Leaky valve guide

Discussion in 'Domestics' started by Chaud, Apr 5, 2017.

  1. Chaud

    Chaud Full Member

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    Please fill out the following to ask a question.

    MAKE:pontiac
    MODEL:Firebird
    YEAR:1994
    MILES:195K
    ENGINE:3.4 L
    DESCRIBE ISSUE.... Engine burning oil and rough. Did compression test on all 6 cyl starting with #1. The reading in order are 155, 135, 130, 35, 110, 160. Next did the leak down test on #4 with 35 PSI pressure and found air coming out of the oil spout on cylinder head. I think it is from a leaky valve guide but could be something else. If my thinking is correct that it is a leaky valve guide then my question is what is the least I could do to get it running well and then sell. The next question is can I install sleeves my self or have to go to a machine shop. I will appreciate your guidance on it. Thanks-Chaud
     
  2. billr

    billr wrench Staff Member

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    Those low compression readings aren't because of worn guides. Do "wet" compression checks on all and post results, but that may be inconclusive. To get it "running well" is going to mean removing both heads and replacing/grinding any valves that don't seal. With the heads off you can do a leak-down style test that can be conclusive about the rings; and you decide how much deeper you want to get sucked in. How much is this '94 worth in your area? It may be more practical to sell it "as is"
     
  3. Mobile Dan

    Mobile Dan wrench

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    Where is the "oil spout on cylinder head" on that engine? If you mean "oil fill hole on valve cover", your next test would be a "wet compression test" to test for worn rings.
    [​IMG] [​IMG] [​IMG]
     
    Last edited: Apr 5, 2017
  4. Chaud

    Chaud Full Member

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    Thank you Billr and mobile Dan for your reply. Billr, After reading your comments I realized my conclusion that low pressure is due to leaky valve seal is wrong. Now I am wondering the air blowing out from the oil spout ( "oil fill hole on valve cover") could be coming from bad rings. The logic behind is that when 100 psi air pumped through the spark plug hole, it goes thru the rings into the oil pan and then comes out thru the"oil fill hole on valve cover". Please correct me if I am wrong. I did the wet test, compression reading increased from 5 to 10 psi on all 6 cylinders. Not a big difference. Real bad one #4 went from 35 to 40 psi. 2nd option is I could get a used engine from a junkyard for $400 with compression readings ranging from 150 to 180 but the engine is from automatic Trany and I have manual transmission. will that work? I live in San Diego area, this car may be worth $500 or less but I did not put on sale yet. Thank you again.
    Chaud
     
  5. nickb2

    nickb2 Wrench. I help when I can

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    Yes, an auto will fit a manual. Block is the same.

    If pressure did not increase any more than 5 psi with the wet test, than that cylinder has more than just worn rings. And this is wrong,
    A cylinder passing compression through a spark plug hole WILL NOT compress into the oil pan. However, I may have misunderstood the quote. If you inject shop air (100-120psi) through the spark plug hole, which is called a 'leak down test', yes, you will hear blow by through the oil filler hole if rings are finished, piston cracked etc. We use a leak down test to determine if compression is going into the coolant, the exhaust, the intake or into the base of the engine. It is a test to help determine the extent of repairs to be done to an engine.
     
  6. nickb2

    nickb2 Wrench. I help when I can

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    From here
    http://www.gregsengine.com/cylinder-leakdown-testing.html




    Problems are pinpointed simply by determining where the air is leaking out of the cylinder. Air leaking out of the exhaust system (you can hear it in the exhaust pipe) indicates a problem with the exhaust valve. Air coming out of the carb or throttle body indicates a bad intake valve or seat. Air going into the crankcase is leaking past the rings and does not indicate a problem if the percentage is low enough. A leak where the air is going into an adjacent cylinder or into the coolant indicates a blown head gasket or cracked head.

    A brand new street engine might measure from 5% to 8% depending on the engine, manufacturer, and degree of break in. A street engine that measures 10% to 20% per cylinder, although indicating some wear, if there is consistency between cylinders and if all of the air is leaking past the rings into the crankcase indicates a reasonable street engine for daily driving that does not need any immediate work. Any readings 30% or higher indicates a severe engine problem.

    Using the leak down test, especially in conjunction with a compression test, should allow you to quickly determine the basic condition of any engine. If you are not sure what the levels should be, differences in readings between cylinders is a key indication of a problem. These are tests that can and should be done by any competent garage. After testing, you will know whether the top or bottom end really needs a rebuild.

