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ICE: Bad knock suddenly developed

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by djimbuser, Dec 28, 2023.

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  1. djimbuser

    djimbuser Junior Member

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    I thought it was the diesel truck next to me at the gas pump. Here's a video (with audio) of the knock:


    No engine codes still performs ok. 297k miles.

    Sounds like something right under the valve cover. Is it serviceable?
     
    #1 djimbuser, Dec 28, 2023
  2. Tombukt2

    Tombukt2 Senior Member

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    To be clear you're converter is in place? I can't remember the valve arrangement on this engine but I think they're adjustable or you've got a bucket sticking or something That's what it sounds like so the cam is coming to the high spot pushing the bucket down if that's the arrangement and then the cam keeps on going around back up to the low spot and the bucket takes a few milliseconds too long to pop back up or something along those lines so the engine was dead quiet an hour ago or something in that realm?
     
    #2 Tombukt2, Dec 28, 2023
  3. pasadena_commut

    pasadena_commut Senior Member

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    Especially if it sounded like that at startup but did not at the previous turn off. If it started making that noise while driving it is probably something else. (Or maybe a new hole in the cat?)

    We ask because:



    not sure what a missing cat sounds like under the hood, but your recording is pretty close to the one above.
     
    #3 pasadena_commut, Dec 28, 2023
  4. Tombukt2

    Tombukt2 Senior Member

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    Yours sounds a little more valve train like You don't have the throatie exhaust sound but I just had to ask I think it's one of the shim over bucket doodads under the valve cover in the Prius you could take the valve cover off put the front rocker covers on jack stands and have somebody put the car in drive. Don't touch the gas just let it start to roll around and you be outside of the car with the valve cover already off because the reciprocating mass is going to start to turn as soon as you take your foot off the brake in drive. And you'll be able to watch the cams turn around and you should hear the sticking and you should be able to see it and then before it starts to make a mess and blow oil all over the place press the brake put it in park shut it off I guess remember which one it was.
     
    #4 Tombukt2, Dec 28, 2023
  5. djimbuser

    djimbuser Junior Member

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    The cat is in place.

    I took the valve cover off and didn't see anything alarming (no metal shavings or the like). Image: https://photos.app.goo.gl/EUmHUo6oC5vrwbhi8

    I rotated the engine by hand to watch the cups go up & down. I removed the spark plugs and took photos of the pistons/cylinders with a snake camera. I installed new spark plugs and reassembled it.

    This time I put the car into maintenance mode and recorded revving the engine a few times. The sound appears to mostly just be at idle. Further thoughts please?

     
    #5 djimbuser, Dec 28, 2023
  6. Tombukt2

    Tombukt2 Senior Member

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    It does seem to sound as though it's more pronounced at low RPM or idle so that makes me think even more something that could stick and click at idle that would be in the valve train generally but with the flex plates and the things going on here in between the engine and the transmission and one of my generation 3s I believe this is what's happening right now but the sound is quite a bit different I wouldn't expect anything in my bores more piston holes to beat having anything to do with his issue If anything got in there it would get crushed up and mangled and then would have dents in the top of the piston and possibly a whole then really bad running but not necessarily a whole lot of noise A connecting rod could be making kind of a similar noise but it's usually more of a ticking that gets faster with speed whatever's going on here is definitely attached to the reciprocating mass It just seems to float to a spot where it stops being so pronounced when you get to I don't know 1800 or so RPM is what it sounds like I don't know if there's an inspection cover that you can undo so you can see the bolts or see the back side of the flex plate and I don't think there's a way to get your camera in there in the front of it I don't I'm not sure of that but who knows but that is interesting and seriously sounds like the valve train to me but you would have to catch it sometimes you can run the crank bolt around by hand or by electric wrench or something You may have to have it at you know 50 or 80 RPM for it to happen possibly You got to give it time for it to hiccup as the cam goes around
     
    #6 Tombukt2, Dec 28, 2023
  7. djimbuser

    djimbuser Junior Member

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    I drove it again last evening. It's not consistent with RPM rather more consistent with the engine "call for power". What I mean by that is if it's idling at a light or accelerating from 60mph to 70mph on the highway uphill it makes the sound (ie, even at higher RPM)... However if I let off the gas pedal and at speed if I just touch the brake pedal (ie, not brake just enough so the car knows I'm slightly pressing the pedal) the noise stops completely immediately.

