Timing off after head gasket replacement

Discussion in 'Gen 3 Prius Technical Discussion' started by Steven Lake, Sep 26, 2025 at 4:31 PM.

  1. Steven Lake

    Steven Lake New Member

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    I replaced the head gasket on a Gen 3 2011 level 2 Prius with 240K on the engine because of antifreeze in the number 2 cylinder. When I tried to start it after the repair it ran like there was a misfire. I have read a number of threads where the owners had similar results and it seems that most of the problems resulted from the timing set improperly. When I set the timing I followed the instructions from the Toyota factory manual
    and verified all the colored links were in their proper location before I assembled the motor. Based on other stories that have read concerning head gasket replacement and setting the timing its hard to be 100% confident I did it exactly right. I should mention I pulled each spark plug and they are all firing.

    Other information:

    The engine does not run well enough to obtain a code from my OBD reader.

    I measured the piston height after disassembly and found no evidence of a bent rod.

    There is no evidence of new antifreeze leakage into any cylinder.

    All the spark plugs were replaced but I did not replace the coil packs


    Questions I have:

    What is the best method for checking the timing before I disassemble the engine again?

    What other things beside the timing being off can make the engine run like the timing is off? can any of the sensors do this?

    If I reset the timing I have read that there is a fixed number of rotations you can put the engine through where the colored links on the timing chain line up with the starting point marks again that verifies the timing is set properly. In reading about this there seems to be different numbers suggested for the number of rotations. What is the correct number ?

    Any other suggestions?

    thanks for your help
     
    #1 Steven Lake, Sep 26, 2025 at 4:31 PM
  2. rjparker

    rjparker Tu Humilde Sirviente

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    The most common problem is the timing chain off by one link usually caused by failure to rotate counterclockwise to release the tensioner.

    Sometimes the wrong top marks were used.



    Some have reported taking off the valve cover and verifying the cam marks with the timing mark on the harmonic balancer.

     
    #2 rjparker, Sep 26, 2025 at 4:51 PM
    Last edited: Sep 26, 2025 at 6:19 PM
  3. ChapmanF

    ChapmanF Senior Member

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    Depends on what you're counting. 70 turns of the crankshaft, or 35 turns of a camshaft, or 9 times seeing the same colored chain links go by, are all the correct number. :)

    Those won't necessarily be the same numbers for every type of engine. Somebody just has to count the sprocket teeth and chain links and do the math. These are the numbers you get for the Gen 3 Prius engine.
     
    #3 ChapmanF, Sep 26, 2025 at 5:01 PM
  4. ASRDogman

    ASRDogman Senior Member

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    You don't have to rotate the engine 30 times, just put the crank pully at TDC, and check the
    cam scrockets. Do the timing marks line up where they should? If then don't, rotate the crank
    360 degrees and check again. If the CAMS line up correctly, the timing chain is correct.
    It's not hard to setting the timing correctly. Toyota makes it very simple. They put the colors links
    on the chain!

    You only have to remove the valve cover. Very simple.

    You could keep rotating it, and hope you don't have to do it 30 times to get the links to match
    the sprockets, if you have nothing else to do.... Or if would give you peace of mind...

    If it's not running well enough, you SHOULD be getting codes.
    Are you 100% certain you have everything connected correctly?? Are you SURE you put the PCV
    valve hose on???? It is easy to miss that. You could just have a huge vacuum leak.

     
    #4 ASRDogman, Sep 26, 2025 at 6:58 PM
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