognize that it will not be exact. A very small change in clearance will make a surprisingly big change in duration.
     
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  18. turbo-joe

    turbo-joe F1 Veteran

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    #16 turbo-joe, Apr 14, 2021
    Last edited: Apr 14, 2021
    I not have my writings here in thailand with me, but when I remember right 0,02 mm is about 3 ° crankshaft to one side, but you have to double, so all then is 6 °, but not sure if I remember right. sorry :(

    becasue the camshafts are symmetrical it does not matter with what valve ceck clearance you adjust the timing. you have to meassure 54° and 10°. when you meassure for example 58 ° and 14 ° then you know your timing is right, only the valve clearance is not exactly 0,50 mm
    when you meassure 58° and 6° then you know the valve clearance is excatly 0,50 mm, but the timing is not correct. have to change those 4 °
    important is nevertheless what valve clearance you have that the opening and closing ° have always the same difference to the 54° and 10°. sure 1° plus/minus is also ok
     
  19. Veedub00

    Veedub00 F1 Rookie
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    the 5 is the 5 degree difference from your measurement to the book measurement. 244-239. The lobe is symmetric, so you need to adjust half of that for each side.if you look at his sketch, you are actually measuring from a higher point on the lobe because it appears your clearance is more than .5 mm.
     
  20. Nick G48

    Nick G48 Rookie

    Aug 18, 2016
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    We currently have.50mm valve clearance at duration of 239 degrees. If I understand you correctly, since my duration is not 244 but is 239, the gap is not set correctly. Cam duration should be 244 with a .50 mm shim. If timing is off, stop and start changes but duration should remain constant. Is my understanding correct?

    I also want to remind everyone that my car has not been started. I do not know why the car was taken out of commission. I have never heard the car run. I am only doing a test and establishing a data point before I change the timing belt.
     
  21. vincenzo

    vincenzo F1 Rookie

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    The only way you can get 239 deg duration is to have a clearance greater than 0.5mm.... or a non OEM cam.

    The duration changes significantly with any change in clearance. Check it yourself.... slip in your next thicker shim to reduce the clearance and recheck your duration. It should significantly increase.

    “If timing is off, stop and start changes but duration should remain constant. Is my understanding correct?”
    Yes... but duration will not necessarily be 244 if your clearance is not 0.5mm.

    Also.... if clearance is off, duration is off and start/stop is off. Count on it. You will likely never achieve exactly 0.5mm nor 244 deg.

    It takes some brain teaser thought to wrap your head around it. Keep looking at the diagrams and the sketch... experiment a bit with shim thickness to confirm you understanding and get a feel how things change with clearance.
     
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  22. turbo-joe

    turbo-joe F1 Veteran

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    yes, when the valve clearance is exactly 0,50 mm

    and as vicenzo has written: the greater the clearance the less duration the cam has
     
  23. Nick G48

    Nick G48 Rookie

    Aug 18, 2016
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    Here is what we did today based on what we understood:
    On cylinder number 7 exhaust we increased shim by .05 mm: 3.85 mm to 3.90 mm
    Exhaust measurements:
    Opens before BDC 45 degrees
    Closes after TDC 17 degrees
    54 + 180 + 10 = 244 degrees
    45 + 180 + 17 = 242 degrees
    Delta = 2 degrees less duration

    Opening at 54- (2/2) = 53 degrees BBDC
    Actual is 45 = 8 degrees late

    Closing at 10 - (2/2) = 9 degrees ATDC
    actual is 17 degrees = 8 degrees late

    We then increased shim by .05 mm to 3.95 mm.

    Opens before BDC 47 degrees
    Closes after TDC 19 degrees
    54 + 180 + 10 = 244 degrees
    47 + 180 + 19 = 246 degrees
    Delta = 2 degrees

    If I am measuring correctly then cylinder 7 exhaust cam is 8 degrees out.
    We believe (not sure) that belts have been changed on the car. During assembly a tooth was jumped. This is what put the car out of commission or running poorly.
    Side note: Cam timing on all other cams measure within reason (within 1 to 2 degrees).
     
  24. vincenzo

    vincenzo F1 Rookie

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  25. Ferrari Tech

    Ferrari Tech Formula Junior

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    Just to be clear, if the spec calls for reading at 0.50mm, you set the clearance at 0.50mm and rotate until it starts to move?

    I always set clearance to zero and set cam timing at 0.50mm of valve movement. I believe the zero to 0.50mm movement is just more accurate.
     
  26. Veedub00

    Veedub00 F1 Rookie
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    If you're 8 degrees out, then it definitely looks like it jumped a tooth. That story makes sense.
    That side had the cat with the partially melted honeycomb too. I read on here that that cam sticks sometimes because of the vacuum pump inducing drag at start up in certain environmental conditions. Don't know if it's true, but makes sense.
     
  27. vincenzo

    vincenzo F1 Rookie

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    #25 vincenzo, Apr 16, 2021
    Last edited: Apr 16, 2021
    1) more or less... yes. with the method I put forward.... you get close to 0.5mm clearance in order to measure at a point on the cam profile where the ramp up rate of change is relatively high (lots of valve movement with little cam rotation). Easy to see, more precise. Factory cited as a methodology. Then calc the needed opening point based on actual measured duration. This eliminates the small and inevitable inaccuracies in clearance.

    2) how do you set clearance at zero? Shim selection sizes force you to have a gap... or compress the valve. No such thing as a ‘perfect’ shim unless you measure and then surface grind a shim to suit. Incredibly difficult to get it spot on. Theoretically, your method sounds like it would work... but in practical terms, achieving zero clearance sounds problematic. It would be interesting to try the various methods and compare the results.

    Keep in mind, at the very base of the cam, the ramp-up rate is intentionally very low to minimize cam loading. Harder to detect and get repeatable measurements. With little clearance, while reading the gauge.... you first get a ‘jiggle’, then a bigger jiggle but still no real movement, then an ever so slight, perceptible movement in the needle. With more clearance, you get nothing.... nothing... then BAM, the needle moves. What I am trying to describe is how the oil film affects your gauge reading at low ramp-up rates. Very difficult to perceive ‘opening’ from ‘jiggle’. Doing this on closing, rather than opening is even more difficult. You can set the cams by ignoring the closing, but you have no confirmation that you got it right. Errors go undetected.

    Excuse the unscientific terminology.... best I can do.
     

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