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2010 Chrysler 300 – Low Compression In Single Cylinder

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here 2010 Chrysler 300 – Low Compression In Single Cylinder

This topic contains 5 replies, has 2 voices, and was last updated by Bryan Tift Bryan Tift 7 months, 4 weeks ago.

  • Creator
    Topic
  • #895979
    Bryan Tift
    Bryan Tift
    Participant

    Good afternoon all,

    I have a friend who has a 2010 Chrysler 300 with the 3.5L V6 engine in it. We were getting a misfire in Cylinder 5 and after new spark plugs and swapping coils, I did a compression test to find that all other cylinders had 160-170psi and the 5th cylinder had 40psi.

    I proceeded to do a leak-down test with about 90psi of pressure on the 1st, 3rd, and 5th cylinders (bank 2). All cylinders had a little air coming from the oil fill cap, as is usually the case, but with the 5th cylinder I heard air coming from the exhaust pipe and it wouldn’t hold pressure at TDC.

    I initially thought burnt exhaust valve, but upon pulling the head I noticed the valves didn’t look burnt. Now there was a good amount of carbon build-up, but what concerned me the most was the rocker arm assembly.

    All rocker arm and valves seemed to line up except for cylinder 5 exhaust valves. The rocker arm on those valves seems to have literally shaved about 5-6mm of metal away, even going as far as to cutting into the black bolt you see in the pictures. The rocker arm doesn’t fully seat over the exhaust valves. All other rocker arms can be moved and wiggled by hand. The 5th cylinder exhaust rocker arm cannot, and can only be moved with a rubber mallet. What this tells me is that that rocker arm is putting pressure on the valves, while the rest of the rockers aren’t putting any pressure. Since at a resting state the rocker arm seems to be putting pressure, I’m going to still assume that there is an incomplete seal on those exhaust valves.

    Pictures: https://imgur.com/a/1Ob5Uos

    Would this make sense? I think the car is due for a new rocker arm assembly, about $350 on Amazon, but I’m wondering if this is likely to solve my low compression on that single cylinder problem. Valve issues seem to be common on these engines and the valve clatter was loud when the engine ran. I took the entire cylinder head to a machine shop so I guess we’ll see what happens once we get a report back.

    I guess my question is, can this damage lead to an incomplete valve seat, leading to the exhaust leaking the compression? Did I make the right move?

    Thanks guys

Viewing 5 replies - 1 through 5 (of 5 total)
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  • #895980
    Nightflyr *
    Richard Kirshy
    Participant

    Without seeing the undamaged rocker assembly.
    This gap should not be.

    Something has happened..
    Either a locating shim / spacer or take up spring is missing.
    The rocker arm may be bent at this point.
    Besides changing the assembly, might be wise to check for a bent valve

    #895981
    Bryan Tift
    Bryan Tift
    Participant

    Yeah that’s what I’m thinking.

    Here is the original part: https://www.1aauto.com/dodge-chrysler-rocker-arm-shaft-assembly-mopar-4892293ac/i/mpech00001

    Notice how the left side has the huge gap because on the right side it started eating into the metal. It’s eating the screw now too.

    I’m getting a valve job done so I’ll report back on the shops findings to see what they say.

    #895982
    Nightflyr *
    Richard Kirshy
    Participant

    Judging by the pictures on line.
    It appears that perhaps due to bad lashing adjustment(s)
    May have caused the rocker arm to shift sideways causing excessive wear.
    That would explain the excessive gap.

    #895983
    Bryan Tift
    Bryan Tift
    Participant

    I believe the lash is preset as well, so no adjustments can be made. Another Chrysler failure?

    #895996
    Bryan Tift
    Bryan Tift
    Participant

    Machine shop confirmed exhaust valve wasn’t fully seating.

    They’re charging $110 for a valve job + any parts that need to be replaced.

    I’m going to get a new rocker arm assembly for $320. All in all not a bad price to do a major engine repair.

    Thanks for the help.

Viewing 5 replies - 1 through 5 (of 5 total)

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