Question about engine.....

Discussion in 'Technical' started by Moneymaker 1, Nov 25, 2012.

  1. baddad457

    baddad457 Member

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    It's fairly easy to check for wiped cam lobes. Run the engine, then remove the valve covers and check all the rockers to see if any are unusually loose. What I mean here is those that are on the base circle of the cam can be slightly loose, but if you've got a wiped cam lobe they will be really loose. You can also tell by cranking the starter with the sprak plug wires off and watching the rocker motion. A wiped lobe will give noticeably less lift to the valve end than those that are fine. A pushrod not rotating while the engine is running is also a dead giveaway that the lobe has wiped.
     
  2. groberts101

    groberts101 Member

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    No to disagree that a wiped cam lobe/s could be an issue here.. but it's been my experience so far that if a cam has been wiped enough to go low on it's base.. you'd likely know something was up right away just from the sound of the non-adjustable valvetrain rattling around. And the oil would probably be a dead giveaway even if it wasn't wiped that bad too.
     
  3. Krazy Comet

    Krazy Comet Tom

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    Unless the base circle or bottom of the lifter(likely)wears there won't be any excess clearance in the valve train, just a non or partially operational valve... Base circle wear is unlikely as the valve is closed and there is no(or at least very little) spring pressure exerted on it...

    Last one I worked on that backfired out the intake because of a wiped cam was a Chrysler 340, that engine ran perfectly quiet... Just last week a friend had a 351M that was clattering because of a worn cam, so it can go either way...
     
  4. Crazy Larry

    Crazy Larry Member

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    No, set the timing with a timing light, and the air-fuel (idle mixture) with a vacuum gauge.
     
  5. 71gold

    71gold Frank Cooper Supporting Member

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    most accurate...(y)
     
  6. groberts101

    groberts101 Member

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    using both simultaniously is even better since we should be using the light to establish baselines and know where we're going with the timing. The motor always knows best what it wants and not many will be the same after all is said and done.
     
  7. GrabA72Mav

    GrabA72Mav Living Our 2nd Childhood

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    Wow I feel for you man! There are alot of GOOD mechanics on here busting there butt to try to help. I am not any kind of mechanic but did have the same type of problem when building my Mav (using a pulled engine). Mine would idle & start fantastic and run to 2000 / 2500 RPM then pop & crack like it was going to blow. It ended up being firing order, the engine was a 302 roller with a dif cam. It needed to be timmed like a 351W? All I'm saying is maybe firing order? Good Luck!
     
  8. jayss10

    jayss10 This is Minerva

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    theres so many wiped cams any more because of people not knowing they need zinc in there oil,some think they can run syn.oil and it wont wear but thats all wrong,if you have a flat tappet cam you need zinc,some are running stp ,but im not sure if theres enough zinc in it ,about the cheapest oil for zinc is rotella ,so id bet on cam trouble
     
  9. Crazy Larry

    Crazy Larry Member

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    Very true, except that Shell Rotella no longer has the high zinc content either, as new Diesels are now equipped with catalytic converters, and the zinc is not good for them. The only way now is to buy a zinc additive, or use off road oil such as what Summit and other mail-order companies sell.
     
  10. Crazy Larry

    Crazy Larry Member

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    There's a reason the timing light was invented, and it's not because a 10-dollar vacuum gauge is more "accurate" for setting timing.

    Running more than 38 degrees total advance on a small block Ford is dangerous and foolish.

    The engine "knows what it wants" for air & fuel, but when it comes to timing, you need to give it what it needs, short of the point of causing damage. If you set the initial timing to 6-12 degrees BTDC and it still doesn't run right, you've got another problem that has nothing to do with ignition timing.
     
  11. groberts101

    groberts101 Member

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    Not that the damage may already be done here and you guys are on to something(though I still think it's not something mechanical and has to do with ignition or fueling)..most all racing oils have decent enough amounts of protective additives to reduce these issues on motors with more conservitive spring pressures.

    I know TONS of guys that still use the old VR1 race oils on MUCH more aggressive builds than the OP's and I also use it myself without issue since most local parts stores stock it.

