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Thread: Step-by-step valve adjustment instructions

  1. #1

    Step-by-step valve adjustment instructions

    This was a great reply by Ed Mayo on the PCA.org Technical Q&A Section. Note to Ed and/or moderator, please let me know if it should be deleted due to any copyright issues (I did not see any on the E-mail I received)...

    Classification: Engine
    Subject: step by step valve adjustment instructions
    Model: 911T
    Year: 1973
    Total Mileage: 86000
    Car Use: General

    Question:
    I would like to attempt a valve adjustment during my next oil change do you have any good step by step instructions ? The manual that I have (Haynes) is not very clear what takes place after finishing the first cylinder. I have the proper feeler gauge, and gaskets, etc. I would just like a little more info.

    Answer:
    The first answer is that you adjust the valves in the same order as the engine firing order, that is 162435. If you don't already, you need to know the location of the cylinders, that is looking from the rear of the car the rearmost cylinder on the left (drivers side) is #1, going forward is #2 then #3. The right side is 4-5-6, #4 being at the rear. The decals on the engine lid latch panel will show this (if they're still there). This can also be found in the owner's manual, not to mention your Haynes manual. By the time you're done you will have rotated the crankshaft two complete revolutions. You will need to look carefully at the crank pulley so that you can find the marks you'll need that indicate cylinder TDC (top dead center). For as much as you'll be rotating this engine you'll find it easier to remove all the spark plugs first, but it can be done with them in if you wish.

    Rotate the engine either by using the wrench on the fan pulley (you'll need to always push against the right side of the fan belt to get enough tension) or use a long series 19mm box end wrench on the crank pulley nut. You'll need a good light at this point to see the crank pulley marks, turn crank until you get the TDC mark lined up with the notch in the blower housing. There are two marks, one at TDC and one a ¼" away which is 5 degrees after TDC. There are also two marks at 30 and 35 degrees advance which look the same. Be sure you don't have them! You may need to use a light and mirror to see the marks. They are all stamped with appropriate numbers, Z1 is the mark you want, put a dab of white or yellow paint on it.

    Now rotating the crank clockwise the next mark you see (in about an inch) is marked FE, you don't need that, keep going, the next mark will not be labled, and it should be about 120 degrees from the TDC mark, paint mark it.

    Rotate engine 120 degrees more, find mark and paint it.

    Rotate 120 degrees again and you should be back at Z1 (you'll have passed 30 and 35 degrees marks).

    Now remove distributor cap and find small mark indicating #1 cylinder firing position for rotor, rotate engine so that Z1 pulley mark aligns with notch, and rotor TIP is aligned with mark on distributor.

    Now you adjust valves on #1 cylinder.

    Next rotate engine so the next painted mark aligns with blower notch, that will be cylinder #6 (next in firing order).

    Next 120 degrees will be for #2, then back to TDC which will be #4, and so on.

    Now all you have to do is develop that "feel" for the adjustment. You will break several blades until you develop this. You have to "walk" the gauge in between the valve and rocker, and it must be perfectly flat. Most people tend to make the adjustment too loose, .004" means you could not get a .005" blade in there. Good luck.

    Ed Mayo - PCA WebSite - 7/27/2007
    Peter Kane

    '72 911S Targa
    Message Board Co-Moderator - Early 911S Registry #100

  2. #2
    Hi Peter, thanks for the compliment, glad you thought it was worthy. I'm not aware of any copyright infringement once I post an answer to the questioner and subscribers (of which you're one) I think PCA only gets their dander up if someone hacks into the PCA site and then sells the information. If I ever learn anything to the contrary I'll let you know.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  3. #3
    Senior Member 911kiwi's Avatar
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    Auckland, New Zealand. And Los Angeles, USA.
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    alternative valve adjustment method

    Anyone else used the "backside" method of valve adjustment. Been using this for a couple of years now - non-traditional but way easier & faster.

    Check it out on the Pelican Parts tech section. Apologies if this have already been posted recently!
    Kiwi
    1972 911S
    1967 912
    1959 356A Conv D
    Early S Registry # 306

  4. #4
    asking again:

    what's the general opinion on the backside technique?

    http://www.pelicanparts.com/techarti...alveadjust.htm

    thanks
    73 911S Targa

  5. #5

    Step-by-step valve adjustment instructions

    I'm probably not the best person to respond to this since I've been doing the valve adjustment the traditional way since the 911 first came out, and therefore I find it easy and natural. I've seen the back side procedure but have never tried it. I'd suggest you try them both and see which one YOU like. As long as the results are the same it don't matter! Either way the goal is to have a correct "feel" with the feeler gauge. Most people, as I mentioned above, tend to use too 'loose' of a gap. You need to develop a feel for the necessary drag on the feeler blade.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  6. #6
    The backside method is premised on one very important and WRONG (in my humble opinion) assumption-- that the clearance between the cam's base circle and the rocker face is equal to the valve clearance divided by a constant rocker arm ratio.

    Let me back up for those who don't want to click the link.

    Normal valve clearance is 0.1mm. (that is 0.003937" for those in decimal-inch)
    The "rocker ratio" is 1.4 to 1. That means that the adjuster tip end of the valve moves 1.4mm for every 1mm the rocker face moves.

    If you divide 0.1mm by 1.4 you get 0.071mm or 0.002812" This is rounded off to 0.0025 inches, or twenty-five ten-thousands of an inch.

    The backside method calls for measuring the clearance using this thinner feeler gauge between the cam base circle and the rocker face.

    Here's the problem: the rocker ratio isn't constant-- it varies depending on where you measure it. Remember that the rocker face is curved-- so the rocker arm ratio actually changes as the cam wipes across the rocker face. Rocker ratio is defined as the distance between the center of the bore and the adjuster tip divided by the distance between the center of the bore and the contact point where the rocker face touches the cam. Since the latter moves as the cam rotates, the rocker ratio is variable, not fixed.

    In a pushrod V-8, the rocker ratio IS more or less fixed because the pushrod doesn't move back and forth on the rocker arm.

    Now, the geometry pundits will point out that you aren't measuring across the rocker face, you are measuring between two circles that have (theoretically) only one point in comment that is tangent. And it's there that the feeler gauge is placed. To which I say, "prove to me that the 1.4 measurement is taken precisely at the point on the rocker face that is tangent to the cam's base circle when the clearance is set on the OTHER end at 0.1mm, and I'll start using the method!

    But what the hell do I know, I use a dial indicator.
    1966 911 #304065 Irischgruen

  7. #7
    Senior Member karlusmagnus's Avatar
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    John, could you give us a bit more detail?
    Karl: E911SR #792 ; RG #420 ; GS #7

    '72T Coupe - Sepia Brown

  8. #8

    Step-by-step valve adjustment instructions

    Karl, you subtle son-of-a-gun, I about fell out of my chair

    I suppose the only way to decide this (for me anyway) would be to use the back space method , then check clearance the traditional way and see if the feeler gauge drag feels the same as I would have normally set it. Maybe on the next engine build I'll take the time to do a test.

    John, are you gonna slap Karl upside the head?
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  9. #9
    thanks for the input, guys

    I don't do the adjustment very often as I don't put a lot of miles on the car - I may try both methods

    (I also may farm it out to a pro...)
    73 911S Targa

  10. #10
    Ed, I have something better in mind: at our next McSorley's outing, Karl will be required to sit next to ME again. After the fourth or fifth round, all the specifications, statistics and procedures begin to spill forth. . . randomly. . .
    1966 911 #304065 Irischgruen

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