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Technical Initial timing degree for small block chev w points

Discussion in 'Traditional Hot Rods' started by Nailhead A-V8, May 26, 2019.

  1. Nailhead A-V8
    Joined: Jun 11, 2012
    Posts: 824

    Nailhead A-V8
    Member

    Sorry for the seemingly ridiculous question but if you want a real exercise in frusteration search the Hamb, then Google this query, then ask it on several other websites....grrr fuck ...the first suggestion seemed a little strange calling for ATDC but forgive me I was a Ford guy for years so I thought ok i'll try it:rolleyes: it fired right away but after smoking all the paint off my headers and probably burning a valve or two I realised this was dead wrong:mad: (thanks interwebs!)...so the search began 4 deg. , 6 deg., 8 deg., 12 deg and everything in between! ...specs are '80 350 LS9 pass. dipstick, 165 hp all stock 8.2:1, Qjet, headers, A/T the only difference from stock being headers, points ign. and MSD coil even if I could find the stock specs I don't know which to use because the '80 cam is so different from a '73 and earlier points eng. (almost 100 hp) and the '80 specs would be for HEI...any clear and concise suggestions would be appreciated! ...oh points and plug specs would help too...right now its at 0.17 points, stock hei plug gap and 12 deg. btdc starts ok and idles high but seems shaky and rough -Thanks and yes it's in a hot rod:)
     
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  2. Well, if I'm reading you right you're running points ignition, but the plug gap is set for HEI? There is a difference in plug gaps between conventional (traditional) points ignition and HEI. Points-driven plug gap is around .035, HEI is like .06o. There may be other things too, but if it was me I'd start with that. As far as timing, I've always done it by ear. Or using a vacuum gauge. But then, I may have been wrong all these years too. :rolleyes:
    Best of luck, and keep us posted.
     
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  3. olscrounger
    Joined: Feb 23, 2008
    Posts: 3,495

    olscrounger
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    ^^^^ start here--good advice
     
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  4. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,462

    V8 Bob
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    First thing is to set the points by dwell, which is 30 degrees if a stock Chevy distributor. Now you know the point gap is correct.
     
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  5. F-ONE
    Joined: Mar 27, 2008
    Posts: 1,871

    F-ONE
    Member
    from Alabama

    Are you running through a ballast or resistor wire?
    Points need them or they will not live long...not sure about the 80 stuff.
     
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  6. Truck64
    Joined: Oct 18, 2015
    Posts: 3,559

    Truck64
    Member
    from Ioway

    The initial timing # is only a small part of the equation, need to find out what it's doing at 1000, 2000, 3000+ RPM, just about anything between 5° and 20° BTDC will work fine, depending on other factors it will be too advanced or retarded. Neither is any good.
     
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  7. deuceman32
    Joined: Oct 23, 2007
    Posts: 279

    deuceman32
    Member

    All good advice so far. Yes, gap plugs at .035 to start. Yes, set points using a dwell meter to 30 degrees. Now, the timing is simpler than you think, but you need either a degreed harmonic balancer or, better yet, a timing light with an advance dial-up feature. Your engine will want around 36 crankshaft degrees (plus or minus 2) of total mechanical advance, all in. To get there, disconnect and plug the vacuum advance hose, dial the timing light up to 36 degrees, increase engine speed while strobing the timing scale on the engine until the mechanical advance is "all in", and while still at that engine speed, turn the distributor to align the engine's marks at zero (TDC). Now, let the engine fall back to idle, turn the timing light back to zero, and read your new advance setting at idle on the engine's timing tab. That setting is what gives you 36 total with your existing distributor. It is the total advance that the engine cares about under full power. Now you have a fresh frame of reference to start from. Reconnect the vac advance, optimize your idle mixtures with a vacuum gauge, and go for a drive. You could then drop back 2 degrees and see if it feels better or worse. If you get no pinging under load, you could go up 2 and see how it feels.
     
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  8. deuceman32
    Joined: Oct 23, 2007
    Posts: 279

    deuceman32
    Member

    I hope that made sense. Once you know how much total advance the engine likes, then you can start tuning on the centrifugal advance "curve", which is the combination of the amount of available centrifugal advance and how quickly that advance occurs with engine speed as determined by weights and springs in the mechanism.
     
