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308 turbo leak down test

Discussion in 'Technical Q&A' started by 4returbo, Nov 17, 2004.

  1. 4returbo

    4returbo Karting

    Oct 14, 2003
    60
    Indiana
    Full Name:
    Rick Oliver
    I have the ferrari turbo test results. FAILED! Big time. My question is; did I do it right? My assistant and I replaced a coolant leak under the intake plenum. Started up the car and got the usual smoke and oil. After a while the car heated up and was running very well. (much less smoke and oil and steady idle, if you read past post by 4returbo Big improvement). With the car heated up we started the test.... Wait can't find the only socket that will get the plugs out. After a trip to Sears (engine not cold not hot) all plugs are out we start the test. In a nut shell he turned the engine while I watched the gage. 100% leak... he keeps turning 80% keeps turning... 40% ... 15% ... 12% ... 12% ... 30%... 80%.. get the picture? We did this until the min percent was reached and held. My results.... Sad to say.

    14% 15% 29% 14%

    13% 37% 32% 38%

    Would the results be better if the engine was warmer?

    Are the results valid with the method we used?

    Needless to say I am going to perform another one and listen for air leaks in the exhaust, intake and valve covers.
     
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  3. maurice70

    maurice70 F1 Rookie

    Jan 25, 2004
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    Rick could you please explain how you did the leak down test?Thanks.
     
  4. speedmoore

    speedmoore Formula 3
    Professional Ferrari Technician BANNED

    Apr 15, 2003
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    Never should you do the test this way....you will get false readings.

    Put all the spark plugs back in and run it a little. Then let it sit. Doing it warm will make it better if it's bad. But I prefer doing cold at our shop.

    BIG NOTE HERE: Bring Cyl. no 1 to TDC of compression stroke (both valves closed) then remove the spark plug. Do this by hand with a 1/2 drive ratchet and a 36mm socket. Use the timing marks on the flywheel along with the ignition rotor. If you remove the plug beforehand, bits of carbon can be disturbed and get between the valve and seat and you will get a false reading. Do this for every cylinder. You will have to remove the distributor caps to see which cyl. is on compression (the rotor will be pointing towards that wires connection point).

    BTW, this is also necessary when adjusting valves (leave spark plugs in place).


    If you still get 80%, chances are you have a broken piston ring or a bad seating valve.

    Listen in the exhaust pipe for leakage past exhaust valve, listen inside the throttle body for the intake valve, listen in the dipstick tube or breather or open up the oil filler cap and listen for leakage past the rings/pistons.

    A blown head gasket can also give bubbles into the coolant tank or oil bubbles at the cylinder head to block interface.

    All you are doing with a leak down is forcing air into the combustion chamber that is "supposed" to be sealed on a fresh motor at TDC of compression stroke. Anything under 10% is good on a 4 valve motor. Above that, is when you need to start paying attention to where the air rushing out sound is and why.

    David
     
  5. 4returbo

    4returbo Karting

    Oct 14, 2003
    60
    Indiana
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    Rick Oliver
    1) Jacked up the car and removed rear passenger wheel to access the crank.

    2) Removed all spark plugs

    3) Connected gage and watched the needel as someone turned the engine by hand. When the needle was indicating 100% you could hear hissing in the exhaust. Meaning to us that the exhaust valve was open. As we turned the engine the cyl. compressed and valves closed the needle would go down then stop at a % as low as 13 and high as 38. (this is what we took as our reading).
     
  6. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
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    Rick~

    Have you checked your valve clearances and made sure you have clearance? If you have a tight valve you could have compression escaping that would lower your readings. And as posted earlier, listen at exhaust, intake, and oil cap to see "where" its escaping. Accurate readings should always be taken on a hot engine.

    What you want to do is "hold" the piston steady at top dead center and double check your leak tester to make sure your primary guage is at 100 psi. or you can use 80 as well, but you have to recalculate percentage We used 80 on aircraft because the pistons are so large in diameter, and you had to turn the engine with the propellor and hold onto it as pressure was applied.

