70 z28 won't start after upgrades

Discussion in 'Troubleshooting & Diagnosis' started by mykul48332, Feb 8, 2006.

  1. Cardinal

    Cardinal Veteran Member Lifetime Gold Member

    8,191
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    Jun 22, 2003
    Endicott, NY
    The cam and crank marks have to be in alignment.

    When you get them aligned, the engine can be on either #1 or #6 depending on where it the cam is in the firing order as the crank comes around twice at TDC, once for #1 and once for #6. That's why you have to make sure that you're on #1 in the firing order by holding your thumb over the open spark plug hole for #1 and then aligning the mark on harmonic balancer with the zero mark on the timing tab. The assumtion is that when the harmonic balancer and the timing tab zero are together that the #1 piston is at TDC which is why you have to make sure that these two parts are aligned to TDC.

    It's a chain of events that have to be in sync or nothing works with the crank, pistons, cam, valves etc. If they're our of sync then the valves are open under compression and closed during exhaust or intake.

    If all this confuses you, then you need to seek professonal help before you do irrepairable damage (bending valves, broken pistons, etc.)
     
  2. 74BIBELOT

    74BIBELOT Veteran Member

    hi; check the timing gears, the intermediate gears seems to be the same size, but they are a little bit different. if you install them wrong the timing will be off. try with a timing chain, the marks should be cam 12' o clock crank 12', put a straigh rule between the 2 gears to be sure. you can start the engine (few seconds) without the timing cover. When you put the timing marks crank 12 cam 6 you are in #6 compression. sorry for my english from juarez mexico. victor
     
  3. softail1940

    softail1940 Veteran Member Gold Member

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    Jul 7, 2005
    Connecticut
    Well...... I am waiting for results...:)
     
  4. 468RAT

    468RAT Veteran Member Lifetime Gold Member

    Not to rain on anyones advice but do not start that engine with the timing cover off. There will be nothing to hold the two dog bone connected gears in line with the cam and crank gears of that gear drive. Yes, hopefully they stay there BUT if they don't you will bend and bang since nothing is keeping the timing. I don't think with all you are doing is now the time to cut a corner. With the gear drive and timing installed correctly, button it up and you are done with that part. As far as a double idler gear drive set up, the idler gears have to be the same size for they are running on the same set of gears. If this was not true you would have a ratio difference that would not be compatable with what is trying to be acheived. The idler gears are just that. They provide the connection to the cam and crank gear. The idler gears have nothing to do with timing. As stated, the timing is in the cam and crank gear positioning, the idler gears just provide the final driving connection.
     
  5. 74BIBELOT

    74BIBELOT Veteran Member

    maybe my english is not enough. but when i said start the engine a few seconds with a TIMING CHAIN, not with the GEARS. The idea was to aisle the problem. i can understand english reading, but writing english take me more time. saludos
     
  6. mykul48332

    mykul48332 New Member

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    0
    Feb 8, 2006
    Ok, let me address a few things, then get on with the auto saga

    First, the bone connected gears are two different sizes, the left side (facing from the front) is bigger than the right. These are the Jegs gears, and we have directions for them (kinda)

    next: I don't know a lot about cars, but I've seen one too many horror movies to start the car with the timing cover off. :)

    And on to the car....
    We called a professional mechanic who said this : "with that kind of engine, if it goes out of time, the only way to get it back in is to point the crank key toward #1, that'll be TDC on 1"
    "next you gotta make sure the timing mark on the cam gear is pointing straight down."

    so... we turned the crank until the keyway (not the timing mark) pointed to #1...SUPRISE
     
  7. mykul48332

    mykul48332 New Member

    21
    0
    Feb 8, 2006
    Ok, let me address a few things, then get on with the auto saga

    First, the bone connected gears are two different sizes, the left side (facing from the front) is bigger than the right. These are the Jegs gears, and we have directions for them (kinda)

    next: I don't know a lot about cars, but I've seen one too many horror movies to start the car with the timing cover off. :)

