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Since when is 30 degrees BTDC timed?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blazer_Boy, Apr 5, 2002.

  1. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Tried to time up the new hot rod motor in my shortbox and the timing mark is way to the passenger's side when I hit it with the light. The block appears to be from the early 70's. It came out of a burnt vehicle and the timing cover and damper were swapped out because the damper was no longer useable. It was bolted to a TH350 and had the melted remains of a Q-Jet on top. It had the old orange paint too. Sorry for all the details, but this all I can remember for dating it. I believe the deck code was TKY.

    The 8" damper and cover I have on it now came from an '85 suburban. I popped off the front pulley and compared the damper to another one and the marks do match, so the outer ring has not slipped. If I bring #1 to TDC by hand (using an old dipstick in the plug hole to get a rough idea), the notch on the damper is around the 30 BTDC range at TDC. What gives?

    I know GM used two style 8" dampers over the years. One has the mark 10 degrees before the keyway and the other 2 degrees. The new mark I made with my TDC is about an inch towards the driver's side. Now 8 degrees off is only like a half inch, double that and I may be in the ball park. Is the fact that damper goes around twice in a complete cycle have anything to do with getting to that magic 16 degree one inch adjustment. If I do the match and figure out the circumfrance, divide 360 degrees and multiply that by 8 I end up with .558". I'm about double of that number off.

    I'd prefer finding where to put a new mark, because its a pain to replace it when the motor is installed. Does anyone have both style dampers and could measure the diff for me.

    Thanks
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    There were two different timing covers too. One had the pointer on the passenger side and the other had it on the drivers side. I have no idea what years had which cover...

    Rene
     
  3. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    I noticed that too when I pulled the tarp of my '82 (don't ask about the never ending body project) and saw that different style. Looks like all target motors have that, along with the old stlye temp senders. I was wondering if maybe I have some goofy model where it has the 2 degree before key way and the timing cover with the markers in the center. Usually the center style ones use the 10 degree before the keyway damper. Really ticks me off because I took it for a test run and it was hot stuff. The timing was just a micron off when I tried to start it warm. I couldn't shift the damn gears fast enough when I pulled out of the gate and onto the higway /forums/images/icons/cool.gif. Nothing like my '82 K5 with 3.08s and 31"s....putt putt putt.
     
  4. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I would probably buy the timing tape...

    To get exact TDC pull the plug out of number one and insert some sort of stop like a 1/4" socket extension through the spark plug hole, rotate until the piston hit's your stop and make a mark on the balancer and the cover. Now rotate the other way until it hits the 'stop' again. mark it there too. TDC is exactly in the middle of your two marks. Once you have TDC accurately established apply the timing tape.

    Rene
     

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