Let’s Tune This Engine

Discussion in 'Cams, Heads and Valve Trains' started by DorianL, Feb 22, 2021.

  1. DorianL

    DorianL solid fixture here in the forum Staff Member

    My issue is:



    I’d like to see a much more stable needle.

    Before the cam swap I was rock steady at 17-19 inches.

    Now I’m getting a rapid vibration between 20-16 inches of vacuum. My idle doesn’t sound perfect either.

    Tomorrow I’ll once again use my temp gun. Last time I found a broken spark plug and when I replaced it it dramatically improved performance.

    I tried to set valve lash hot but it’s so noisy it’s difficult to hear the clacking.

    I may well do the lash over
    Intake closing -> adjust exhaust valve
    Exhaust opening -> adjust intake valve
    Plus one full turn as per Comp Cams instructions.

    When I film in slow motion the needle drop is extremely regular.

    The carb being EFI there’s not much to do there. Just the ignition.
     
    Last edited: Feb 22, 2021
  2. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    Id sure start with getting the valve lash correct, even a hydraulic roller cam should be rather quiet at idle not noisy , with properly adjusted valves
     
  3. Loves302Chevy

    Loves302Chevy "One test is worth a thousand expert opinions."

    Do it while running at idle. Use cardboard to keep the oil splash from hitting the exhaust.
    You can isolate sounds like that by shoving a length of vacuum tubing in your ear and using it as a stethoscope.
    And only go 1/2 turn extra after the clatter stops.
     
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  4. DorianL

    DorianL solid fixture here in the forum Staff Member

    I need to find my $@#% stethoscope back. Grrr

    interestingly there was a lot of RTV on the two bolts I took out.
     
  5. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    I really REALLY WISH you and I and many of the guys on this web site,
    were locally located (in the same neighborhood)
    there are just so many things I know and probably take for granted, and skills and tools that I'm sure
    we could use to teach or do to help each other in areas like this build and tuning,
    that are so easily done (HAND'S ON)
    that are otherwise hard to demonstrate/ easily convey or teach.
     
    Unforgiven likes this.
  6. DorianL

    DorianL solid fixture here in the forum Staff Member

    Very frustrating here as well as it probably is something very simple. I’ll try setting valve lash hot. Will also use temp gun on all exhaust pipes of the header to make sure all cylinders are firing properly.

    In the meantime I need to find back my automotive stethoscope. Super useful.
     
  7. DorianL

    DorianL solid fixture here in the forum Staff Member

    Figures. Found it. It was only exactly where it was supposed to be but I didn’t see it the first three times I looked. Ah the joys of aging :rolleyes:
     
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  8. Mark Bradley

    Mark Bradley Da guy in Newbury

    A couple things to cover....
    1: what type of lifters. Comp Cam Short travel rollers only need 1/8-1/4 turn after the lash is out and what you are seeing is classic... I have done it. I have attached Comp Cam procedure and it works great.
    2: As for the EFI... feel free to ping me at SoCalEFI.com and we can work it out then share the results back here if you wish.
    Basic questions if you don’t mind...
    What are the old cam specs?
    What are the new cam specs?
    Compression ratio?
    Idle RPM?
    Ignition timing at idle?
     

    Attached Files:

    Last edited: Feb 23, 2021
  9. Mark Bradley

    Mark Bradley Da guy in Newbury

    AS A TEST...
    If the valves are too tight you can loose lash the valves and while they will be noisy they will likely improve the idle enough to prove they were too tight.
     
  10. DorianL

    DorianL solid fixture here in the forum Staff Member

    Interesting.

    I’m using High Energy Comp Cam lifters.
    https://www.summitracing.com/parts/CCA-853-16

    I can’t find it back, but I seem to recall the paper that came with them called for one full turn. I got chicken and kept it to 1/2.

    Thanks for the EFI help. I could use that. Start up is not as smooth as it should be.

    The old cam is a mystery. A custom grind.

    The new cam is
    Hydraulic roller tappet
    Basic Operating RPM Range:1,600-5,400
    Duration at 050 inch Lift:218 int./224 exh.
    Valve Lift with Factory Rocker Arm Ratio:0.495 int./0.502 exh. (I have 1.55 rockers)
    Lobe Separation (degrees):110

    Compression is allegedly 10:1

    The timing at idle (with vacuum advance) is 22 degrees.
     
  11. DorianL

    DorianL solid fixture here in the forum Staff Member

    Would you guys set the lash running hot or static cold ?
     
  12. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    Id set it hot /running and just 1/2 turn in ,max past where its stops clicking as you tighten the lash out of the hydraulic lifter,
    just back off the rocker until it clicks at idle then slowly tighten until the click stops then add a 1/2 turn max, not all that high tech, but its worked flawlessly for decades
     
    DorianL likes this.
  13. DorianL

    DorianL solid fixture here in the forum Staff Member

    This is so frustrating.

    I can hear a clacking sound at idle. It sounds like a loose rocker. It’s quite loud. It’s seems to be a single one.

    A slow motion recording of the vacuum gauge reveals a very regular oscillation between 21-18 inches.

    I tried setting the valve lash hot but it’s extremely difficult to hear exactly when the clacking starts and stops.

    With the stethoscope I listened to exhaust headers. The clacking seems to be louder on the driver’s side.

    I listened to each of the rocker studs and they all sound the same. You can hear a loud clacking on the top of each rocker stud bolt. I’ll check if I hear that on the other side.

    So frustrating.

    Temp a bit low on exhaust 1.
     
  14. DorianL

    DorianL solid fixture here in the forum Staff Member

    At this point I’m worried about a lifter failure. :rolleyes:
     
  15. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    it might be a clearance issue like,
    the rocker slot binding on the rocker stud momentarily
    or the spring binding at full lift,
    rocker under side contacting retainer,
    retainer touching valve seal,
    rocker lock nuts contacting inside of rocker,
    have you checked piston to valve clearance!
    pushrod rubbing on guide plate or slot, in heads, etc.
    you should not hear metallic clicking if theres zero clearance issues,
    once valves are properly adjusted
     
    Last edited: Feb 24, 2021
    Mark Bradley, Unforgiven and DorianL like this.
  16. DorianL

    DorianL solid fixture here in the forum Staff Member

    Hmm. Good points. I hadn’t thought of any of that. I wonder if the pushrods are contacting the guide plates.
     
  17. DorianL

    DorianL solid fixture here in the forum Staff Member

    Well, full disclosure, I banana-ed a pushrod. I forgot to tighten the lock nuts and presumably they came loose and boom ! Rookie mistake.

    New pushrods on order. Replacing all of them, just to be sure.
     
  18. rlphvac

    rlphvac reliable source of info

    A rookie mistake but one you will never make again and as far as a lesson learned this one wasn't an expensive one as they go
     
    Unforgiven likes this.
  19. busterrm

    busterrm solid fixture here in the forum

    I would get the ignition lined out, I have a sneaking feeling there's a cylinder misfiring. Does it have new wires and plugs? Just to make sure its firing on all cylinders.
     
    DorianL likes this.
  20. DorianL

    DorianL solid fixture here in the forum Staff Member

    I would agree with you there. I have a hunch too. Not new plugs but they looked good. Wires are a couple of years old.
     

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