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  1. #1
    thompsdw's Avatar
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    Diagnose this Failure??? Wow!!!

    Ok, this is more of a failure diagnosis thread so here are some facts upon disassembly of my 2002 GTX 4-Tec NA. It had just over 100 hours on failure. Here are some facts:

    1) Head was dirty, but otherwise functional. None of the valves appear to be bent.

    2) Timing chain was broken, stretched link.

    3) Chain tensioner cylinder missing. Latter found in bottom of mag cover shattered in pieces.

    4) Starter drive gear shaft failed. Several gears on the bendix portion of the starter gear were stripped. It was still in position upon disassembly (no parts in bottom of mag cover).

    5) Ring gear teeth have a little wear, but nothing that is really drastic. Note heat mark on the ring gear near the flash reflection. Chain dragging on ring gear?

    6) Not sure what spring or metallic tip is by the shattered tensioner cylinder (far left photo).

    7) There is a lip on the lower case half below the lower timing chain gear that had some damage after the chain failed. Good news I guess because it really doesn't appear to serve a purpose. I was worried about the cases, but they stood the blow of this failure.

    The crank freely rotates and the cylinders are so clean I can see the factory hatch marks.

    The previous owner (I purchased it failed) thought the starter was bad and replaced it . Crankshaft was turning all the time so I don't know what they were thinking, but I am sure they were cranking on it to get it to start. Could the drive gear be a secondary failure??

    What the hell happened here?
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    Last edited by thompsdw; 01-23-2008 at 09:43 PM.


  2. #2
    thompsdw's Avatar
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    No ideas on how this could have occurred?? I was thinking it might add some insight as to how the random chain failures occur if we could determine the mode of failure on a NA engine (no ceramics to get in the chain). Ideas????

  3. #3
    BIG BOOST stickem's Avatar
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    looks like the timing chain let loose and busted everything else up whats the cam gear look like and fly wheel? I still would break that motor down and clean it out.
    Last edited by stickem; 01-24-2008 at 07:55 AM.

  4. #4

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    im no expert but to me it sounds like something bound up and caused a lot of stress and pressure on the chain and shaft.

    was there any liquid in the cylinders? possibly the engine hydro locked?

  5. #5
    Quote Originally Posted by stingray152003 View Post
    im no expert but to me it sounds like something bound up and caused a lot of stress and pressure on the chain and shaft.

    was there any liquid in the cylinders? possibly the engine hydro locked?
    Hydro lock would bend a rod not break the chain been there before.

    I think the starter gear may have broke a tooth or 2 off and it dropped in the timming chain and that is what broke that.The rest of the damage was from the chain breaking.Then the motor stoped no more damage after that.The oil pumps might be OK if you clean it out.I would tear it apart and clean it for sure.

  6. #6
    thompsdw's Avatar
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    Quote Originally Posted by stickem View Post
    looks like the timing chain let loose and busted everything else up whats the cam gear look like and fly wheel? I still would break that motor down and clean it out.
    They are fine. Minor engagement wear on the ring gear, but it looks like normal drive gear mesh.

  7. #7
    thompsdw's Avatar
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    Quote Originally Posted by mitch411RXP View Post
    Hydro lock would bend a rod not break the chain been there before.

    I think the starter gear may have broke a tooth or 2 off and it dropped in the timming chain and that is what broke that.The rest of the damage was from the chain breaking.Then the motor stoped no more damage after that.The oil pumps might be OK if you clean it out.I would tear it apart and clean it for sure.
    That makes sense to me, but I have a great deal of difficulty seeing the chain causing the drive gear shaft to fracture. I am still amazed that the valves are OK. If it were a ceramic disk or drive teeth - I think the chains fail due to something getting in them. The chain tensioner the only thing that throws a kink in this thinking to me. I don't see how it could of disentigrated the way it did ...........

    BTW - no signs of hydrolock anywhere. The crank turns freely. I still will open the cases to clean out tramp metal from the cases as well. Understand the comments on the oil pump. Whole system needs to be cleaned. Do you guys use kerosene for this type of cleaning process??

  8. #8
    HORSEPOWER JUNKIE 9secZO6's Avatar
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    Man, this 1 ain't hard at all........the chain let loose, when it did, it took out the bendix very easily, and because the motor was spinning faster than idle (had to be) the oil pressure pushed the tensioner into the carnage as it was happening. Bad mutha freakin' day at any rate. Chains fail not just from interference, but harmonics as well. The starter teeth did not break and cause this....unless a tooth nicked the chain when it was started at some point. When running, the bendix gear touches nothing.

  9. #9

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    Quote Originally Posted by mitch411RXP View Post
    Hydro lock would bend a rod not break the chain been there before.
    your right after i thought about it that made no sense at all.

  10. #10
    You got lucky that is didn't hit a valve right when it broke.When I've had my cam out the valves all go close from spring tention.

    That is what I was saying is a tooth damaged the chain.I don't think the chain can hit the the gear and by what he said there is no valve damage.I don't think it was very high RPM's.

    You also need to check the cases to make sure the chain didn't break the ear of the case that goes under the chain.Also check the teeth that drive the chain on the crank.If a tooth did that then there might be some damage there.
    Last edited by mitch411RXP; 01-24-2008 at 12:05 PM.

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