If Bottom End Passes Comp Test Should I Not Rebuild It?

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by foxbody1989, Oct 12, 2013.

  1. If bottom end passes compression test should i not rebuild it? Hi I'm on a budget here and I here some noise coming from my heads and I'm burning oil pretty good so ? is if I pass a compression test could I just worry about freshening up the top end? unknown miles on bottom end. This might be a rookie ? but I'm still new. I have around 1k to spend I have twins on the way and military so budget is key.
  2. A compression test will help to determine the overall health of the engine when related to piston ring seal. Oil consumption can be related to that, or from the valves/seals in the heads. Since it is so easy, go ahead and do the test. Remove all the plugs first, block the T/B open, and crank the "tested" cylinder 3-4 times until there is no additional movement of the needle on the gauge.

    If the reading is consistent between cylinders, (w/i 10% of each other) and depending on the overall pressure,... then the bottom "checks out".
    W/A engine using oil, you're probably gonna have a low cylinder(s).
    Problem is, The test can point to leaking upper or lower causes (or both).

    Go to your base auto hobby shop and see if they have an engine leak down tester. If they do, see if one of the old guys running the place knows how to use it. It is a far better "test" to find out what is really the problem in the engine. W/I, you'll be able to pressurize each cylinder, and listen to the air escape either into the crankcase, or past the valves into the intake manifold

    Regardless, 1000.00 could fix either cause, but it'll be a budget fix at best.
    i.e. You'll be able to pull the heads and pay a machine shop to rebuild them to new specs, and re install the heads, W/ alot of money to spare, and....

    You may be able to tear the bottom down for a basic refresh, to include a hone, and re-ring. Add new bearing,s a timing chain, oil pump, and pick up tube, w. all the requisite gaskets, and put it all back together.

    I know that I could do it,..question is...can you? While not hard,...it does require a certain ethic, a space to do it, and leave it while it is happening, and the right tools. If you don't have access to any of these things,..I'd make sure I did before I ever removed the first spark plug.
    7991LXnSHO likes this.
  3. I couldn't have said that better myself Mike. I agree 100% ^^^
  4. Thanks I will start with the compression test. And good call on base auto hobby I will call them and check if they have the tester. I also have a garage so have the area and could follow a manual. I will keep updated what comes out of this all might be awhile though.
  5. Mad Mike, that answer showed why you have a blue ribbon.
    I hate to tell the OP, but if one of these modern V8 motors is using significant amounts of oil, you will be only doing a band aid by not just going through it or getting a cheap crate motor. This is not like when flatheads or old lawnmowers that had bad quality rings to begin with and needed re ringed periodically. If it does not pass the compression or leak down, consider it a wise use of money to just do it all ONE time.

    There are other clues to hint where oil is going. If it smokes on deceleration, after parked on an angle, or on being shut off for a bit, it is likely from the valves or stem seals. If it smokes on acceleration, think rings and pistons. If it smokes all the time, get some nicotine patches. Actually, save up for a complete budget rebuild then do the tests to confirm.
  6. I suppose rebuilding the heads could be compared to putting new alluminum heads on a good bottom end. But what wears out the valve guides wears out pistons and rings too. I still say it is band aid fix you may regret.
  7. So here is the results 1-8 200,190,185,180,190,170,190,190.
  8. that's awful high compression numbers for a stock motor, especially one that's burning oil. I'd expect 150-170. Did you do it cold or hot? Are you sure the bottom end hasn't been rebuilt?

    Regardless, seems #6 is the problem. Squirt some oil in the spark plug hole and re-run the test. If the number goes up tot the others, your rings are worn.
  9. Sorry didn't mention if it was stock or not. Just don't know if anything has been done to the bottom end I do have h/c/I headers etc. I did it why it was warm. I put a little oil in it and went to 180.
  10. Did you pull all the plugs and the coil wire before doing the test? With those numbers I would be inclined to think it's the valve seals.
  11. Yes I did. I know im running rich as I can smell gas strongly but as I was watching the exhaust today it had steady light white smoke and looked like water possibly condensation. But I'm not running hot or loosing water but smoke is always there. Not sure if this is important but it does have nitrous I have never used it but it is there not sure if its been sprayed a billion times or not.
  12. A steady light white smoke is not an indication of excessive fuel,...it is more of an indication of a head gasket water leak.

    White smoke= water
    Blue/grey smoke=oil
    Black smoke=excessive gas

  13. listen to this guy he knows a thing or two about a thing or two... but i guess when your as old as he is you pick things up over the years
  14. Either that or they elected a new Pope.
    90lxwhite likes this.
  15. Well yes,..there is also that to consider when your mustang is steadily emmitting white smoke. Maybe your car has some sort of attachment to the Vatican.
  16. Sounds like it is time for the leak down test to confirm where the oil is going. I would suspect if there is a head gasket leak that involves the compression chamber, the leak down test may send bubbles into the coolant system. It could also leak from a coolant passage into an intake port, and that will not show on a leak down test.
  17. HA!