Leaky intake valve Dx.

Discussion in 'General Discussion' started by dvx216, Feb 10, 2019.

  1. dvx216

    dvx216 Well-Known Member SILVER Sponsor

    Feb 1, 2012
    orrville,ohio
    2000 310 sundancer 5.7 vdrives






















    n/a
    twin 5.7 300 Hp. V drives
    Made a trip up to my boat and talked to my mechanic. He showed me my old heads and He said if he had to guess what happened to them was to big of a load in the boat and pre-detonation which caused the valves to burn. Two of them had burned into the seat and the main one causing the leak was no longer round.
     
  2. PlayDate

    PlayDate Well-Known Member SILVER Sponsor

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    Really.....on a EFI engine?

    For that to happen.....something else had to be wrong. The ECM controls pre-detonation with the knock sensor and will retard the timing to protect the engine. What causes valves to burn is a lean condition not pre-detonation. Do you have some pictures you could share of the heads and valves.

    I'm not saying your guy is wrong but something doesn't sound right. Were there any set codes in the ECM?
     
  3. dvx216

    dvx216 Well-Known Member SILVER Sponsor

    Feb 1, 2012
    orrville,ohio
    2000 310 sundancer 5.7 vdrives






















    n/a
    twin 5.7 300 Hp. V drives
    I agree a hundred percent but it is what it is and the physical damage is still there. When this thing reared its ugly head and in my own digging I found bad spark plug wires not sure if that was the cause of the problem
     
  4. PlayDate

    PlayDate Well-Known Member SILVER Sponsor

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    Bad wires turn the plugs black since some firing is occurring. The ECM should have seen misfires if that was the case. I'm just curious what caused it. I haven't seen a knock sensor go bad but something isn't right. Some pictures would be great and so would a look at any set ECM codes.

    If the combustion chambers with the burnt valves are light gray.......then I would be concerned about it happening again.
     
  5. dvx216

    dvx216 Well-Known Member SILVER Sponsor

    Feb 1, 2012
    orrville,ohio
    2000 310 sundancer 5.7 vdrives






















    n/a
    twin 5.7 300 Hp. V drives
    No discoloration in the chamber but there was a small chip out of the intake valve face that was leaking. If you search the internet you can find millions of reasons what might cause this but not definitive.
     
  6. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    How normal do the piston tops look ?
     
  7. PlayDate

    PlayDate Well-Known Member SILVER Sponsor

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    True.... but I don't rely on the internet when I have 30 years building/repairing engines that's why I asked about pictures. It is your boat....I was just trying to help you avoid another repeat when you get it back together.
     
    techmitch likes this.
  8. dvx216

    dvx216 Well-Known Member SILVER Sponsor

    Feb 1, 2012
    orrville,ohio
    2000 310 sundancer 5.7 vdrives






















    n/a
    twin 5.7 300 Hp. V drives
    Talk to my mechanic again after reading all your thoughts a lot of red flags went up. I had miss understood my mechanic when I asked him for what could cause this and those were the things he said could do this. What he saw with my heads because there was no discoloration on the pistons or chambers that something went through the valve and did the damage.When he seen the damage to the valve he rolled the piston to the bottom and checked for any damage to the cylinder and there was no signs of scaring or oil leak by.If this was one of my smaller boat that were on a trailer I would have done this job. It's hard for me to let go and trust someone to do this kind of work. This mechanic was recommended by a friend in the marine business up in the Catawba Is. area. I did ask him about the ECM and anti knock sensor his response was a no knock sensor will not protect a motor from pre detonation from bad fuel because this sensors if for ignition control not combustion. Predet. happens and the damage is done before the ECM can act. Thank you all for your input I learned a lot and have peace of mind because of it.
     
  9. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    There you go....new heads or valve job and go boating, I wouldn't over think it either
     
  10. PlayDate

    PlayDate Well-Known Member SILVER Sponsor

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    So....I'm the only one who wonders what "went through the valve" to cause the damage?

