Weird piston adjustment?

Discussion in 'Gen 3 Prius Technical Discussion' started by ddpr, Nov 26, 2021.

  1. ddpr

    ddpr New Member

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    2014 Prius v wagon
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    Three
    Background: My Prius V 2014 started to rattle and misfire #2 on about 188000 miles.
    Head gasket, I thought. Sure enough, coolant was disappearing but surprisingly oil level remained a same (it never eat any oil).

    So I opened it up - and there was a first surprise. #2 had oil and carbon soot (more than in any other three) in it and was not shining at all as it should be with a coolant leak. I drained the oil - and it was quite ok, not emulsified at all. (Well, I haven't drove many miles after the first sympoms showed up).

    I resurfaced the head in the shop and they tested the valves - no warpage, pressure holding ok. They didn't change valve gaskets though. Then I checked the pistons. And there it came another surprise: #2 is slightly lower than #3 (1/32 - 1/16). It looks more than the tolerance but much less if it was hydrolocked and the rod is bent. My bad, I haven't check the compression before opening it up (didn't have a gauge) so I don't know how was it. All pistons are free and not seized, no scratches in cylinders bore.

    Now I have to choose what to do next: 1) remove the engine and check/replace rods and the piston rings to see if the oil was coming up that way, 2) return head to the shop and ask them to replace the valve oil seals to make sure the oil doesn't seep down there or 3) just simply put the head back hoping that piston difference is within a limits and the leakage was caused by the gasket.

    I don't have much experience with toyota engines so I can't tell which scenario is more likely. I don't have a cherry picker though so I would try to avoid to pull the engine in order to get to pistons (although technically it is not very difficult as the unit is partially disassembled now).

    Also, as far as I understood from Chilton - the head bolts are reusable, right?

    Appreciate any suggestions.
     
  2. mr_guy_mann

    mr_guy_mann Senior Member

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    If there is a measurable / noticeable difference in piston height, then something is wrong. It might be just a little bit bent, but it's still bad. Modern engine controls can detect variations in cylinder output caused by things like slightly lower compression and throw codes.

    Who knows how long a slightly tweaked rod can last? I would go into it further (good time for new pistons and rings) or swap the engine.

    Posted via the PriusChat mobile app.
     
  3. Mendel Leisk

    Mendel Leisk Sand Pounder

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    There's a link in my signature for head gasket and cylinder head stuff. In that link one of attached pdf's has Repair Manual info regarding service limits for the head bolts. Cheap insurance (well not that cheap) seems to be to just replace the head bots though.

    That means pulling the engine, one way or another, sooner or later? It's very likely due to head gasket failure. The gasket regularly fails between #1 and #2, leaks coolant into either one, or both. Rolls Royce would be a new short block (around $2K), and refurb the head.

    Part numbers for the Toyota gasket kit (includes head gasket, valve seals, and pretty much everything pliable) and head bolts are in the attached.

    Addendum: I see the head bolt check pdf in link was missing some info, a second page. I've attached complete version here.
     

    Attached Files:

    #3 Mendel Leisk, Nov 29, 2021
    Last edited: Nov 29, 2021
  4. ddpr

    ddpr New Member

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    2014 Prius v wagon
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    Three
    Thanks for suggestions!
    Just a short update: talked to Gasket Masters guy. He said that he saw engines with 1/32 difference and a bent rod.
    (I was hoping for more significant difference and avoiding to pull the engine out. Ugh, I guess there is no escape now. But not really planning to keep the car afterwards)
     
    Mendel Leisk likes this.
  5. ddpr

    ddpr New Member

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    2014 Prius v wagon
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    Three
    Update and a question:
    I opened it up and the rod was indeed slightly bent.

    Now for the replacement - which are reusable parts? I guess the piston itself is. What about the pin, bearings and bolts? (Seems like a new original rod is coming with a new bearing and bushing anyway). Pin's snaprings marked non-reusable.

    Anything else I should be aware of? I plan to replace all the rings altogether as they are accesible now. Perhaps the oil seals in the head too, just in case. But I don't want to touch the crankshaft itself.
     
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