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Timing

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 1979Jimmy, Jan 29, 2002.

  1. 1979Jimmy

    1979Jimmy 1/2 ton status

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    Im just a crazy amateur mechanic and I was wondering if anyone could give me any help on how to adjust the timing. Picutres would be very helpful.

    79 Jimmy, 5" lift 35 M/T with a 383 puttin out 400hp and 450lb/ft. 4.11s Locked front and back.
     
  2. txbartman

    txbartman 1/2 ton status

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    I don't have any pics, but here you go...

    There are three things primarily for adjusting timing:
    (1) the timing "tab" on the front of your engine and the associated timing mark on the balancer
    (2) the distributor and its "hold-down" clamp
    (3) the vaccuum advance on the distributor

    For tools you will need some sort of engine analyzer or other tool that will help you monitor the engine's RPM. Second you will need a timing light. Finally you will need a special 9/16" wrench for the distributor clamp and a small screw or golf tee for plugging the vaccuum line.

    Here's what you do...
    First, find the timing tab on the front of your engine by the balancer and the associated timing groove on the balancer. I usually mark the groove with soem white chalk or paint to make sure it will show up better with the light.
    Second, disconnect your vaccuum advance line from your distributor. It should be the only vaccuum tube going to it. Once disconnected, be sure to plug the vaccuum line with a small screw or a golf tee.
    Third, locate the distributor clamp and bolt. If you are over the engine and looking down on the distributor, it should be on the manifold at the base of the distributor at about 7 or 8 o'clock.
    Now I would go ahead and loosen it to make sure you can. You only need to loosen it a little, then tighten it back again. That way you know you can get it loose when the engine is running. Be very careful not to twist the distributor when loosening it.

    If your vehicle still has the emissions tag on the radiator support, it should tell you what the timing shuld be and at what RPM. Mine, for example, was 4 degrees at 550 RPM. Now hook-up your engine analyzer and timing gun (usually to the positive and ground connections and a "pickup" on plug #1). If you are hooking up to plug #1, it is the plug closest to the front of the vehicle on the driver's side.

    Now fire the engine and adjust the idle (with the idle screw) until the RPM is as close as possible to the target RPM (in my example, 550 RPM). Now the timing light should be flashing like a strobe. Point it at the timing tab. As it flashes, you should see the timing groove on the balancer light up with each flash. The timing tab is labelled with different degrees on it. There should be a mark for 0 as well as some marks for AFTER and BEFORE. 0 indicates TDC on the compression strokle for piston #1. You want your spark plug to fire before TDC (BTDC). In my case, it should be firing at 4 degrees BTDC. With the tab and the flashing timing light, determine where yours is firing.

    Now, if it is firing somewhere other than where you want it, you will need to adjust the distributor. To do so, you will loosen the clamp again (very slightly) and you will twist the distributor (with the engine running). Very little movement of the distributor makes a big difference in timing. If you think of a circle as 360 degrees, 1 degree is very little movement. Keep that in mind.

    Your distributor rotates clockwise (if looking down at it from the front). If you timing is behind (retarded) meaning your timing light shows it say at 0 degrees or some time AFTER TDC, you will need to rotate the distributor counter clockwise to get the spark to fire sooner. Rotate the distributor VERY LITTLE and then check the timing with the light again. If you are too far advanced (say 8 degrees BTDC), your spark is firing too soon. You will need to rotate your distributor clockwise to get it to fire later. Again, move it VERY LITTLE and check it again.

    Once you get it where you want it, tighten the distributor back down, reconnect the vaccuum advance, and you are finished.

    Hope this helps. More questions, feel free to ask.

    Brian
    Check out <a target="_blank" href=http://tx85gmcguy.alloffroad.com>My Jimmy</a> with all her projects!
     
  3. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    NIcely written, Brian!!!![​IMG]

    Maybe Steve should throw this one into the Tech section. For a lot of us, checking and setting timing is pretty simple, but I'm sure there's a lot of guys out there that could benefit from having this handy when it comes time to do a tune-up.

    Keep up the good work[​IMG]!!!!



    <font color=red>DIGGING AND DIGGING AND DIGGING</font color=red>
     
  4. txbartman

    txbartman 1/2 ton status

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    Thanks. Maybe I could get some pics and do a cleaner write-up. That was off the top of my head. Never hurts to start with the basics. What may be elementary to one person may be rocket science to another. We all had to learn somehow, somewhere! I remember the only problem I used to have with setting timing was getting that friggin' clamp bolt loose and over adjusting the distributor!

    Brian
    Check out <a target="_blank" href=http://tx85gmcguy.alloffroad.com>My Jimmy</a> with all her projects!
     

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