Intake valve stuck open??

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by LYSMO, Dec 20, 2020.

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  1. LYSMO

    LYSMO New Member

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    Has anyone ever experienced an intake valve stuck open? After readjusting my timing chain I discovered that two of my rocker arms were flying out from under camshaft no.1. I quickly realized that they weren’t even touching the cam lobes while the rest of the rocker arms were fine. As it turns out, the compression springs were measuring a little shorter than the rest. My first thought was broken pistons.

    I removed the intake manifold to discover that the pistons are straight as can be, but are stuck open. Has anyone experienced this before? Did anyone have any ideas on what could be the problem/how this can be fixed? (Preferably without removing the head, but I know nothing can be so simple with this car LOL)
     
    #1 LYSMO, Dec 20, 2020
  2. LYSMO

    LYSMO New Member

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    I’m wondering if moisture might have gotten inside at some point because I’m seeing something rust-like towards the top. This is the best pic I could get. What do you think?
     

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    #2 LYSMO, Dec 20, 2020
  3. mr_guy_mann

    mr_guy_mann Senior Member

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    If this was the engine that had the broken timing chain, then it is almost certain that several of the intake valves are bent. If the rockers are out and you can see that the valves aren't closed then it's 100%- the head will have to come back off, or consider getting a used engine. The pistons are in the cylinders of the engine block and go up and down. The valves are in the cylinder head and also go up and down (pushed open by the camshafts and closed by the valve springs).

    The timing chain keeps the camshafts synchronized with the crankshaft, so that the valves open and close when they should. If the chain breaks, jumps due to wear, or is installed incorrectly, then things go wrong. When the pistons are at the top and the valves are still open , they both try to occupy the same space. The pistons hit (and bend) the valves.

    The nail in the coffin would be to get a cheap flexible videoscope for a cell phone and look down the plug bore at the piston for shiny impact marks from one edge of the valve (looks like short thin crescent or sliver). Or you could apply pressurized air to the cylinder and confirm it rushes out of the intake ports.
    Posted via the PriusChat mobile app.
     
    #3 mr_guy_mann, Jan 9, 2021
    Last edited: Jan 9, 2021
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