SM Ign Timing
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Thread: SM Ign Timing

  1. #1
    Fellow Frogger!
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    Default SM Ign Timing

    I have done a lot of work on Ds but not on SMs hence my query .A friend of mine has an Auto SM and is having trouble getting the timing right, Is it possible to fit the flywheel incorrectly thus putting the timing marks in the wrong place.(Yes, it has been dismantled recently)
    Woody

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  2. #2
    Fellow Frogger!
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    Brian, I'm not sure whether the SM is similar to the D, but I have exactly that issue with my DS23 with Borg Warner auto. The transmission was apparently removed prior to my ownership and installed incorrectly, as the "6mm rod inserted in the hole in the bellhousing" (just below the water pump - see photo; sorry about the size of the image) technique for locating TDC on cylinder No. 1 isn't correct on my car.

    I have (laboriously) used the following method to locate TDC
    • remove all spark plugs
    • place a plastic rod in cylinder No. 1 (resting on the piston)
    • get the motor in roughly the correct position 'bumping' with the starter motor (ignition disconnected)
    • mount a dial gauge above the rocker cover and turn the motor by levering on the ring gear from underneath the car and so determine TDC
      • RL Bachelor shows how to do this on the SM https://www.youtube.com/watch?v=362luW_vX5Y using the starter motor; he also mentions a "flywheel hook" (3 min 36 secs in video) for fine tuning the position of the SM motor.

    I have a vested interest in this, as I'm interested in making a tool to easily turn over the engine of my D to be absolutely certain I have correctly identified TDC on No. 1 cylinder on my car.

    Latest thought: mount a starter motor pinion (which I don't have) on a frame such that it engages with the ring gear underneath the car and turn the pinion with a socket ratchet handle. I also have an old 24 volt sliding gate actuator which turns slowly and if set up with the D pinion could also work.

    I hope you have success with the SM motor and if you have any thoughts on the slow engine turning device I'd welcome them. Chris
    Attached Thumbnails Attached Thumbnails SM Ign Timing-ds23-bw-static-timing-2.jpg  
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  3. #3
    1000+ Posts Ken W's Avatar
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    Hi Brian,

    Below is a section of a page from the SM Parts book that shows the flywheel and a dowel (14) that fits into one of the inner holes. I suppose if the dowel was missing it could be put on in the wrong place. You will have to do some poking down the No 1 spark plug hole to check how the flywheel is positioned.

    My flywheel has an advance marking scale for the A bank (the one that has No 1 cylinder - RHS side of car) but also has a TDC mark for No6 cylinder.

    Let me know if you want more pics of the actual marks.

    Cheers, Ken
    Attached Thumbnails Attached Thumbnails SM Ign Timing-flywheel.jpg  
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  4. #4
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    On SM Auto, the flex plate can only be assembled one way, BUT it is possible to assemble the torque converter 180 degrees out of phase with flex plate. Since the timing marks are on the torque converter, that means the PMH markings are now 180 degrees out.
    Greg likes this.
    Cheers,
    John T.

    61DS19 LHM BVH (son's); 67DS21 BVH; 71DS21 BVH; 73SM 3.0; 73SM EFI (Megasquirt); 73SM 3.0 (other son's)

  5. #5
    1000+ Posts Ken W's Avatar
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    The other difference with this distributor is that the Plug leads will have to be placed in strict firing order not the way they are placed on the twin points standard SM dizzy cap where there is quite an offset built into the rotor between Bank A and Bank B HT switching.

    Getting how the SM ignition system works is quite a brain teaser.

    Cheers, Ken
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  6. #6
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    We will check next week to see if the flywheel is 180 deg out.
    Chris, let me know if you want a starter pinion.
    Woody

  7. #7
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    citquery, investigate the manual. At some point the rod in the flywheel changed from TDC to be about 10deg BTDC if I recall have change correctly. This could have caught you out. Finding TDC via a rod down the plug hole is a tried and tested method. A dial gauge can help as it gives a visual indication of when the travel is at maximum.

  8. #8
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    Quote Originally Posted by Ken W View Post
    The other difference with this distributor is that the Plug leads will have to be placed in strict firing order not the way they are placed on the twin points standard SM dizzy cap where there is quite an offset built into the rotor between Bank A and Bank B HT switching.

    Getting how the SM ignition system works is quite a brain teaser.

