Register now to get rid of these ads!

Technical do a isky cam make low vacuum ?

Discussion in 'The Hokey Ass Message Board' started by oldsfrench, May 31, 2019.

  1. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    Hello hambers
    New rebuilt 324 olds. Rebuilt carb. Rebuilt distributor. New spark plugs
    New fuel pump. ..New points and condenser. New coil. .
    Here we go
    Engine runs fine, idle is steady
    800 in neutral, 600 in drive.
    Compression test is all cylinders are
    125 /130.
    But i have low vacuum.
    Vacuum gauge says 8 at 600 in drive
    And 10 in neutral all vacuum ports plugged.
    This engine has à isky cam And i want to ask you if a isky cam make low vacuum ?
    Engine runs fine but i have not enough
    Vacuum to make the power break ..
    (Sorry for poor english. i am french )
    Thanks a lot for your answer. .
     
    42merc and Deuces like this.
  2. FrozenMerc
    Joined: Sep 4, 2009
    Posts: 3,093

    FrozenMerc
    Member

    Without knowing the cam specs we can't tell you. It is absolutely possible that your cam does not allow much vacuum to be built, or that you have something else wrong. We need to know the specs, as Isky cams come in a wide variety of profiles. Also, what units are you measuring vacuum in? I am assuming in-Hg, but being from the other side of the pond, there are lots of other choices.
     
    lothiandon1940 likes this.
  3. plym_46
    Joined: Sep 8, 2005
    Posts: 4,018

    plym_46
    Member
    from central NY

  4. jaw22w
    Joined: Mar 2, 2013
    Posts: 1,671

    jaw22w
    Member
    from Indiana

    Yes, it is entirely possible to only have 8" of vacuum at idle. This is a common problem with big cams and power brakes. The answer is a vacuum reservoir and/or vacuum pump. Or milder cam.
     
    lothiandon1940 likes this.

  5. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    Tanks a lot for your Quick answer guys..
    Isky cam is 270 duration and 450 lift
     
  6. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    Vacuum gauge is in -hg.
    I set ignition timing 9 degrés at idle 600
    Dwell 29. valves lash 0.018 mixture screws are 2 turns
     
  7. Russco
    Joined: Nov 27, 2005
    Posts: 4,327

    Russco
    Member
    from Central IL

    Try advancing the timing a little more and see if that helps.
     
    deathrowdave likes this.
  8. Deuces
    Joined: Nov 3, 2009
    Posts: 23,754

    Deuces

    Did you adjust the 2 screws using the vacuum gauge for the highest reading?????
     
  9. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    I set timing at 9 because that's where the engine is fine, if i put more advance idle is not good.

    Yes deuces i read the vacuum gauge
    To set the mixture screws at the highest reading it was about 2 turns
     
    Deuces likes this.
  10. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    thanks for the link ..
    i found a mechanical vacuum pump in my shop ...
    will try to instal this afternoon..
    20190601_102647.jpg

    also i thought i might drill a larger hole in the base plate to enlarge the vacuum output..
    is this a good idea ?
    the base plate in the pic is not the one on my engine , it's an old base plate for example
    the two holes where i put the wood small piece...
    20190601_103541.jpg
     
  11. OLDSMAN
    Joined: Jul 20, 2006
    Posts: 2,422

    OLDSMAN
    BANNED

    The overlap in the cam is what kills vacuum, that duration doesn’t seem too wild.
     
    lothiandon1940 likes this.
  12. deathrowdave
    Joined: May 27, 2014
    Posts: 3,519

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    Did you adjust timing with vacuum advance connected or disconnected ? It seems to me your issue is being caused by late ignition timing , which could very well have been caused by adjusting your timing with the advance connected to a vacuum source . Your cam specs do seem to be large enough to cause the issue you are dealing with .
     
    lake_harley likes this.
  13. Ericnova72
    Joined: May 1, 2007
    Posts: 595

    Ericnova72
    Member
    from Michigan

    Drilling the baseplate passage larger, like you indicated in the photo, won't change a thing....vacuum would be the same if the hole was 1/8" or 2" in diameter.

    Camshaft part #, or cam card full specifications would help out a lot....lobe separation, intake lobe centerline, and the Duration @.050" lifter rise opening and closing points for intake and exhaust so we can determine degrees of overlap and the intake valve closing point in relation to crank stroke and piston location in the bore.
     
    Deuces likes this.
  14. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    I set timing advance with not connected vacuum port.
    All vacuum ports were plugged.
    I set first timing this way :
    Put #1 cylinder at tdc. Plug a Light on ingnition coil . turn distributor since the light shine.
    Fire the engine, and turn the distributor again left and right so the engine runs better.
     
  15. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

     
  16. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    Unfortunately i dont know a lot about this cam. .i purchased this engine from a good guy here in hamb forum board.
    (@paul55 i know you made a good job on this engine i don't want to offense you )
    All i have is this pic
     
  17. Don't drill the carb baseplate, connect your power brake booster directly to the intake manifold. While that won't improve the inches of vacuum, it will help with volume.

