The Force Awakens...

Discussion in 'corvette related misc.' started by DorianL, Nov 22, 2017.

  1. DorianL

    DorianL solid fixture here in the forum Staff Member

    Did a test drive, at higher RPM it does seem to be missfiring. Anything above 3000 rpm feels uncomfortable.
     
  2. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    the the tall cast valve covers I fabricated/modified for valve adjustment is taller and has a smaller open area,
    but yes the basic concept of having a valve cover modified to adjust valves at idle works very effectively,
    I bought a used set like these to modify and drilled 8 -2 1/8" diameter round holes centered on the rocker studs (yes the holes overlap)

    [​IMG]
    [​IMG]
    http://garage.grumpysperformance.com/index.php?threads/correctly-adjusting-valves.196/
     
    Last edited: Jan 6, 2018
  3. Indycars

    Indycars Administrator Staff Member

    Are you using the push button start still or have you removed it?

    Any chance there are still some wires associated with the push button or key start that need further inspection?
     
  4. DorianL

    DorianL solid fixture here in the forum Staff Member

    Yes. I was very pleased with the results of setting the valve lash this way.

    The engine seems to sag in power at 2500 plus rpm. It vibrates as well and shudders.

    On the timing light idle seems fine and up to 2200 rpm the mark looks good. Pushing above 2500 rpm and you can feel the engine doesn’t like it. The timing mark comes and goes and sometimes seems to pop up quite retarded.

    This is an HEI but not GM. Some aftermarket thing with a mechanical tach drive. It looks about new. Cap and rotor look pristine. As do the cables.

    I’m going to:
    - check the gaps
    - check the resistance on the HT leads (as the Brits call them)
    - give direct full battery to the ignition instead of running through the firewall connector. I have a small length (a few inches) of the original wire there... but that was originally for points... I’m wondering if there is some resistance there...

    Beyond that, I suppose it’s the coil or the module.
     
  5. DorianL

    DorianL solid fixture here in the forum Staff Member

    I rewirded it to a free IGN spade on the fuse panel. I do here the solenoid snapping every time. Nonetheless, you are right, I’ll try giving an alternate source to see if that changes anything
     
  6. DorianL

    DorianL solid fixture here in the forum Staff Member

    I tried to go back to the original key ignition but there’s something wrong with the column. On my to do list: rebuild the steering column.
     
  7. Indycars

    Indycars Administrator Staff Member

    Does it snaps once or clicks over and over until the key is released?

    If the solenoid clicks every time, then the push button must be good. What's the voltage at the
    starter with the button pushed and the solenoid energized ?
     
  8. DorianL

    DorianL solid fixture here in the forum Staff Member

    It clicks every time I push the button.

    I’ll check the voltage tomorrow morning;-)
     
  9. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    If you suspect a worn cam lobe, checking the cams lobe lift with a dial indicator on the valve spring retainer vs the other lobes would certainly provide useful related info.
    knowing vs guessing helps in making decisions wisely
    http://www.summitracing.com/parts/pro-66830/overview/
    [​IMG]


    https://www.harborfreight.com/multipositional-magnetic-base-with-fine-adjustment-5645.html

    [​IMG]
    https://www.harborfreight.com/catalogsearch/result/index/?dir=asc&order=EAScore,f,EAFeatured+Weight,f,Sale+Rank,f&q=indicator+stand
     
  10. DorianL

    DorianL solid fixture here in the forum Staff Member

    I replaced the wire leading to the ignition with a 12 gauge from the horn relay; fused.

    I also closed all my gaps from 0.050 to 0.040.

    That seems to have dramatically cleaned up the ignition.

    I’ll use the original wire to fire a relay.
     
  11. DorianL

    DorianL solid fixture here in the forum Staff Member

    Time for a little update...

    I put a relay on both the line to the coil/distributor and to the starter solenoid and that seems to have cleared things up dramatically. The starter no longer seems to hang and spins nice and fast. No more detectable high RPM misses.

    I took the corvette out for a series of test drives and, it seems that I have a sticky thermostat: temp spikes and slow or erratic behavior. I'll replace that within the next few days taking care to drill some holes in the thermostat flange.