    However, one thing we did on aircraft that is normally not done on cars, involved walking the prop back and forth over top dead with pressure applied to get the rings to "snap" into place. You could physically hear them make a snapping sound as they locked in, and see the guage pressure jump higher, as well as feel a sudden increase in effort to try holding back the prop. Sometimes it took three or four swings back and forth to get them to snap. So just hooking it up at TDC and applying pressure may not be enough to get an accurate reading. But on a large bore engine you would be amazed at the torque on that prop trying to keep it from whipping away from you, lol
     
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  8. 4returbo

    4returbo Karting

    Oct 14, 2003
    60
    Indiana
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    Rick Oliver
    TDC still eludes me. Can someone give me a lesson in "How to find Cyl. No 1 TDC for dummies"? Illustrations or pics would be helpfull. I searched this topic in found nothing definitive on the matter. The best idea I heard was a sick in the plug hole and when it stops going up you're TDC. Anyone offer something better?
     
  9. bpu699

    bpu699 F1 World Champ
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    Dec 9, 2003
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    You can find TDC visually through the plug hole - its when the cylinder is closest to the head...of course a indicator gauge is even better (200$). When the cylinder is at the top, you are either in the compression cycle (where you do your reading), or the exhaust cycle (with zero pressure)...

    The method you were using sounds more like a compression check than a leakdown - were you trying to do the former? In a compression check you attach the reader and flip the motor through a couple of cycles...

    If I'm explaining the obvious, let me know. I'm just chiming in the limited knowledge I have.
     
  10. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
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    TDC on #1 cyl is where the piston is up all the way, and your crankshaft mark is centered, but also, at the point in revolutions where it would be firing, with both valves closed. If you have your cam covers off and your plugs out, you can turn the engine in the normal direction of rotation, and watch the cam lobes open and close the valves for number one cylinder and watch your flywheel. If you are VERY CAREFUL, you can use a long thin rod or slim screwdriver down the plug hole as you SLOWLY turn the engine, and being careful to KEEP IT FROM JAMMING watch it move up and down as you rotate the engine. Remember, you have to turn TWO COMPLETE REVOLUTIONS to complete all four cylces: intake-compression -BDC power -TDC exhaust, in 180 degree intervals.
    You test your leakdown at TDC with both valves closed (TDC on compression stroke). With your distributor cap off, your rotor will be pointing at number one at the point you want to test. You can follow the rotor around as you turn the engine and roughly find TDC on compression for the other cylinders, which will follow the firing order in 90 degree intervals of crankshaft rotation. Remember, the camshafts only turn at half the speed (two turns of crankshaft for one turn of cam) on the crank.
     
  11. mk e

    mk e F1 World Champ

    Oct 31, 2003
    11,813
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    What I do for TCD on a leak-down is just plug the plug and drop about a 12" long piece of alum welding rod (tig rod no flux) in the hole. Then turn the engine until it stops coming out of the hole. Your there plenty close enough for a leak-down test. Then put it in gear, parking brake on to keep it from trning and run the test. But, it might be the wrong revolution (valves open), if I get a 0, I move the gage to the mate cylinder (1-4,2-3, 5-8, 6-7), it will be at the top of compression. On the 308 I find the number are ramdom and low when the engine is cold. I do it with the engine pretty warm and I get very repeatable.
     
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  13. Artvonne

    Artvonne F1 Veteran

    Oct 29, 2004
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    Once again, I have to reiterate something learned from aircraft I posted earlier. And aircraft have pistons and rings the same as cars do. We had to swing the propellor back and forth, basically running the piston back and forth over TDC to get the rings to "snap" and lock up to hold full pressure. You could not only "hear" it, but you could "feel it", and "see" it on a guage.