    And your mechanics answer is: "bad gas caused pre-detonation" on a fuel injected engine and he didn't bother to check the ECM for codes because he knew what it was.

    Okay....as I said...your boat, your money.

    What I do know is I would have the your gas tested to either prove his thesis or not. My bet is that it has nothing to do with the gas but there is an easy way to tell. Pump some out and have the octane checked. If he is right....no harm no foul.

    If the gas is good....I would be concerned what caused this problem in the first place. If you don't find the problem....there is a good chance it will show up again.
     
    Rusted Nut likes this.
  11. dvx216

    dvx216 Well-Known Member SILVER Sponsor

    Feb 1, 2012
    orrville,ohio
    2000 310 sundancer 5.7 vdrives






















    n/a
    twin 5.7 300 Hp. V drives
    I guess you can insinuate all you want but testing the gas that's in the boat now has nothing to do with the motor when it happened last season and I didn't say anything about not checking the ECM or codes now did I. You might want to read my last post where I said I miss understood him about what he thought happened to my intake valve.Since you are a Master ASE wrench you also know that head damage without signs of discoloration, tulip valves or burned valves but a chip out of the a intake valve causing a bad compression test where the ECM checks out ok you then come to the conclusion the some thing physical damaged the valve . I've been wrenching for ever and also have a son that was a ASE master mechanic and his thought with a chip out of the intake valve face does points to something going through the valve.
     
  12. PlayDate

    PlayDate Well-Known Member SILVER Sponsor

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    I'm really not insinuating anything. Both of us have been on CSR a long time. The majority of problems that show up on CSR are what I call "mid-stream" which means you don't know the history before the problem occurred or what actions were taken to address it. So....two types of suggestions/questions follow: 1) ideas people have 2) people who try to understand the history and suggest things that line up with what they have experienced.

    I'm in the latter category. Like any other trade profession, marine mechanics suffer from 50% of them are good and 50% of them are bad.....the trick is telling one from the other. Most people rely on recommendations in the same way they deal with roofing contractors or other tradespeople. Nothing wrong with that but if it was foolproof....no one would post a problem on CSR.

    I judge mechanics by how they diagnose problems. If they routinely follow a path.....it is rare that they make nonsensical comments. Sure you can have weird problems but marine engines are pretty straight forward. You started this conversation with two burnt valves and one damaged valve. My mind goes to "how did this happen" on a modern fuel injected engine?

    Why? Because if the Intake Valve had a chunk out of it....it would have been backfiring through the intake on every cycle. Further, a compression check would have shown the dead cylinder and a leak down test would have shown something was wrong with the intake valve. Sometimes intake valves stick and make contact with the piston. When that happens they usually deform the valve but in other cases repeated contact will cause a valve to fracture. The latter appears to be what may have happened and the fractured piece went out the exhaust without causing further damage to the cylinder. That is extraordinary luck since it usually embeds in the piston or disintegrates and scores the cylinder walls since the valve steel is harder than cast iron or aluminum.

    As to the burned exhaust valves.....that is more of a mystery which may be related to the injectors on those cylinders since only two exhaust valves out of 8 had the problem.

    Just my thoughts......
     
  13. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    If this was my 20 year old engine, I'd go thru that fuel system from A to Z, replace all rubber lines and have the injectors serviced. Check the screen in front of the fuel pump and make sure your fuel pressure is where it should be at all rpm's
     
    PlayDate likes this.
  14. ttmott

    ttmott MS/PhD in OCD GOLD Sponsor

    Apr 3, 2012
    Space Coast Florida
    2006 52 Sedan Bridge
    Cummins QSM11
    And - in production engines, valves simply do not get "burned" unless they are hanging open or are bent or cracked allowing hot gas flow over exposed sharp edges and thin sections. There obviously was issues with the valves and their sealing before they became burned.....
     
    PlayDate likes this.

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