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Thread: Smokes and misses

  1. #1

    Default Smokes and misses

    Giving it one last go in the M715 to straighten out my engine problems.

    Cylinder 6 isn't firing, and the plug is always covered in oil. Not sure if stuck ring or valve seals are toast.

    What can I do to troubleshoot which it could be?

    I've already poured Marvel Mystery Oil down the cylinder and let it sit 4 days, no real improvement.

    Thinking about adding half a quart of ATF to the oil and pouring the rest down the carb and giving it another hard run.

    Help!

  2. #2
    Join Date
    Sep 2014
    Location
    Wichita Falls, TX
    Posts
    603

    Default

    Maybe pull the valve cover and see what the valves on 6 are doing? Sheared some lobes off of a 350 cam once. Ran... poorly.. after that.

    Still planning on putting that bus engine in it?

  3. #3

    Default

    oil on the plug is a good indication that it is stuck rings. a leak down test would pin point it.

  4. #4

    Default

    I've had it off, adjusted the valves. Everything looked good.

    Traded the bus engine for a old school 454, no need to overcomplicate such a simple machine with EFI. Everything is about ready to put it in but the extra $500 or so to finish up isn't here right now. I'd like to enjoy it while there's some summer left, but other things take priority.

    Just ran 3/4 of a bottle of MMO thru the carb, smoked like hell, but it's still missing. My buddy tells me yank the head off and get a good look inside, but I didn't want to sink (more!) money into this engine just to swap it

  5. #5
    Join Date
    Sep 2010
    Location
    Middleville, mi.
    Posts
    1,245

    Default

    have you done a compression test on the engine?

  6. #6
    Join Date
    Sep 2014
    Location
    Wichita Falls, TX
    Posts
    603

    Default

    Quote Originally Posted by farmer View Post
    I've had it off, adjusted the valves. Everything looked good.

    Traded the bus engine for a old school 454, no need to overcomplicate such a simple machine with EFI. Everything is about ready to put it in but the extra $500 or so to finish up isn't here right now. I'd like to enjoy it while there's some summer left, but other things take priority.

    Just ran 3/4 of a bottle of MMO thru the carb, smoked like hell, but it's still missing. My buddy tells me yank the head off and get a good look inside, but I didn't want to sink (more!) money into this engine just to swap it
    I'm with ya on the EFI. And not wanting to dump money into it.

    Sure it's getting spark?

    We'll keep throwing darts till somebody hits a bullseye...

  7. #7

    Default

    dry compression test and then a wet test ? that's the only way I know of seeing if its a ring or valve problem

  8. #8
    Join Date
    Jan 2011
    Location
    Fernandina Beach, FL
    Posts
    3,689

    Default

    Quote Originally Posted by jokerwild12345 View Post
    dry compression test and then a wet test ? that's the only way I know of seeing if its a ring or valve problem
    True, a compression test would be possibly the first step.

    My experience:

    1970, Germany. 1968 truck assigned to me. I put 4000 miles on that truck in a year, all over Germany, so the truck was not very old then. It was a known issue with valve seals. The motor pool had them for replacement. If I didn't drive the truck at high speed, (heavy load, good and hot), it would foul a plug randomly. All I would do was to put one drop of oil on each port of the exhaust manifold, near the head and start the truck the oil would immediately start to smoke on any plug that was firing. The fouled plug port would stay wet. Pull the plug, flick the carbon whisker out of the gap and off we go!

    All of that said, if your engine has that problem, it could be fixed without pulling the head off. The compression test should head you in the correct direction.

    Please, let us know!

  9. #9
    Join Date
    Jan 2011
    Location
    Fernandina Beach, FL
    Posts
    3,689

    Default

    Quote Originally Posted by jokerwild12345 View Post
    dry compression test and then a wet test ? that's the only way I know of seeing if its a ring or valve problem
    A valve problem (smoking) would usually be a valve guide issue.

  10. #10

    Default

    Quote Originally Posted by Don Cavey View Post
    True, a compression test would be possibly the first step.

    My experience:

    1970, Germany. 1968 truck assigned to me. I put 4000 miles on that truck in a year, all over Germany, so the truck was not very old then. It was a known issue with valve seals. The motor pool had them for replacement. If I didn't drive the truck at high speed, (heavy load, good and hot), it would foul a plug randomly. All I would do was to put one drop of oil on each port of the exhaust manifold, near the head and start the truck the oil would immediately start to smoke on any plug that was firing. The fouled plug port would stay wet. Pull the plug, flick the carbon whisker out of the gap and off we go!

    All of that said, if your engine has that problem, it could be fixed without pulling the head off. The compression test should head you in the correct direction.

    Please, let us know!
    I have not yet done a compression test, but I did the oil on the manifold trick to determine it was cyl 6.

    I've tried getting it hot and really clean the cob webs out, but temp gauge doesn't get much past 160*, and its been in the 90s here. I assume the thermostat was pulled by the PO.

    I should probably get a thermostat and a compression tester, try to figure out whats up with cyl 6 then try to get it hot with the thermostat in.

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