Ferrari 412 - Newly Rebuilt Cylinder Heads / No Compression Cylinder #1

Discussion in 'Technical Q&A' started by 360modena2003, Jun 3, 2022.

  1. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,023
    #1 360modena2003, Jun 3, 2022
    Last edited: Jun 3, 2022
    Gentlemen, place your bets!

    Your advice and suggestions are needed.

    I had an engine out "service" done and did the following:

    1. New exhaust valves

    2. New valve guides and seals

    3. All valves were lapped and tested for leakage (by flipping over the heads while off the engine and filling the combustion chamber with gasoline)

    4. New head gaskets, all torqued down to spec and in the correct sequence.

    5. New timing chain, tensioner, pulley bearings, etc.

    Yesterday I ran the first compression check with the compression tester and all cylinders except #1 have between 140 and 150 PSI.

    Cylinder #1 is showing ZERO compression.

    The timing was checked and is spot on.The cylinder walls and pistons were checked as well with an endoscope and no marks or damage is visible.

    The engine had great compression on all cylinders prior to disassembly.

    I will remove the cam cover and further investigate, and will also do a leak down test.

    Either the valves are staying open or not opening at all...could a tappet be failing? Perhaps a rag was left inside the intake port of cylinder #1?

    I am attaching pictures of the 412 engine to give an idea on the intake of the cylinders (they are fed through individual trumpets).

    Any ideas on what it could be and troubleshooting ideas?

    Thanks

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  3. craze

    craze Formula Junior

    Mar 5, 2021
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    Take it back to who did the work
    And if it was you and you cant figure it out sorry to say you shouldnt have tackled this job
     
  4. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,023
    Re-read my post, seems you didn't understand the purpose of my post.



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  5. wrxmike

    wrxmike Moderator
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    Mar 20, 2004
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    A valve not closing fully. Perhaps something fell in ?.
    I'd be removing the spark plug and having a look with an inspection camera, and if nothing obvious, slowly turning the motor over by hand while watching the screen. Good luck
    Could also be your compression tester failed :)
     
  6. Ferrari Tech

    Ferrari Tech Formula Junior

    Mar 5, 2010
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    Wade Williams
    Bring the engine to TDC compression for cylinder #1. Install the compression test hose with out the shrader valve installed and connect shop air. It will quickly tell you where the air is going. Intake or exhaust. Then go from there. Valve clearance to see if something is stuck or bent.

    Does the compression gauge needle move at all when the engine is turning over? I suspect it goes up and doesn't stay and it is a valve seat leak, It really doesn't take much to bleed the air off and result in 100% loss.
    If the needle doesn't move at all and there is no resistance when cranking over, then it is a bigger issue, like a bent valve.
     
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  8. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,023
    As mentioned, I went in with my endoscope cam and saw no visible damage or marks.

    I used the same tester for the other cylinders, it definitely works :)

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  9. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,023
    It shows absolutely ZERO pressure.

    Good idea with TDC and then putting compressed air inside.

    I will then listen in at the exhaust port with the manifold removed, intake port with the cam cover off and in the oil dipstick tube.

    If it holds pressure it means the valves are not opening.

    Will keep you all updated, keep the suggestions coming.

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  10. wmuno

    wmuno Formula Junior
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    I would double check the clearances for the valve shims. I suspect one of them is too large preventing one of the valves from closing completely. Even a bad cylinder will give a compression reading greater than zero.
     
  11. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
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    Mystery uncovered! The intake valve is not sealing completely, clearly visible.

    Most probably a bent valve. The question remains how it happened.

    Head comes off tomorrow.

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  13. Ferrarium

    Ferrarium F1 Rookie
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    Someone put the head valve side down on a bench and the cam lobes had that valve open?
     
  14. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
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    Good suggestion, but in my case the cams went in after the heads were placed on the engine and timing set.

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  15. raemin

    raemin Formula 3

    Jan 16, 2007
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    Remove the intake camshaft (that's the easiest one) and check for leaks. If it fails, just drop the head... The left side is slightly less cumbersome (i am not a mechanic, i can drop it in 16hrs), the right side comes with lots of ancilaries (vacuum pump, steering pump, auto-leveler pump) so it's a bit more work.
     
