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Hel, 98 Mitsubishi with the 3G83 engine smoking

Discussion in 'Mitsubishi Minicab' started by Jeff Brown, Nov 17, 2020.

  1. Jeff Brown

    Jeff Brown New Member

    Hello, new to the forum, I have a 98 Mitsubishi with the 3G83 engine, I bought it running fine with no issues other then it smoking. Prior to buying it, the engine was replaced and had sat for 8 years until the guy I bought it from sold it to me. He said all he did was clean the carb and put fresh gas in it and it started right up. I have since performed a cylinder leak off test and it showed a possible bad head gasket, cracked head or block, I pulled the intake and head off to find the 3rd cylinder very wet with oil residue in the exhaust manifold which would lead me to believe that cylinder is the issue. The head didn’t show any visible signs of a crack and gasket looked brand new, my question now is, do I drop the pan and pull the #3 piston to see if there is a cracked ring, assume it’s the head and send it to the shop to get reworked, cylinders look fresh, no wear lip or cracks that I could tell. All indications is that the motor has been rebuilt and has very few miles on it, but stumped at nothing obvious yet and looking for a direction to go. Any help would be appreciated
     
  2. Jim Nelson

    Jim Nelson Active Member

    As usual it's impossible to diagnose over the net but with it being as you describe you might take a close look at the valve seals on that one cylinder. Otherwise it could possible be a stuck or broken ring, though that's not too likely without some moisture getting into the cylinder and causing some rust. I always try to start jobs like this looking at the easiest and least expensive possibilities first then carefully working forward.
     
  3. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    If you hadn’t already torn into it, I’d say that you should do a leak down test to see where the air escaped to. You can usually hear or feel the air flowing out of a bad cylinder.

    Typically with a bad head gasket, they leak into the cooling system and you’ll get bubble in the radiator. Bad rings you can hear a whistle if you put your ear or a hose to your ear by the oil fill plug, or you can put a balloon on the dipstick tube and it will blow up a bit. Bad inlet valve seating can be heard at the carb, and a bad exhaust valve at the exhaust pipe.

    You say you did a cylinder leak off test. Was that a bleed down test with two gauges and an air supply, or a compression test with one guage?

    Not trying to talk down. We have a whole range of knowledge showing up on the site, from guys who were professional mechanics, to folks who aren’t quite sure what a spark plug is. And, when you’re trying to help trouble shoot things over the web, you need to get what level of skill and knowledge they have.

    I would go with Jim’s advice, and check the stem seals on the valves.

    Also, if you could go into your profile, and include the information on your truck in the signature line, it will help folks give you better advice in the future. If you look at mine, Limestone’s, or JTT3’s it will show the kind of information that helps.

    And, welcome aboard, Jigs.
     
    Last edited: Nov 18, 2020
  4. Jeff Brown

    Jeff Brown New Member

    The cylinder leak off test was with dual gauges, 100 had 100psi on it and the other 85psi, with the radiator cap off the air pressure started pushing antifreeze out of the radiator, and that is why I took the head off looking for the obvious. Head gasket looked great, I found nothing noticeably wrong other then the oil soaked exhaust off the #3 cylinder.
     
  5. Jeff Brown

    Jeff Brown New Member

    Could this be an issue?
     

    Attached Files:

  6. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    Definitely: You can see discoloration, where the coolant was flowing, and the pitting in the head from where the hot water in the coolant mix was expanding from the vacuum in the cylinder and boiling.

    I’m a bit concerned by seeing three valves with an “8” on them and one with an “A84”. I would expect to see two with the ‘8”, and two with the A84. As exhaust and intake valve are typically different. Even though they may be dimensionally the same, exhaust valves are typically a different alloy than the intake valve, because the thermal loads are very different. I recommend taking a good look at the other cylinders and seeing what valve markings you find.

    I’d recommend cleaning up the head with a good scraping, and then checking the head for warpage, and milling it down as little as possible to get rid of any warpage you might find.

    If the head is still true: Follow the good scraping, by a few light passes with some 800-grit wet or dry sand paper and a bit of light oil, cleaning it up and putting it back on.

    In my misspent youth, I used to apply high aluminum solids, high temperature epoxy spray paint to the mating surfaces, to seal the aluminum-asbestos-aluminum sandwich style head gaskets. Put some wadded up newspaper in the cylinders to keep the paint off, spray the top of the block, drop on the gasket, pull out the newspaper, spray the head, and torque it home with the paint still wet. Never had any leaks.

    New gaskets are typically a sandwich of teflon-aluminum-teflon, the manufacturers explicitly recommend against any type of sealant. I spray everything down with brake cleaner. Before assembly to get any grease or oil off the mating surfaces, and I’ve never had one leak.
     
    Last edited: Nov 18, 2020
  7. Jeff Brown

    Jeff Brown New Member

    I appreciate the feed back, since I wrote last I have had the head at the machine shop were all 6 intake valves needed to be replaced and had the head resurfaced and new valve seals installed. I think I will take your advise about spraying down the mating surfaces with brake cleaner and then with high temp epoxy paint before reassembly, as I have seen a lot of head gasket threads and seems to be a very common occurrence. I will keep you posted and let you know if my smoking issue is solved. Thanks for the help
     
  8. Jigs-n-fixtures

    Jigs-n-fixtures Well-Known Member

    Remember that you need to replace teh head bolts. I would expect them to be torque to yield bolts. Not sure where to get replacements though.
     

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