    I've seen videos on the clutch/dampener creating noises however it doesn't appear that the Gen2 even has one of these (dampener videos are all on Gen3's).

    Although from under the engine bay it really sounds like the noise is coming from under the valve cover the "click" is so loud it's hard to believe one valve could make this much noise? The sound echo's off the pavement below the car so that leads me to believe it may be something closer to transmission and the noise is just being communicated through the engine bay and sounding like it coming from the top of the engine.
     
    #7 djimbuser, Dec 29, 2023
  8. Tombukt2

    Tombukt2 Senior Member

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    Use a long screwdriver or extension and listen along the valve cover put the other end of the metal bar to your ear or a mechanic stethoscope and you really got to get a handle on this pretty quick or else.
     
    #8 Tombukt2, Dec 29, 2023
  9. djimbuser

    djimbuser Junior Member

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    Stethoscope on order with a-prime.. I should get it tomorrow.

    I would like to include the information that as of a month ago I did start noticing some small level of heightened noise (ticking) but it wasn't terribly loud at all - it motivated me to check the oil and take it from half to full. Then no change at all until yesterday.

    I have the service manual.. what about camshaft timing gear assembly.. Would it be capable of making such a noise?
     
    #9 djimbuser, Dec 29, 2023
  10. Tombukt2

    Tombukt2 Senior Member

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    When you have the valve cover off you'll have access with a light to see a lot of this business and to be able to spin it around either with the car on jack stands and somebody sitting in the driver seat putting it in drive but giving it no gas reciprocating mass will be turning engine crankshaft all of it so there's always that you want to look quickly so you're not slinging oil everywhere.
     
    #10 Tombukt2, Dec 29, 2023
  11. rjparker

    rjparker Tu Humilde Sirviente

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    It has one. They rarely fail on a gen3 with a leaking hg much less a gen2 without hg issues. But as these cars age we can expect to see more “unusual” issues.

    I think the noise is just masked at higher rpm’s by normal engine noise.
     
    #11 rjparker, Dec 29, 2023
  12. djimbuser

    djimbuser Junior Member

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    The noise is very present in idle & in park. If I want to run it with valve cover off I can put the car in maintenance mode which just essentially (for my use) makes the motor never turn off.

    I removed the passenger wheel and plastic cover to expose the pully then quickly realize I needed to remove the spark plugs to release compression so I could spin the engine over with a corded drill.

    To my surprise: no noise. It's turning over plenty fast for the noise to happen I believe.

    Here's the video:



    I do see the transmission input damper in the service manual now. The noise just doesn't seem to come from down there. Also the frequency of the tick seems way slower than one crankshaft revolution.
     
    #12 djimbuser, Dec 29, 2023
    Last edited: Dec 29, 2023
  13. djimbuser

    djimbuser Junior Member

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    From my last post it would seem the sound only happens with compression. I tried starting the engine with one spark plug completely removed and the sound was still present for each individual plug removed. I also compression tested the cylinders and got:

    Passenger side (1) - ~93
    2 - 100
    3 - 135
    4 - 100

    What difference would compression make relating to the sound? a) more downward force on the piston that's compressing, b) more force on head gasket. Is it possible the sound is just air shooting out past the head gasket? Of course seeing in the back is pretty difficult with the exhaust manifold in the way & the cover shroud but I couldn't detect any air flow coming out the front side of the head.