    A cylinder that has poor compression, but minimal leakage, usually has a valvetrain problem such as a worn cam lobe, broken valve spring, collapsed lifter, bent push rod, etc.
     
  7. billr

    billr wrench Staff Member

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    Your logic about the air going past the rings into the crankcase and then you hearing/feeling it come out the oil-fill port is correct. However, there will always be some such leakage past the rings, the question is whether this is abnormally high. The little change in compression with the "wet" test would suggest that piston rings isn't the only problem. Regardless of whether the problem is rings/piston/cylinders or valves or head gasket, poor compression can only be repaired by removing the head(s). Removing a head, even if you use "free" labor, will mean you are committed to inevitable costs or selling the car as an inop "basket case"; hence my suggestion to think about how far you want to go. I would think that V6 Firebird would be worth $1500 in reasonable (running) condition, $500 as-is. With the "free labor" you could probably do valves on both heads for less than that $1000 delta; but if you have to go into the piston/cylinder area it gets much more iffy. That's the gamble you take if you pull heads for further diagnosis. If you have to take it to a shop for this work, then I think the car is BER (beyond economical repair).

    I don't know for sure, but I believe the engine from an auto application will fit OK; you just need to replace the flex-plate with your flywheel. I don't think GM ever made distinctly different engines (Chrysler did!) for the auto/manual apps.
     
  8. nickb2

    nickb2 Wrench. I help when I can

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  9. nickb2

    nickb2 Wrench. I help when I can

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    Bill and I posted at same time, but essentially, we are both saying the same thing.

    Yeah, I was too lazy to read your post before submitting mine. Billr
     
    Last edited by a moderator: Apr 6, 2017
  10. Chaud

    Chaud Full Member

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    mmmmmmmm
     
  11. Chaud

    Chaud Full Member

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    Billr: you read my mind. No doubt I wanted to find out what is wrong with the engine but most importantly I wanted to know if it is worth to spend time and money on it. You covered all the options with examples . I could not have asked more. Thank you so much for your guidance and help.

    nickb2: I thank you too for your assistance. The information in your write up was very helpful. Thanks again.
    Chaud
     
  12. billr

    billr wrench Staff Member

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    Ha, you say I was helpful? I'll take that as a challenge...

    The "flip side" of common-sense is wondering how much you like this car and would want to keep it, in spite of repair maybe costing more than it is commercially worth. What else would you want, and that would be reliable, for the $500-1000 it will cost to repair this? In Calif. our cars are not generally destroyed by rust and can be kept in operation for nearly forever. Another cheap car may be unreliable or also soon require major repair. Another new car is going to be a big pile of $$$.
     
  13. Chaud

    Chaud Full Member

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    Absolutely Agree. I will do the right thing.
    Thanks.
    Chaud
     
  14. nickb2

    nickb2 Wrench. I help when I can

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    Just as an after thought on this thread. If this was my car, I would be very enthusiastic in rebuilding it as there are not many on the roads in my northern province.

    They are useless in the tundra, but north of montreal, this car would be a head turner as we don't see them anymore. That is where the value would NOT overcome the appeal of keeping these rare cars on the road.

    Down south, maybe you guy's see them as daily drivers. Not the case up here. Since we don't have mandated inspection crap, that firebird would no longer have a v6. :D 350's are a dime a dozen up here.

    Performance wise, this could be a cool sleeper car. As long as the body is pristine, throwing whatever under that hood is a breeze. A 350 bolts right in, and then the fun commences. These pre-obd2 models were a breeze to modify. And to boot, gas mileage is almost the same as that wheezing 3.4l.

    If memory serves right, they used the same trans for both engines. So its win win on all counts.

    I'm just saying, a swap like this is way to easy to even think of putting back in a v6. Same time and energy and tooling. All is need is wiring harness for ECU and such and that's it. Or you could even go carb and be done with all that obd1 stuff.

    So, enough of me being green with envy I don't have a dilemma like yours. I have 5 350's laying around waiting to be put in some suburbans, sierra's etc. The indians up here beat the shyte out of their trucks, so plenty of power-trains here, but the trucks are all bent due to hazard driving and unforeseen trees and what not whilst on the budweiser. :giveup:
     
  15. Chaud

    Chaud Full Member

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    nickb2, after reading your comments I have decided not to part with this car. The car body is perfect and very stylish. Surely it will be head turner on the road. Billr feels the same way as you do. Now the challenge is put the plan into action. Thanks again. Chaud
     

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