    As everyone has pointed out, cam specs can have a huge affect on manifold vacuum. If that's 270 degrees @ .050" lift, that's pretty lumpy.
     
  18. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    the only one pic i have :
    DSC02965.JPG
     
  19. PackardV8
    Joined: Jun 7, 2007
    Posts: 1,170

    PackardV8
    Member

    Your problem is not too much cam but not enough compression. If the cranking compression was 165 - 185 or better, the idle and vacuum would be much improved.

    Since you can't easily change the compression, try loosening the valve clearance until it becomes noisy at idle and see if the idle vacuum improves.

    jack vines
     
    Truck64, Deuces and olscrounger like this.
  20. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,217

    2OLD2FAST
    Member
    from illinois

    You say if you put more timing in it , idle is " no good" . Do you mean it gets rough ? I think possibly your expecting a smooth , low room idle that the cam is just not capable of .You can try backing off the lash adjustment as has been mentioned , increase both the timing and idle speed to see what that does . Your converter may be too tight for that cam also ...initial timing for a 270° cam I would guess would be 12-16° @ 8-900 rpm ....
     
    Last edited: Jun 1, 2019
  21. For all its worth, Isky catalog recommends .020 valve lash hot..
     
  22. deathrowdave
    Joined: May 27, 2014
    Posts: 3,519

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    So you have no idea the number of advance you have timing set at ? As it has been stated you will never get a smooth idle . But I. Sure vacuum will get better as you advance the timing . If you set timing as you suggested , I would allow the engine to run until it’s operating temp. And raise the timing until it kicks back while cranking , then slowly back it off until it spins freely . I forgot to ask how did you adjust your valves ?
     
  23. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    before i set the valves lash about 0.018 ,it was about 0.025 but engine was very noisy....
    but vacuum was very low too...

    i set the valves lash this way :
    when intake valve 1 is fully open , i set intake valve 6
    when exhaust valve 3 is fully open , i set exhaust valve 2
    when intake valve 8 is fully open , i set intake valve 5
    when exhaust valve 6 is fully open , i set exhaust valve 1
    when intake valve 7 is fully open , i set intake valve 4
    when exhaust valve 5 is fully open , i set exhaust valve 8
    when intake valve 3 is fully open , i set intake valve 2
    when exhaust valve 4 is fully open , i set exhaust valve 7
    when intake valve 6 is fully open , i set intake valve 1
    when exhaust valve 2 is fully open , i set exhaust valve 3
    when intake valve 5 is fully open , i set intake valve 8
    when exhaust valve 1 is fully open , i set exhaust valve 6
    when intake valve 4 is fully open , i set intake valve 7
    when exhaust valve 8 is fully open , i set exhaust valve 5
    when intake valve 2 is fully open , i set intake valve 3
    when exhaust valve 7 is fully open , i set exhaust valve 4
     
  24. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    yes : if i put more timing ,i can't set idle before 900 , idle is not steady and want to die....
    the trans is a jetaway, has no converter..
    i want to set idle about 650/700 because if i set higher idle , when in drive , the car wants to run without i push the throttle pedal...
    i'll re-set valves lash at 0.020 ,re-chek compression , will set initial timing about 12---16 ...
    and keep you informed ,
     
  25. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    i made a big mistake with the compression reading gauge ,
    here in europe , scale is "bar" so the the gauge said 12.5 /13 bars witch is good
    on the green zone ( 185/190 for you ... )
    sorry for this....
    20190603_095940.jpg
     
  26. karl share
    Joined: Nov 5, 2015
    Posts: 115

    karl share
    Member

    My 57 Olds has a factory fitted vacuum tank fitted in the passenger side inner guard, do you have one??
     
  27. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    yes karl , mine has a vacuum tank too. and i cheked it wasn't leaking...
    this car has factory power break and power steering.
    power break were fine with the original tired engine...
     
    Last edited: Jun 3, 2019
  28. oldsfrench
    Joined: Jan 26, 2018
    Posts: 243

    oldsfrench
    Member
    from France

    i made new settings this morning ,
    set the valves lash at 0.020...
    fire the engine , wait until it is hot , set idle at 850 rpm with vacuum gauge connected , and turn the distributor to read the max vacuum
    it was at 18..
    take the timing light and read advance is 32 degrees....:cool:
    turn the distributor back to 20 degrees , and now vacuum is 14...
    i think it is enough to make the power break .
    noooooooo... i still have a hard pedal...
    i now think the problem is the power break vacuum is perhaps leaking...
    will make leak test this afternoon, engine is now hot, and i don't want to burn my hands....
    do you guys think i cant left initial timing at 32 degrees ?
     
  29. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,217

    2OLD2FAST
    Member
    from illinois

    I'm no olds expert , maybe someone can tell you how much TOTAL( initial plus mechanical less vacuum) advance the olds will take without detonation , on a Chev it's usually under 40° ......just more to learn ....
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.