  16. Ferrarium

    Ferrarium F1 Rookie
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    Well then the valves bumped the piston when timing it. Unless of course she shop is fibbing and they gave it to you that way.
     
  17. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
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    But if the valve made contact with the piston, there should some mark on the face of the piston? The valves are made of carbon steel, and the piston is aluminum, so the piston would also get damaged, no?
     
  18. raemin

    raemin Formula 3

    Jan 16, 2007
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    #15 raemin, Jun 4, 2022
    Last edited: Jun 4, 2022
    No... We bent quite a few when my mechanic had forgotten that my flywheel was rotated 180°. Not a single mark on the pistons.(i have forges pistons, not the borgo though)

    There is so much tension on the timing chain, that you can hardly notice you are bending the valves. After you've made the mistake once, you will recognise the slight additional effort right away.
     
  19. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,023
    Great, thank you.

    Great care was placed in timing the engine before the camshafts were mounted, the flywheel mark and 4 marks on the camshafts were nearly perfect when installed - then they were exactly timed by removing the pins in the camshaft sprocket.

    The question now is if only one was bent. All other cylinders are showing 9.5 BAR+ compression, so I assume they are fine.

    One question on removing the head in place, this is the order of sequence I will be doing, any comments?

    1. Rotate the engine until the master link is right between the two camshaft sprocket gears.

    2. Completely loosen the timing chain tensioner, removing the 6 nuts that hold it against the crankcase as well.

    3. "Open the chain" and place the chain left and right of the two camshaft sprockets (Fig. 53)

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    4. Loosen the cylinder head bolts in reverse tightening sequence (- Fig. 42)

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  20. raemin

    raemin Formula 3

    Jan 16, 2007
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    No need to open the chain. With a loose tensioner you can remove the sprockets from the camshafts.

    When you drop the head do not forget the horizontal bolt hiddent by the alternator mount.

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    In order to remove the head, you ca. Use the head protrusions next to the oil filters: with a big lever you can "pry open the head".
     
  21. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,023
    Thanks for the advice.

    I suspect my heads will come right off, as they were installed last week :)



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  22. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
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  23. Ferrari Tech

    Ferrari Tech Formula Junior

    Mar 5, 2010
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    Wade Williams
    When assembling the engine and installing the cams, number one is at TDC and the cam has both valves open in overlap. The intake is the easiest valve to bend. It is the largest and will be closest to the piston. A small move on the intake cam getting it lined up could cause an issue. I am not saying that is what happened, but it is a possibility. I had a new tech bend an intake valve doing just that.
    If the valve clearance was proper, then it happened at the machine shop as they were assembling the head and they set the clearance on a bent valve.
    Just my thoughts. Get a valve in it and go drive it.
     
  24. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,023
    Thank you, I did not know this. I suspect this is what happened then.

    The question is when mounting the cam, due to the tension of the springs against the camshaft and camshaft caps the, the camshaft as a tendency to rotate (out of time); can this cause bending of the valve? What is the best way to "place" the camshaft do the valves open "on time"?
     
  25. Ferrari Tech

    Ferrari Tech Formula Junior

    Mar 5, 2010
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    Cut a strip of business card and put it under a cam cap. Snug the cap and that will keep the cam from rotating while you get it all lined up.
     
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  26. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,023
    Great, thanks.

    It also occurred to me now: Should I mount, time and "block" (with the card trick) the camshaft while it is off the engine?

    This way I will be sure the valves are "in time" with the engine.
     
  27. Ferrari Tech

    Ferrari Tech Formula Junior

    Mar 5, 2010
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    Wade Williams
    You can lock the cam with the trick as you assemble the heads on the block. I usually don't put the cams in until the after heads are on though.
     
  28. 360modena2003

    360modena2003 Formula 3

    Jul 11, 2009
    2,023
    The risk I see, which is possibly what happened, is that once the head is assembled on the block, when one starts clamping down the cam, it will invariably rotate in any direction, depending where the cam lobe is pressing against the tappets, and this could push the valve (out of the time) against the piston...
     

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