[v12-engine] cam timing again!

My problem is that at TDC the cam lobes on piston A1 are in the
correct position ei both lobes are pointing into the air, notch in
cam is in the 12 o’clock position all seems correct so far . now by
my calculations piston B1 being number severn in the firing order
should be 60 degrees BTDC on its exhaust stroke which is to the
naked eye about where it is ie both lobes of the cam pointing down
but slightly one sided however the notch in the cam is at six
o’clock everyone I have spoken to tells me both notches should be
at 12 any ideas ( the left and right cams are spaced differently so
it can’t be left cams )–
ken37
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In reply to a message from ken37 sent Sun 14 Nov 2004:

I just took my engine apart to do the dropped valve seat
repair. I checked the timing before I disassembled it and
with the crank at top dead center both cams had the notch
straight up. Stop trying to figure out what is happening and
assemble it as jaguar suggests. You will be fine. Nerves
sometimes get the best of us. Good luck!!!–
Greg 1985 XJS HE DANA rear
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Hello Ken,

Let’s review where everything should point in sequence at TDC:

  1. The number one piston on the A bank should physically be at its apex.
    With the cams off the car, and the chain and sprockets hanging from the
    built in hangers, this is best determined by measuring down each spark plug
    hole for pistons 2, 3, 4, & 5. The depth down to all 4 should be precisely
    the same, since piston 1 and 6 are at top dead center when 2 & 5 are midway
    down and 3 & 4 are midway up. When midway coincides with all four center
    pistons, 1 and 6 are at TDC. Also note that A Bank is on your right-hand
    side looking out the windshield when seated in the driver’s seat. Also,
    avoid turning the motor over backwards as it can be destructive to the
    timing chain tensioner. Removing all of the spark plugs will make turning
    the motor over easier. Remember to attach a catch hose and canister to the
    disconnected fuel line.

  2. Once placement of 1A is established as TDC, the solid line next to the
    “A” mark on the crankshaft damper should perfectly align with the 0-degree
    mark on the timing plate bolted to the front of the sandwich plate. The
    crank damper bushing has been known to sheer allowing the pulley to rotate
    irrespective of the rest of the crank. A woodruff key holds the pulley to
    the front of the crank, and it has been reputed that this woodruff key can
    shear, allowing the for the same result. If your “|A” mark is not close to
    the 0-degree mark, one of these scenarios has happened to you, and you’ll
    have to remedy the crank damper situation before the “|A” mark can be relied
    upon for timing the engine.

  3. The timing plate is bolted to the sandwich plate through eliptical bolt
    holes allowing for adjustment of the plate. Once step 1 is assured, and the
    damper is determined to be intact in step 2, unbolt the timing plate and
    align the 0-degree mark with the “|A” mark on the damper. Align the plate
    with the “|” mark, not the point of the “A” mark.

  4. At this point, a dot peened in the face of the jock shaft pulley should
    be at the 6-o’clock position. (You won’t be able to determine this though,
    unless the front cover is off). I can’t image how critical this is, since
    the jock shaft is not lobed.

  5. The distributor body should be mounted such that the vernier adjuster is
    centered at the Zero mark on the scale. This will allow fine tuning in
    either direction when you time the engine. Also, the 3 allen bolts that
    hold the distributor to the center cover should have room to rotate the
    distributor housing both clockwise and counter-clockwise. The flash shield
    should be installed with the raised line pointing towards the left front
    headlamp, and the metal contact end of the rotor should be aligned with that
    raised line on the flash shield. If your flash shield is missing or doesn’t
    have such a raised line, ensure that the contact end of the rotor is
    pointing towards the left front headlight, and especially not towards the
    right hand door. Installing the distributor to the center cover one tooth
    off is very conspicuous, so if you don’t have the mark on your flash shield,
    trace the rotor onto it with a magic marker once you’ve established TDC for
    easier identification later.

  6. Without rotating the motor, BOTH cam shafts should be re-bolted to the
    tappet block with the aligning notch at the 12-o’clock position
    perpendicular to the face of the tappet block (since it’s a vee configured
    engine, each tappet block is canted. A tool is made that ensures that the
    notch is at the 12-o’clock position relative to the face of each tappet
    block (C3993, I believe) and costs about $14 dollars. It is inexpensive
    enough and not readily home-fabricated, so order one from Motorcars Ltd. or
    one of the other suppliers. Start all the bolts and gently tap squarely on
    the face of a camshaft lobe with a hammer to align the notch to 12’o-clock
    as you torque the bolts to spec.

Both lobes above the #1 cylinder on the right-hand (A-Bank) cam will be
pointing up (not compressing either intake or exhaust valve spring) since 1A
will be on its compression stroke.

Ensure that your vehicle has not been re-assembled at some point with two
right-hand cam shafts or two left-hand cam shafts. Ensure that the right
and left cam shafts have not been transposed at some prior point.

  1. Re-engage the sprockets to the cam shafts without allowing the chain to
    slip off any of the 4 sprockets involved (crank, jackshaft, and both cam
    sprockets). Pull the spring clip out of the sprocket and rotate its inner
    splined section until the four bolt holes align with the cam, then reinstall
    the spring clip, ensuring that it is seated into its groove in the sprocket.
    Start with the left hand sprocket, then move over to the right. If you
    have not engaged the timing chain tensioner, it is helpful to have an
    assistant pull up on the timing chain tensioner with a heavy hook tool
    (easily improvised) while you position the right-hand sprocket onto the
    right hand cam shaft. Align the bolt holes on the right-hand sprocket with
    its cam by removing the spring clip and locating the splined center portion
    as performed on the left side if necessary.

  2. If you did engage the timing chain tensioner, disengage it carefully and
    completely when you have completed the above steps. Dynamically time the
    car to 18 degrees BTC (or according to your country’s spec, as labeled on
    the sticker under the bonnet) with the vacuum advance disconnected and the
    engine running at 3000 RPM using a strobe timing light by adjusting the
    vernier adjuster on the distributor. Tighten the adjuster lock nut when
    complete. If more adjustment is required than the vernier adjuster permits,
    you will have to remove the distributor cap, loosen the allen bolts, and
    turn the body of the distributor to provide more room for adjustment.

If something is preventing these steps from being carried out, you must
determine why. The most common reasons are a slipped crankshaft damper, a
distributor installed 180-degrees out, or in your case, possibly the car was
assembled at some prior time in the past using two left cams or two right
cams, and the mechanic inverted one of them to try to achieve satisfactory
results. Else, the left and right cams are reversed?

My problem is that at TDC the cam lobes on piston A1 are in the
correct position ei both lobes are pointing into the air, notch in
cam is in the 12 o’clock position all seems correct so far . now by
my calculations piston B1 being number severn in the firing order
should be 60 degrees BTDC on its exhaust stroke which is to the
naked eye about where it is ie both lobes of the cam pointing down
but slightly one sided however the notch in the cam is at six
o’clock everyone I have spoken to tells me both notches should be
at 12 any ideas ( the left and right cams are spaced differently so
it can’t be left cams )

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !From: “ken37” kendean@aol.com

1 Like

Dear Joseph Taylor.
Thank you for a very good describtion of how to set the timing.
Did i do anything wrong because:
In your article 1. You write that when cylinder 1 and 6 are at top dead center when 2 & 5 are midway down, and 3 & 4 are midway up. In my engine it is opposite 2 & 5 are midway up and 3 & 4 are midway down.
Have I done anything wrong?
Kind regards Joergen from Denmark