    Cheers, Ken

    Firing order on the SM is pretty typical for a V6. It simply fires right then left, front to back (from the driver's perspective). The SEV dual point distributor, on the other hand, is quite confusing.

    I take it this car has been converted to a single coil system. What sort of distributor is installed on this car?
    Cheers,
    John T.

    61DS19 LHM BVH (son's); 67DS21 BVH; 71DS21 BVH; 73SM 3.0; 73SM EFI (Megasquirt); 73SM 3.0 (other son's)

  9. #9
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    Quote Originally Posted by David S View Post
    citquery, investigate the manual. At some point the rod in the flywheel changed from TDC to be about 10deg BTDC if I recall have change correctly. This could have caught you out. Finding TDC via a rod down the plug hole is a tried and tested method. A dial gauge can help as it gives a visual indication of when the travel is at maximum.
    Thank you for your reply, David. Main issue is that my car is a DS23 Borg Warner automatic and unless reassembly is done carefully (as per page 96 of the composite pdf version of the 814 - part 2 manual I have), the rod in the flex plate method doesn't give the correct alignment with the relevant TDC/BTDC position. I agree that done carefully, the dial gauge method should enable a reasonably accurate No. 1 TDC position to be identified and marked on the cam pulley.

  10. #10
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    John, the car has a Stinger Magna Pulse Ign system. Its a pity that the terminals on the Dissy cap are not unevenly spaced.
    Woody

  11. #11
    1000+ Posts Ken W's Avatar
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    Brian,

    Here is my totally theoretical approach.

    It looks to me like the rotor turns anticlockwise in the SM dizzy. So I think the dizzy HT leads need to plug in 1 6 2 5 3 4 in an anti-clockwise direction with a 45 degree separation on the trigger plate between 1 and 6 and a 75 degree separation between 6 and 2.

    Get the engine to TDC on cylinder 1 on the firing stroke (both cam lobes pointing away from the valve buckets). Set the dizzy so that the trigger point is on the sensor and there is a short gap to the next trigger point in the anticlockwise direction. The HT terminal that the rotor points to is cylinder 1 and 6 is the one next in the anti-clockwise direction and so on.

    If you get the timing close enough, the engine should run and then you should be able to give the dizzy some small advance so it runs better.

    Cheers, Ken

  12. #12
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    Quote Originally Posted by brian woodcock View Post
    John, the car has a Stinger Magna Pulse Ign system. Its a pity that the terminals on the Dissy cap are not unevenly spaced.
    Woody
    Odd-fire distributors with evenly-spaced terminals have been around for a long time and work perfectly well. In fact evenly-spaced terminals reduce the frequency of carbon tracks rendering the cap unserviceable. The 45/75 timing must, of course, be built into the triggering mechanism. As long as the rotor tip is wide enough (i.e. 15 degrees at the tip) the spark will always follow the path of least resistance, which means it will still jump to the correct terminal. The GM rotor used in my ignition system is "L" shaped and operates with an evenly-spaced cap. The spark simply fires from the heel of the L at #1, then from the toe at #6, then from the heel at #2 etc.

    SM Ign Timing-img_0137reduced.jpg

    Depending on what type of pickup the Stinger uses, you should be able to figure out which of the three terminals have a 45 degree lead in rotation (#6,5,4) and which have a 75 degree lead-in rotation (1,2,3). As long as you have #1 at one of the terminals that has a 75 degree lead-in rotation, you can assemble the rest in firing-order sequence counterclockwise around the cap.
    cjl likes this.
    Cheers,
    John T.

    61DS19 LHM BVH (son's); 67DS21 BVH; 71DS21 BVH; 73SM 3.0; 73SM EFI (Megasquirt); 73SM 3.0 (other son's)

  13. #13
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    Thanks everyone the car is now running OK. I had to partially dismantle the Dissy to observe the magnetic poles on the Stinger item and obtain the correct alignment.
    Woody
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  14. #14
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    If you have time and the inclination, make some sort of mark at #1 to help out the next owner or mechanic. A simple file mark in the lip where the cap mounts is usually enough.
    JohnW likes this.
    Cheers,
    John T.

    61DS19 LHM BVH (son's); 67DS21 BVH; 71DS21 BVH; 73SM 3.0; 73SM EFI (Megasquirt); 73SM 3.0 (other son's)

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