    Soon I will start looking into tuning what I have... which isn't much: 882 heads, headers, who-knows-what cam, Torker intake and 750CFM Performer carb. I have good compression and oil pressure; I am happy about that.

    The idle quality is good - I'll check this weekend how many inches of vacuum I am getting. But from experience, I'd say at least 15. I don't know if it is the cam or the burble of the twin Flowmasters that give the car a feeling of vibration at 2500-3000 rpm. The sound might be misleading me. It almost feels like the rotating assembly was not properly balanced. I'll need to focus my senses the next time I take this for a drive (after I swap the thermostat.)

    I rebuilt the carb; it has the original Performer tuning on it. The ignition curve, I still have to check. I am going to double-check TDC. (Anyone have a tutorial on converting a spark plug into a piston stop?)

    There is significant bogging when I get on the gas. Peak torque feels around 2800-3000 rpm. Beyond that is seems to run out of steam.

    Once I get the basics done, I will take it down to a dyno. I also have a dual wideband O2 sensor... I just need to get a couple of bungs welded in. We shall see what I can find out there.

    I also have to remember that I have at least one cam lobe that is worn... that might be a factor; number 8 intake barely rocked over when setting lash.
     
  12. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    Last edited: Jan 17, 2018
  13. DorianL

    DorianL solid fixture here in the forum Staff Member

    Thanks - that is the advice I needed to hear.
     
    Last edited by a moderator: Jan 17, 2018
  14. DorianL

    DorianL solid fixture here in the forum Staff Member

    Just a shame considering the good oil pressure and compression...
     
  15. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    its only a mater of time before that metallic trash causes other moving component wear issues
    this is one reason changing oil filters, rather frequently (at least every 7-8K miles)
    (IDEALLY the long versions with extra surface area)
    and having previously installed several high temp magnets in an engine, you build,
    is rather critical too preventing similar damage in any future engine builds

    http://garage.grumpysperformance.com/index.php?threads/metallic-debris-in-filter.12364/#post-61283

    http://garage.grumpysperformance.co...filters-wix-vs-royal-purple.12988/#post-67560
     
  16. Loves302Chevy

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

    Simple answer. Cut or grind the ground electrode off. Smash the porcelain off and out. Determine what thread the ID will accept for the center bolt.
    Tap the new threads. Install bolt. Done.
     
    DorianL likes this.
  17. Indycars

    Indycars Administrator Staff Member

  18. DorianL

    DorianL solid fixture here in the forum Staff Member

    Thanks Gents...

    Man, Rick !!! You pics are always so stunning. Could almost eat lunch off of them or perform surgery with them and still not risk infection...
     
  19. DorianL

    DorianL solid fixture here in the forum Staff Member

    Hmmmm, I have a nagging suspicion this might be a bent pushrod. The engine seems to be in too reasonable condition for it to be something so catastrophic.

    First I'll put my vacuum gauge on this, then I'll yank the push rod and check it against a straight edge.
     
  20. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    you also might want to swap out those older stock stamped rocker arms for new ones when you do a compression test, they may be excessively worn and they don,t cost much to replace.
    in fact swapping to a set of the stamped 1.6:1 ratio stamped rockers is a cheap and usually effective upgrade, if you keep it simple and check clearances carefully you could rather easily gain 10-12 hp from the increased valve lift and usually more consistent ratio, quality control on the parts dimensions.(stock stamped chevy rockers are supposed to be 1.5:1 ratio but they rather frequently actually measure closer to 1.4:1-1.44:1
    https://www.summitracing.com/parts/sum-g6801/overview/make/chevrolet
    (BE DAMN SURE you check clearances , especially on the push-rods to cylinder head guide slots)


    http://garage.grumpysperformance.co...swap-in-1-6-1-ratio-rockers.10671/#post-46039

    http://garage.grumpysperformance.co...rocker-ratios-and-the-effects.126/#post-37621

    http://garage.grumpysperformance.co...-rocker-ratio-help-your-combo.2632/#post-6790
     
    Last edited: Jan 18, 2018

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