    Service manual: Standard compression pressure: 128psi, min 99psi, max delta between cylinders: 14psi
     
    #13 djimbuser, Dec 29, 2023
    Last edited: Dec 29, 2023
  14. Tombukt2

    Tombukt2 Senior Member

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    That is way down I guess that could possibly cause an imbalance in the reciprocating mass as it is spinning Not sure of that but certainly would seem like it could because the way the engine is matched to the electric motors and all that works you know being way over the 14 lb allowable difference It's possible it could knock it off kilter a little bit I would think not but an older engines and drive lines that aren't as sensitive it wouldn't rear it's ugly head but here things are quite differently balanced it seems but I wouldn't think it would be that but it certainly could be I would say that engine has seen better days
     
    #14 Tombukt2, Dec 29, 2023
  15. rjparker

    rjparker Tu Humilde Sirviente

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    I am not sure a drill will spin it at high rpm like the motor generator does.

    Compression does not look good if it was done right. A gen3 is 157-199 psi with each cylinder within 14.2 psi of each other. The test procedure on a gen2 is essentially the same.


     
    #15 rjparker, Dec 29, 2023
    Last edited: Dec 29, 2023
  16. djimbuser

    djimbuser Junior Member

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    Here's the Gen2 manual page regarding compression testing: https://photos.app.goo.gl/E7tSLvm8BrbnG48d9

    When I spun the engine with a drill there was nothing in the spark plug holes (which is also the only way I can spin the engine over with a drill).

    For compression measuring I actually started the engine with three plugs installed. I do not have one of those fancy testers that can put the car into "Compression Test" mode.
     
    #16 djimbuser, Dec 30, 2023
  17. rjparker

    rjparker Tu Humilde Sirviente

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    So according to the above on gen2 it should be 128 psi with a 99 min. Each cylinder within 14 psi of each other.
     
    #17 rjparker, Dec 30, 2023
  18. djimbuser

    djimbuser Junior Member

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    Yes, that's what I wrote in post #13: "Service manual: Standard compression pressure: 128psi, min 99psi, max delta between cylinders: 14psi"

    And pouring some oil into the cylinder can help differentiate where the leak is coming from piston rings or valves (assuming head gasket is ok).

    I cannot spin the engine with the drill to test compression without injuring myself so I went ahead and turned the car on and re-did the tests more according to the manual with all spark plugs removed and testing one cylinder at a time with the tester. I got much better results for reasons I can't really explain:

    With "1" being passenger side:
    1: 155
    2: 145
    3: 145
    4: 150

    Next I installed spark plugs and snugged them down and recorded it. I think it's pretty revealing that the frequency of the sound is once per cam revolution:



    If just comparing the depression of the buckets the culprit would appear to be the right/front (#4) intake valves. Slowing the video down even more the sound happens after the #2 exhaust valves are opened. #4 intake is just slightly behind #2 exhaust it appears.
     
    #18 djimbuser, Dec 30, 2023
    Last edited: Dec 30, 2023
  19. djimbuser

    djimbuser Junior Member

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    I'm certain this is just worn out timing chain slap! Timing chain kit on order.. new guides, sprockets, chain, tensioner, etc on order. Looking forward to getting it installed.

    I'm happy that I took the time to measure compression and the learn the valve gaps are spot-on but I only wish I would have realized it was "just" the timing chain all along sooner instead of wondering if this beloved engine/car's life with me was over... better sooner than later though right?

    I hope this thread can help others.
     
    #19 djimbuser, Dec 31, 2023
    Last edited: Dec 31, 2023
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  20. djimbuser

    djimbuser Junior Member

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    Update: NOT the timing chain. Noise is due to the dreaded "Piston #3" with broken skirt and slapping. I haven't gotten the pistons out of the block yet so I don't know the condition of the other three however the cylinders look great so I'm going to try replacing piston #3 (and connecting rod/bearing and of course new rings).

    Hindsight is 20/20 I wish I would have removed the oil pan much sooner to discover the skirt parks. I used a snake camera from under the car to get a peek at cylinder #3 and I can see the broken skirt. I hope to have the pistons out soon.
     
    #20 djimbuser, Jan 12, 2024
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