    Not only that, but some engines were significantly in the last 1/4" to 1/2" at the top of the cylinder, and if your leaking at TDC, you can bring the piston down under pressure and see if the pressure comes up, indicating worn cylinder bores
     
  14. Martin Meade

    Martin Meade Karting
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    Oct 25, 2004
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    Good call krowbar. When the piston is at TDC on compression, that is when cylinder pressure is the highest. This pressure goes past the top of the ring groove and presses on the backside of the top compression ring, increasing ring seal. This causes leakdown to be more at TDC than 1/2" down in the bore on a worn out engine. This is also what causes bore taper and a ridge at the top of the bore. Blowby is increased as well.

    Good luck

    Martin
     
  15. Artvonne

    Artvonne F1 Veteran

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    Actually, what I was trying to say, and one word kinda messed it up, is that yes, max compression would be at TDC, but sometimes the cylinder wears very significantly in the very last (top) 1/4"-1/2" of the cylinder bore. Walking the piston up and down a short ways eaither side of TDC can sometimes show an increase in leakage right at TDC but better sealing just below it, which indicates the cylinder is becoming significantly worn.
     
  16. Verell

    Verell F1 Veteran
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    May 5, 2001
    7,000
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    TDC:
    The 308/328s have flywheel marks that make it easy to get half the cylinders on TDC. There's the letters PM 1-4 associated with a vertical line, and also PM5-8. Unfortunately, TDC for cylinders 2-3 & 6-7 are 180 degrees away from the marks. Next time I do a clutch job, I'm going to add marks for them to my flywheel with steel stamps. May also add marks for valve timing while I'm at it.
     
  17. brian.s

    brian.s F1 Rookie
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    Nov 3, 2003
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    You only need to find #1 TDC, take that reading, rotate the crank 90deg +/_ and follow the firing order. Should take less than an hour. For what you are trying to learn about your engine it is not critical to the big picture to do the back and forth business. You are looking for the big discrepancy, any cylinder under 12% can be ignored for now.

    Brian
    www.autocarsports.com
     
  18. F40Lover

    F40Lover Karting

    Mar 28, 2004
    203
    This goes to show you that compression isn't everything. A leak down test will reveal many things. You can also listen to the tail pipe and see if you hear or feel airflow, this means exhaust valves are leaking and if the same is true for injectors this means intakes are leaking. Can be the valve seals or seats. To determine wich requires a teardown. Good thread.
     
  19. Artvonne

    Artvonne F1 Veteran

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    Well, as long as your holding the engine from turning with a breaker bar, as long as your holding it near TDC anyway, why not rotate it back and forth to get a full analyses? Hurry up jobs never are the way to go.
     
  20. brian.s

    brian.s F1 Rookie
    Professional Ferrari Technician

    Nov 3, 2003
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    30 years of building race engines, working on Porsche and Ferrari. Never done a hurry up job, just efficient FWIW.
    Finished Indy 500 5th place with an engine with 1 cylinder 18% before the start. Read same after. But what do I know?
     
  21. Artvonne

    Artvonne F1 Veteran

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    I don't know what you know. But this guy needs to determine exactly what he is up against and if hes taking the time to learn his car, and his engine, and learning how to do a leakdown test correctly, then it should be done correctly so he knows how to do it. If he has drastically worn cylinders he needs to know now, as perhaps he would be better off at that point just finding a good used engine than doing an entire rebuild with new cylinders instead of bothering to tear his engine apart. I just see no need to cut corners.
    Now on your Indy car, are you talking 18% loss? My 308 which is apart right now, and which had no loss at valves on any cylinders, had about that same amount of loss on cylinder number 7. The piston is burned down to the top compression ring over a quarter of the way around.
     
  22. 4returbo

    4returbo Karting

    Oct 14, 2003
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    Indiana
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    Rick Oliver
    Thanks to all. Lots of good information on this thread. I can't wait to try out everything suggested. Look forward to a new thread started around December 17-29, I have time off from work and will be paying some close attention to my car. Thanks again to ALL! I too love this community of Ferrari fanatics "like me".
     

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