    And on to the car....
    We called a professional mechanic who said this : "with that kind of engine, if it goes out of time, the only way to get it back in is to point the crank KEY toward #1, that'll be TDC on 1"
    "next you gotta make sure the timing mark on the cam gear is pointing straight down."

    so... we turned the crank until the keyway (not the timing mark) pointed to #1...SUPRISE...When we checked it with our piston stop (thanks much for the directions) #1 was TDC!
    then we turned the cam until the timing mark was pointing straight down. We checked the chiltons, and the picture for crank and cam was in the exact same place! We both feel that it is right now, but we won't be able to button it up until thursday, when the boss returns to the US.
    We have gotten so much good advice on this board that we check it all through here first.

    So...a few questions:

    most important, when we take the R valve cover off, to see the rockers over #!, they both seem to be at the same height. (as opposed to one side up(intake?) and one side down (exhaust) they both seem to be at halfway. Is this right, or does one or the other side have to be up?

    next.....I keep hearing that the timing mark comes up at 1 and 6....if we've adjusted to #1 on the crank and moved the cam seperatly, does this matter? (meaning, is there something we have to do to make sure the right valve is opening/shutting?)

    BTW, the crank sprocket has three marks, a circle to match the one on the cam sprocket, a triangle, and a rectangle (which is exactly in line with the cam mark (cam 6/ rectangle 12)) could this be for other models, or is this our way of knowing where #1 is?

    when we moved it the way we have it, the gears slid right in with no troubles, the distributer dropped right in with the rotor pointing at #1, and everything perfect.

    one final (really) question: my boss is concerned with the valves (or are they called rockers? they're right under the valve cover), he says they're tight (can't even be wiggled) but when they were first taken off (back in december) they were 'a little wiggly'....I don't have any idea what he means, but someone out here should.

    thanks again, and it's really nice to find a place where all the input is constructive.
     
  8. SecGenLvr

    SecGenLvr Member

    73
    0
    Feb 8, 2006
    Tucson, AZ
    With the cam, the only way to know where you are at is to look at the valves, if #1 is at TDC then both valves should be closed because it is on the very begining of the power stroke, which means no gas should escape the cylendar, at the same time #6 should have the exhaust port open because it just finished the exhaust stroke... now that is why the timing mark comes up at #1 and #6.
    When the #1 cyl is on compression #6 is on exhaust and vise versa, when the crank spins once the #1 cyl went from compression to exhaust and the #6 went from exhaust to compression, which is why there are two TDC's because it is a four stroke engine...
    So, if you have your #1 in TDC in the compression stroke then the distributor should be on the #1 cylendar, but if you have the TDC where #1 cylendar is on the exhaust stroke your distributor should be on #6 because it will be on it's compression...
    One way to know which it is one is to remove the #1 spark plug and wire, have someone crank the engine with the coil unplugged, and the distributor cap off, put your finger in cyl #1 hole and you will be able to feel the compression stroke and it will try to blow your finger out of the hole...
    watch the distributor and if the rotor passes #1 wire peg every time you fell the cylendar blow, then you have the right timing placement for your distributor, if you don't then something is wrong and post results...
     
  9. Twisted_Metal

    Twisted_Metal Moderator Staff Member Lifetime Gold Member

    25,270
    286
    Feb 26, 2004
    Bloomington, MN
    From your description, You have everything in the right place. Both valves on #1 should be closed at TDC of the compression stroke.

    Sounds like the issue was caused by the cam and crank being out-of-synch. I'm glad you had the valve/piston clearance in this engine to do this without destroying the valve train. (Some engines will let the valves and pistons hit each other if the cam and crank aren't in synch. An expensive mistake!)

    Hope it fires up without further problems on Thursday!
     
  10. SecGenLvr

    SecGenLvr Member

    73
    0
    Feb 8, 2006
    Tucson, AZ
    Yeah if it was an interference engine you would be totally f*^ed, unless it is and then you are...
     

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