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Technical SBC non-stock tune up - does this seem right?

Discussion in 'The Hokey Ass Message Board' started by David Gersic, Apr 22, 2019.

  1. tb33anda3rd
    Joined: Oct 8, 2010
    Posts: 14,483

    tb33anda3rd
    ALLIANCE MEMBER
    1. Connecticut HAMB'ers

    you did it wrong. use the clips and a cut open rocker cover or cardboard and loosen them slowly while it is running. ten thousands shouldn't cause a problem. friend of mine had a "street/strip" car back in the day, huge cam that he ran "loose" back and forth to the track, then do his adjustment before the race. ........like having two different motors.
     
  2. BadgeZ28
    Joined: Oct 28, 2009
    Posts: 964

    BadgeZ28
    Member
    from Oregon

    Boy, let me reinforce some of the suggestions. 1. the cam has too much duration. Your setup needs what is called a RV cam. Somewhere around 268 duration. Stock valve springs have a limit on how much lift you can run with them.
    The stock converter might be fine with a mild camshaft.
    If you do nothing else, find a adjustable timing light and determine total advance. You can also buy a adhesive tape with 360 degrees of timing marked on it. Measure the diameter of the balancer and get the right diameter tape. Place 0 at the timing line cut into the balancer. Apply clockwise. I would think 33 degrees total would be a good target.
     
  3. Not really, pull a valve cover
    A magnet dial indicator and a good degree calibration on the balancer should be enough to see if it’s in the ball park. Aka not way off.

    Do you have stock ratio rockers?

    Are the valve springs matched to that cam or are they stock as well?
     
  4. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,798

    David Gersic
    Member
    from DeKalb, IL

    A degree wheel?

    The balancer is ok, within about a degree of probable measurement error on my part.

    I have a dial indicator and base, but I’m not understanding what you want me to measure with it.

    Stock ratio rockers, yes. Springs are unknown, I didn’t put them in, so assume stock.



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  5. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,798

    David Gersic
    Member
    from DeKalb, IL

    I didn’t. That’s just what I started with.



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  6. Obviously a degree wheel bolts to the crank, and will not fit on an assembled engine.
    Use the balancer, a timing tape.

     
  7. pprather
    Joined: Jan 10, 2007
    Posts: 1,139

    pprather
    Member

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  8. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,205

    2OLD2FAST
    Member
    from illinois

    Trouble with those∆∆∆∆ is they're just painted on , doesn't take long for chipping and rust to mess up the marks .....
     
  9. sdluck
    Joined: Sep 19, 2006
    Posts: 2,069

    sdluck
    Member

    As some one already stated change the rocker arm ratio
     
  10. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,798

    David Gersic
    Member
    from DeKalb, IL

    1.5 is standard. 1.4, as far as I can tell, does not exist for SBC. 1.3 exists, as a “cam break in” arm. Would that even work?

    It would reduce lift and duration. I guess it’d reduce overlap a bit too.

    That’d be a lot easier than swapping the cam.



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  11. sdluck
    Joined: Sep 19, 2006
    Posts: 2,069

    sdluck
    Member

    Make sure the slots in your cylinder heads have enough room for the pushrods to move some with a different ratio

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  12. jaw22w
    Joined: Mar 2, 2013
    Posts: 658

    jaw22w
    Member
    from Indiana

    NO! for more reasons than I want to type. Just get your valves set correctly. Get your timing sorted out. Your carb set right and live with the cam you have for the summer cruising season. It will be soft on the bottom end until you get some rpm's in it, but it will get you through the summer. Change the cam out next winter.
     
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  13. sdluck
    Joined: Sep 19, 2006
    Posts: 2,069

    sdluck
    Member

    The camshaft does not fit the rest of the engine,there are no tuneup spec for this.You have to just adjust everything until it works best for your engine.Spec are just a base line.If it runs good set it there and it will be happy.
     
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  14. Why ?
    What causes a valve train failure/ “messed up”?
    What exactly was wrong with those parts?

    There’s been other threads on here where guys have indeed verified timing marks and the engines just won’t run without the timing advanced quite a bit beyond what’s considered reasonable. I’m not sure what the causes or reasons are.
     
