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Thread: Piston ring replacement

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    Default Piston ring replacement

    I just rebuilt the top end of my 260 engine. Head redone, headers etc.
    It is now making blue smoke. If I let it run in my garage the smoke actually burns your eyes. It seems to be gas rich?

    In any case I am getting some feeddback that maybe my rings are gone. I am going to look at doing a compression test. But two questions:
    Does this sound like rings.
    If I have to replave the rings can it be done through the bottom end with the engine in the car.

    Can I pull the oil pan and go in that way.
    I hope so my wife just got the garage back from doing the top end.
    Hate to see the look on her face if she sees an engine on a stand where her parking space in the garage used to be

    Glenn

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    NUTs according to wife ChrisZ's Avatar
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    And what about valve steam seals, are they new?

    I will suggest you make a leak down test first and if it show that you will have to change the rings, go talk with your wife.

    If you pull the head, it should be possible to replace the rings, while the block is in the engine bay.

    Chris
    -73 240Z HLS30-171039
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    Did it smoke before you rebuilt the head? If not, there would really be no reason for the rings to suddenly go bad.

    And you said it seems to be "gas rich" but then you focus on rings. It seems like a lot of work to replace the rings, only to find out you were actually running rich.

    If you have carbs it should be relatively easy to lean it out and see if things improve before you disassemble the engine.

    Just trying to help reason things out...

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    Registered User mlc240z's Avatar
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    Only thing is I've 'heard' that when you rebuild just the top end, it has a tendency since it's much tighter, to blow out the bottom end.
    Don't know if it 's true, but.......................
    Bart

    5/71 240z, HLS30-31306, mostly stock, ZTherapy SU's, Pertronix, Eibach ProKit, KYB, Poly bushings, 60 amp alternator w/Dave's plug bypass, headlight and parking light harness upgrades.

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    Default piston rings

    how do you do a leak down test. the head was rebuilt by a local engine shop. all guides etc were replaced. they said the original brass seal weere in it. in any case it did not blow blue smoke before the rebuild. it blows alot of smoke on acceralation. is it possible that it is fuel. I have adjjusted the carbs and the mixture nut is about a 1/2 turn from being screwed all the way in.
    I pulled the plugs and all 6 are black carbon. 6 bad cylinder rings is that possible. the bottom end is original as far as I know. You can see the crosshair grind in the cylinder bores so I assumed it was in ggod shape.

    any input / ideas / suggestions would be appreciated

    Glenn

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    Registered User Walter Moore's Avatar
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    Do you have a compression test kit? Most of those come with instructions for a leak down test. If the compression is good I would vote that it is just a mixture problem, but without testing it you don't know.

    Personally I twice replaced the rings in an engine that was still in the car, and I will never do that again. for two reasons:

    1. It was a lot harder than rebuilding it on an engine stand.
    2. Neither time did the engine work better afterward.

    If you have to "replace the rings" don't waste the time and money to do it without pulling the engine and taking it to a good machine shop for evaluation.

    Just my opinion...
    '71 240Z, Because any fool can drive fast in a straight line.

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    Quote Originally Posted by zdude1967 View Post
    how do you do a leak down test. the head was rebuilt by a local engine shop. all guides etc were replaced. they said the original brass seal weere in it. in any case it did not blow blue smoke before the rebuild. it blows alot of smoke on acceralation. is it possible that it is fuel. I have adjjusted the carbs and the mixture nut is about a 1/2 turn from being screwed all the way in.
    I pulled the plugs and all 6 are black carbon. 6 bad cylinder rings is that possible. the bottom end is original as far as I know. You can see the crosshair grind in the cylinder bores so I assumed it was in ggod shape.

    any input / ideas / suggestions would be appreciated

    Glenn
    Get your carbs dialed in first. Sounds like you are way too rich. Check to make sure the fuel pump isn't leaking fuel into the engine as well. Gas diluted oil is a bad thing. You are getting too much fuel from somewhere.

    Steve
    Last edited by doradox; 09-03-2010 at 10:00 AM. Reason: Fuel not oil
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    Quote Originally Posted by zdude1967 View Post

    - I just rebuilt the top end of my 260 engine. Head redone, headers etc.
    It is now making blue smoke.

    - in any case it did not blow blue smoke before the rebuild
    Looking back over this, these two statements logically suggest that the problem is in the head, if work was only done on the head. Valve seals installed wrong maybe?

    If it didn't blow smoke before and you only worked on the head and it blows smoke now, the head would be the first place to look.

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    Thanks to all for your help.
    I certainly would prefer a rich mixture to needing rings however I think I adjusted the carb as much as possible. I have the round dome
    Hitachi HGJ46W carbs.
    The mixture screw underneath is screwed in completely. I used a flow meter and matched everything. They lift at the same time etc.
    This is what is leading me to think rings as it blows a boatload of blue smoke on hard acceleration.However the exhaust can make your eyes burn.

    Am I missing something with the carbs? I understand that the head was shot, when I had it rebuilt, original brass parts etc. Is it possible that the former owner put a smaller needle in to improve performance due to the worn heads? Anyway I appreciate the help, put a lot of effort into getting it back together...my first time. The thought of having to break it all back down kinda sucks.

    Glenn

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    Registered User doradox's Avatar
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    Again, check for fuel in your oil. Does the oil smell like gas? If the carbs are right you shouldn't be running too well with the mixture screw all the way in.

    "Head redone, headers etc. "

    What was the "etc" that you did as well as the head and headers?

    Steve

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    Sticking chokes and valve steam seals is my best guess.
    Have you tried to lift a dome piston about 1/4 inch to see how it react?

    Chris
    -73 240Z HLS30-171039
    -66 Roadster SPL311-05204

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    Sticking jets might be the issue, as well as high float settings. I don't think the car should run with the mixture screws all the way in.

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    Assuming your plugs look black (with carbon) and not oily, then it's a fuel issue, not an oil issue. If you were leaking/burning that much oil, your plugs would probably be oily.
    Last edited by FastWoman; 09-03-2010 at 02:39 PM.
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    Thanks everyone for your suggestions. The Etc. was referring to a high capacity oil pump, new fuel pump, new hoses etc.

    I have done a lift test on the carb piston; it falls smooth and at what seems to be a reasonable pace.

    I will smell the oil shortly thanks for the suggestion.

    I put some Marvel Mystery oil in last night and took out for a hard drive. I discovered something that may help determine the issue. On hard acceleration, pedal to the floor very aggressive acceralation the car began to sputter, backfire from the exhaust, and generally run like crap.

    Ease off the pedal, give it a second or two and it stops and you can accelerate at a non-aggressive level and the car is fine. This happens over and over with the pedal to the floor acceralation.

    I hope this issue is the cause of the smoke as well.

    Anybody know what this is.... I guess this problem is either fuel or electrical but not mechanical such as worn rings are.

    Anyone???

    Thanks
    Glenn

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    Can be wrong oil in the dome
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    Rich mixture, reset your carbs. That involves checking for sticking nozzles, setting float level and doing the idle and syncing procedures.

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