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Thread: Top dead center compression stroke Help!

  1. #1
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    Top dead center compression stroke Help!

    A few weeks ago I blew a head gasket in my blazer. Due to lack of funds I have undertaken the job of rebuilding the top half of my vortec v-6. I am nearing the stage of installing the distributor and the shop manual says I need to position the crank so I am at top dead center on the compression stroke of cylinder #1. Are there any mechanics in the family that can tell me how I determine this position? Can somebody help me turn my garage back into a woodshop?
    Victor

    A picture is worth a thousand words.
    A video is worth a thousand pictures.
    Experience is priceless.

  2. #2
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    Quote Originally Posted by Victor Skellett View Post
    A few weeks ago I blew a head gasket in my blazer. Due to lack of funds I have undertaken the job of rebuilding the top half of my vortec v-6. I am nearing the stage of installing the distributor and the shop manual says I need to position the crank so I am at top dead center on the compression stroke of cylinder #1. Are there any mechanics in the family that can tell me how I determine this position? Can somebody help me turn my garage back into a woodshop?
    Sorry Vic I can not help you. It's been to many years sense auto shop class in HS.
    I dream a lot. I do more painting when I'm not painting. It's in the subconscious.
    ::: Andrew Wyeth :::
    colonialrestorationstudio.com

  3. #3
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    TDC

    Look for timing marks on the front end of the crankshaft.

    Should be a mark and a tab for TDC and maybe some timing marks with +- 5/10/15 degrees

  4. #4
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    Pete I remember that now LOL, as I tell my son Jarrod I have forgotten make then You will ever imagine.
    I dream a lot. I do more painting when I'm not painting. It's in the subconscious.
    ::: Andrew Wyeth :::
    colonialrestorationstudio.com

  5. #5
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    I believe with the valve cover off the drivers side, and spark plugs removed, you should see the intake valve close and then feel the piston top out on the stroke for cylinder #1, this should be Top dead center.

    A good place that I use is for vortec advice is: http://www.chevytalk.org/fusionbb/sh...p?fid/78/fp/1/

    The guys on that site are always very helpful.

    Additional info: There are two TDC, compression stroke and exhaust stroke, this is where I mentioned that the intake valve should just be closing and then the piston will be coming up for it's compression stroke. You can also use a straw or dowel and mark it as it comes up to determine where it reached the top at. Just don't use something that will break off in the cylinder.
    Last edited by Darren Wright; 09-27-2010 at 09:56 PM.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  6. #6
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    Darren is right on, with the valve cover off, you can see the pushrods/lifters. On top dead center of compression stroke the piston is compressing the fuel air mixture in the cylinder, at TDC the plug fires igniting the mix pushing the piston down (power stroke now). Next time up is exhaust stroke because the exhaust valve is open and the upward motion of the piston is pushing the burnt fuel/air mixture out. At TDC then the exhaust valve closes and intake valve opens, piston goes down sucking in (kind of like inhaling hence intake) the new fuel/air mixture, at bottom dead center the intake valve closes (exhaust valve is still closed) compression stroke is beginning, at TDC the mixture gets ignited again. Thus you need to identify which cylinder is #1, find both valves for that cylinder and when the piston is at the top of its stroke and both valves are closed, you are at TDC on compression stroke. By the way, that is the four strokes of a four cycle engine! Good luck, can be an intimidating task, but man will it make you feel good when it is done and you saved all that money! Hope this helps.
    Jon

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  7. #7
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    What Pete, Darren and Jonathan said is right on the money

    One more point, take the spark plugs out when you do this, MUCH easier to turn the motor over by hand with them out
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
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  8. #8
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    Quote Originally Posted by Stuart Ablett View Post
    One more point, take the spark plugs out when you do this, MUCH easier to turn the motor over by hand with them out
    Then use a little stick or straw to determine the tdc

    also PLEASE NOTE which is cylinder one, i think they count from the cabin

  9. #9
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    Thanks everybody! With your help I found the correct position last night and in a little while I'll install the distributor. Thanks again!
    Victor

    A picture is worth a thousand words.
    A video is worth a thousand pictures.
    Experience is priceless.

  10. #10
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    I look forward to seeing how all goes for you. I just had the upper intake off of mine to change the fuel regulator, boy what a pain. Had to literally remove the upper wiring harness to get the thing off. Still have my main issue with it cutting out, but it did fix one of the symptoms I was having. I only had 53 lbs of pressure when it was suppose to be 55 - 65, at least it's back in that range.

    Good luck!
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

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