  15. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,798

    David Gersic
    Member
    from DeKalb, IL

    As bought, the engine ran fine, started ok, idled well, accelerated good, but had lots of valvetrain noise. Either the lifters weren’t pumping up, or the rockers were loose, beyond what the lifter could compensate for, so the lash was wrong.

    There was enough lash clearance that a rocker came off its pushrod. The studs didn’t pull out, they’re all at approximately the same level.

    I attempted and failed to get a good zero lash / lifter preload. So I pulled the rockers off, found some off the pivots were galled. Pulled the pushrods out, found a few were not strait. Not badly bent, but roll them on glass and the ends waggle up and down a bit. Pulled the lifters, found some were pumped all the way up, solid with oil, others were just springy.

    Also found that the valve seals had deteriorated, and bits and pieces were here and there in the heads. Possibly bits of that got in the lifters, or maybe not.

    In looking at the pushrods, all 17 of them, there are at least two different sets. One set features ends that are almost ball shaped. The other set are just rounded at the ends. Yes, 17. Eight in each head, and one bouncing around in the gallery under the intake manifold. Why? I don’t know.

    Short version: the valvetrain was messed up.

    I examined the cam lobes as best I could from top and bottom, didn’t see any damage. Looking at the lifters, which should be softer than the cam lobes, the surfaces aren’t damaged, and there is no vertical wear marking on the sides, so they have been rotating in their bores. Cleaned and placed on glass, they still have a slight crown to them.

    I gambled on the idea that the cam wasn’t damaged.

    Purchased and installed new valve seals, lifters, pushrods, and rockers. Set lash / preload, successfully this time.

    So, now that the rockers are actually opening the valves all the way, I’m experiencing the full effect of the cam, where I was not before.

    Now the trick is going to be finding a tune to tame it enough to live with for the next few months. Then it’s seeming likely that it’ll have to come out.




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  16. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 398

    427 sleeper
    ALLIANCE MEMBER

    David, if it were me, I'd adjust the valve's to zero +1/4 turn preload, set the timing with a vacuum gauge to get the highest reading, make sure the vacuum advance is hooked to a manifold source, adjust the carb if needed and drive it for the season. Then this winter I would yank the engine out and start at square one. Build a 9.5-10:1 short block, then add a top end kit for the desired level of performance that you are looking for. Aftermarket companies like Edelbrock spend a lot of time on r&d on these system's and they work great! A solid foundation and a matching top end will make a happy engine and a happier driver. Make sure to go through and optimize your ignition system too. You should be happy with the results. JMHO tho.

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  17. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,205

    2OLD2FAST
    Member
    from illinois

    Did this ever get sorted out/ improved ?? Update ???
     
  18. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,918

    porknbeaner
    Member

    Or a bad worn timing gear. A worn timing gear likes lots of lead.
     
  19. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,798

    David Gersic
    Member
    from DeKalb, IL

    It’s at the point of running, doesn’t stall in gear, and is good enough for now. Fall/winter/spring, I’ll pull it apart and swap in a more appropriate cam.



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  20. sdluck
    Joined: Sep 19, 2006
    Posts: 2,069

    sdluck
    Member

  21. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,798

    David Gersic
    Member
    from DeKalb, IL

    Yeah, that’s kinda the effect of what I had with the loose valvetrain. They’re not a bad solution to the problem of a big cam in a street car, but that’s not a crutch I’m going to use. I’ll just get a cam better matched to the rest of the car.

    The engine was pulled from a 74 Chevelle. By coincidence, a friend has a 74 Chevelle, with a “police package” engine, and an aftermarket cam. His seems to be working well, and I’m going to see him next weekend. Just hoping the cam card is still in the glove compartment and that he didn’t throw it away. As far as I’ve been able to find, the “police” 350 has the same basic specs as the regular 350. Same compression ratio, same heads.



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  22. Your loose valve train isn’t anything like a Rhoads lifter at all. They are a simple set it and forget it mechanical variable valve timing device.
    Even the late model variable valve timing actuators are simple mechanical things. Computer controls the oil pressure it sees and sensors tell the computer the location of the cams.
     
    427 sleeper likes this.

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