    Also consider that there are more additive package solutions than just ZDPE alone to help combat these potential issues.

    and FYI.. every motor will have an OPTIMUM setting for lead at various rpm's and throttle angles/parts combo's and even vehicle weight/gear ratio has MAJOR impact for what the combo will allow. I've run more than 50 degrees of idle/off-idle/cruising speed advance(low throttle angle/high manifold vacuum) when you add the vacuum pot into the equation. Generally, but not always, lower compression motors can take much more lead than high compression motors of course.. but even my 11.5 compression 383 currently runs 48 degrees up to about 1,700 rpm(it actually idles better at 52 but will only help up to about 1,400 rpm anyways) under light throttle and then I set the box to pull more lead out depending on vacuum and load and as rpm increases(I use a MAP sensor and laptop to set up the curve on my MSD 7 series programmable box). Which of course makes this apples to oranges for what hardware the OP is using here.. but it does certainly teach you rather quickly what's possible if you have more adjustability to tailer things more accurately and to the specific combo. Even my last stout little 302 ran 44'ish degrees under light throttle(low throttle angle/high manifold vacuum) and it was making 205 lbs of static compression with it's total seal gapless rings and short'ish 224 degree cam. If you already thought you had it dialed in pretty good?.. then the added throttle response and off-idle torque increase will amaze you when you get it right. I will say that the carb will likely go into lean miss condition if you don't screw with air bleeds and jetting when using major low/mid-range advance curves though.

    Ever want to try and discredit this approach?.. simply lock out the ignition advance to about 28-38 degrees with no vaccum pot(again.. every motor is different and some will ping even at low 20's of locked advance) and watch that motor come alive off idle. If doen correctly.. even bigger cams will make more power off-idle than they are supposed to and it makes them much more tractable and fun to drive.

    I have been setting ignitions up this way for years now and all my friends love these types of curves.

    1. Add upwards of 20+ degrees of initial lead(some bigger cams even like more than that since compression bleed makes them more forgiving).
    2. Use a stiffer spring/light weight setup and get the total advance setting to what the motor like for top rpm power.
    3. Add an adjustable vacuum pot which only adds another 5-12 degrees at idle/off-idle.

    Throttle response will go up.. off-idle torque will be higher than it's ever been.. and mileage will increase IF and when you can keep your foot out of it after it becomes so much funner to drive as it chirps the tires even at lower rpm shifts. Those who use lower rpm/near stock stall converters will also sometimes see the extra torque gains on the tach as the motor pushes it to higher rpm and the brake. And when the stall speed rises by about 50-100 rpm over "conventional iginition curve setups"?.. you know your doing something right. :Handshake
     
    Last edited: Feb 24, 2013
  12. junrai

    junrai Member

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    everyone is going with timing and vacuum but what about spark? hows your coil? on an old ford truck I had (one of everything was wrong with it) the coil would give me trouble similar to what youre describing. and have you checked your fuel filter? clean gas and good spark are important. my old truck would idle great and rev right up but you start to put a load on it and hold it you could hear it pop every second or two. I replaced my coil and that stopped it for a while then I found my voltage regulator was letting too much juice go through and it was burning my coil out. another similar problem I had was a wire in the back of the ignition plug was barely hanging in there and was losing connection making it run great one second then lousy the next.

    good luck
     
  13. baddad457

    baddad457 Member

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    You know, now that I think about his problem again, it could be the vacuum advance isn't working too. That's an easy to check thing, remove the distributor cap, unplug the vacuum hose from the carb and while sucking on the hose, watch to see if there's movement in the breaker plate inside the distributor.
     
  14. groberts101

    groberts101 Member

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    but why would that cause popping and backfiring since it's only purpose is to help drivability and mileage since it goes away under full throttle anyways, right?

    In other words.. it's only "supplemental advance under light throttle angles".. and not required to figure out the curve.

    Unless of course he's so far initially/mechanically advanced that the additional advance offered by it is pushing him into the high 40's/50's.. or more... which could certainly cause a lean condition. Lean's will usually just cause misses though.. not out of time backfires/intake pops.

    But you're right.. he needs to troubleshoot in every way possible to make sure everything is working as specified before he moves to harder issues.
     
    Last edited: Feb 24, 2013
  15. baddad457

    baddad457 Member

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    It'll do it because of not enough advance being added. I've had this happen before, I don't recall if it was backfiring, but it sure ran like crap without the vacuum advance working. Just something that's easy to check and eliminate as a cause.
     

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