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  1. #1
    Join Date
    Apr 2003
    Location
    Eastern Shore, Va.
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    2,310

    Default 350 - Bad valve? Lifter?

    The PCM/Sea Maxx 350 in my boat seems to have gotten louder at the exhaust on one side. It sounds like there's something going on with just one cylinder. The sound is almost unnoticeable someone else might not even hear it but I notice it because I just know what this motor "normally" sounds like.

    Anyway, at first I thought it might be a burnt exhaust valve or seat, but in discussing it with a friend, he suggested it might be a stuck/deflated lifter.

    I put some Marvel Mystery Oil into the crankcase (and also the intake) to see if that might pump up a dirty lifter but I don't notice any difference, yet.

    Can anyone give me any tips on how to diagnose this? I have a stethoscope and a compression tester, and I should probably buy a vacuum gauge (would that tell me anything?) ...

    Engine is:
    2000 PCM Sea Maxx 350 w/ 310 hp
    throttle body injection
    raw water cooled

    Thanks in advance for any help.

  2. #2
    Join Date
    Mar 2010
    Location
    Shirley, New York
    Posts
    587

    Default

    do a compression test, burnt valve = bad compression

  3. #3
    Join Date
    Jan 2003
    Location
    Russell Springs, KY
    Posts
    2,294

    Default

    Other than being "louder", does the engine run any differently? Like a miss?

    The last time I had one start running louder, it was the exhaust riser(s) had become plugged with rust, so the exhaust was no longer being cooled properly. The spray of water from the riser causes exhaust gasses to expand, cool and become quieter at the exit. Eventually, the hose failed right at the riser from the extreme heat, then it got REALLY loud LOL.
    Tow, Tow, Tow your boat.....

  4. #4
    Join Date
    Dec 2008
    Location
    Atlantic City, NJ area
    Posts
    9,754

    Default

    Regularly run engines that have their oil changed on a regular basis rarely have stuck lifters. Not never. But I would go with Don's idea if it is still running smoothly. A stuck lifter is going to cause it to rumble pretty badly at idle.
    1982 20' Cuddy Cabin, 2012 Rebuilt PCM 351 .060 o.s.pistons, Gt-40 heads FWC 1/2sys Edelbrock carb

    Old Coast Guard motto: YOU HAVE TO GO OUT BUT YOU DON'T HAVE TO COME BACK!
    That should be every boater's warning. Be safe out there!

    Disclaimer: Any comments made in these posts are just suggestions.... learned from the School of Hard Knocks.... Class mascot: A Knucklehead

  5. #5
    Join Date
    Apr 2003
    Location
    Eastern Shore, Va.
    Posts
    2,310

    Default

    Quote Originally Posted by GRUMPY SEA DOG View Post
    do a compression test, burnt valve = bad compression
    Thanks. If it doesn't smooth out, I'll do a compression test.

    Quote Originally Posted by Capt Don View Post
    Other than being "louder", does the engine run any differently? Like a miss?

    The last time I had one start running louder, it was the exhaust riser(s) had become plugged with rust, so the exhaust was no longer being cooled properly.
    Thanks Capt Don, I hadn't even considered that. It's kind of like a very, very slight "miss" ... as if just one out of the 8 cylinders is very slightly louder than the others.

    Quote Originally Posted by Ship View Post
    A stuck lifter is going to cause it to rumble pretty badly at idle.
    THanks, Ship. I guess I'll rule out a stuck lifter (it's not that rough).

  6. #6
    Join Date
    Jan 2008
    Location
    Bensalem PA
    Posts
    6,036

    Default

    VACUUM GAUGE ....... Yes it's is easier to attach a vacuum gauge to a pure vacuum port than to pull plugs for a compression test ..... A steady reading = no valve problem ..... Flutuating rapidly = problem then do a compression test to find the cylinder...... Then a dry/wet test

    Collapsed lifter clacking like hell ..... Can't miss that sound

    Something with the exhaust ........ good possability

    If you had a dead cylinder it would be running rough and exhaust note would be heard clearly different


    Thats my .02
    Amber Leigh

    2003 246 CC Gelding
    350-330 mpi cap's choice


    Cum catapultae proscriptae erunt tum soli proscripti catapultas habebunt. It's Latin


    Disclaimer:I am not responsable for the accuracy made in these posts ..... IANAL

  7. #7
    Join Date
    Jan 2003
    Location
    Burlington, New Jersey
    Posts
    178

    Default

    I would do a compression test. My Sea Max 350 blew a head gasket between #3 and #5. It could be just starting on yours. Even with the bad gasket, the engine ran well at idle, but around 2500rpm there was definitely a sound. It was in the water so I really could not hear any louder sound at idle. It was 2 years ago, I pulled the head and cleaned it up with a premium gasket and it's been fine ever since. That was 250 hours ago. Good luck.

  8. #8
    Join Date
    Apr 2003
    Location
    Eastern Shore, Va.
    Posts
    2,310

    Default

    Thanks again, guys. This helps me a lot.

  9. #9
    Join Date
    Jan 2003
    Location
    Bayport, New York
    Posts
    1,244

    Default

    Did you check your exhaust gaskets? Sometimes they sound like valve issue but there just exhaust manifold gasket leaks.
    Rich
    "If you are lucky enough to own a boat, you are lucky enough"
    Rich, 1989, 22' Cutty Cabin, Indmar, 351 Ford, GT-40-P heads, FWC, Edelbrock 4 brl.
    Bayport, N.Y.

  10. #10
    Join Date
    Feb 2003
    Location
    Egg Harbor Township, NJ
    Posts
    1,192

    Default

    This evening, I started to diagnose a similar problem with my 351. The one side just doesn't sound quite right. After running a few minutes, there is one exhaust port at the manifold that just seems too cool to the touch. Coincidentally, it the same cylinder that I had trouble with shortly after installing these heads last spring.

    Anyway, here is my plan for tomorrow. I'm going to run the engine again (on the hose, the boat is still on the trailer) until it is fully warmed up then check each exhaust port with a temperature gun. I have already pulled the rear two plugs, and the one on the "cold" cylinder was sooted up pretty well.

    If I find the cylinder to be dead, as indicated by a cooler exhaust, then my next step is to remove the exhaust manifold and valve cover and have a look at the exhaust valve, exhaust port and the rockers/lifter for any problems or unusual colors. I will also perform a compression test at this time to see if the cylinder has low compression. My theory is that one of the valves has some problem which is affecting compression and proper combustion. I already verified spark to that cylinder.

    Per my signature, I have Hy-Tek manifolds. While I love the stainless steel durability and the added power these provided, I also learned tonight that it is impossible to do a compression test due to the very close proximity of the plugs to the manifolds. There was no way I could get my tester in there, which forces me to do some diagnostics out of order.

    I wouldn't be surprised if the port side head has to come off for further inspection.

    And the more I think about this situation, before I had the problem with the rocker arm on this particular cylinder the boat really flew at WOT. After the rocker came loose and I corrected the problem, I seemed to have lost some speed at WOT. I attributed that to a dirty bottom and old ignition wires. But if that cylinder did go dead at that time, I'd be down 12.5% in power which might just be where the top end speed went.
    1976 20 Open "Angel"
    351 4bbl, Hy-Tek manifolds, K&N Flame Arrestor, Pertronix Ignition, RWC but always flushed.

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