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  9. deuceman32
    Joined: Oct 23, 2007
    Posts: 279

    deuceman32
    Member

    By example, the old Mallory double life dizzys that we all love, in SBC applications typically provided around 24 crank degrees of centrifugal advance that started to happen at 1000rpm or so and was all in at around 2400rpm. That was my experience anyway. So if my engine liked 36 total, then my static setting was 12 BTDC, when running that distributor.
     
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  10. Nailhead A-V8
    Joined: Jun 11, 2012
    Posts: 824

    Nailhead A-V8
    Member

    it's hard to do by ear with open headers if anything it might be dieseling a bit, I have a vaccum gauge but was still hoping to find an initial timing baseline mark and go from there later this is just for first start up and warm up purposes

    will do but you need the engine running at some adv/ret setting for that don't you?

    yes I wired a 12v from the starter for start and then a .08 ohm ballast for run

    Thanks that's what the internet said ;-)

    will do and will do but don't have the fancy timing light for the rest

    so .035 plugs, 30 deg dwell which will also determine the points gap in the process... any suggestions on initial timing degree and rpm to run it at while I set the dwell?
     
  11. 1973 truck 350 tune Up specs are a good baseline to start with, engine specs are close enough, then go from there.
     
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  12. Nailhead A-V8
    Joined: Jun 11, 2012
    Posts: 824

    Nailhead A-V8
    Member

    yeah thats what I have it at right now but I think its not happy ...its a stock GM points dist. year and application unknown
     
  13. Truck64
    Joined: Oct 18, 2015
    Posts: 3,559

    Truck64
    Member
    from Ioway

    ...And this is why you should check & verify what the mechanical advance is actually doing through the RPM range. Without knowing this it's just guessing, where the initial timing # ends up is not critical.
     
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  14. Nailhead A-V8
    Joined: Jun 11, 2012
    Posts: 824

    Nailhead A-V8
    Member

    Thanks... that's with the advance disconnected I realize I will have to do all that stuff later with a different timing light or by pulling the springs ...but right now I want to run it to test the rad, trans etc. just looking for a setting that will be a baseline
     
  15. Nailhead A-V8
    Joined: Jun 11, 2012
    Posts: 824

    Nailhead A-V8
    Member

    This all I was able to find :
    8-350 145hp
    R44T -.035
    10
    29-31
    18436572

    -
    600D
    8-350 175hp
    R44T -.035
    10
    29-31
    18436572
    12°
    -
    600D
    my 165 horse is in the middle... so 10 deg. btdc? w advance disconnected?
     
    Last edited: May 26, 2019
  16. jaw22w
    Joined: Mar 2, 2013
    Posts: 833

    jaw22w
    Member
    from Indiana

    Initial advance (what it idles at) + Mechanical advance (what the centrifugal weights put in) = Total advance (34 to 38 for just about every chevy in the world). All in by 2800. Make sure your timing is all in by 2800, (via springs on the weights) then run it up to 3500 and set the timing at the 34-38 at the damper. Let the initial fall where it may. Doesn't matter as long as it doesn't buck the starter. Mine is set at 18 initial+16 mechanical = 34. My mech adv is limited to 16 degrees and my vacuum advance is limited to 14 degrees. It's pretty easy to do. Don't mess with vacuum advance until you have the initial and mechanical all sorted out. Initial + mech = 34 + vacuum advance = 48-52 degrees.
    As being discussed currently on another thread, I would check the accuracy of your top dead center mark and pointer.
    Set the dwell at idle.
     
  17. Jimbo17
    Joined: Aug 19, 2008
    Posts: 3,545

    Jimbo17
    Member

    I like using a vacuum gauge because it takes all the guess work out it.
    Guys say they can hear a 100 or 200 RPM change and my ears are just not that good to do that.

    Jimbo
     
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  18. deuceman32
    Joined: Oct 23, 2007
    Posts: 279

    deuceman32
    Member

    With your stock GM points dist, I would start at around 8 degrees initial while you sort it out. Is this a first fire up of a fresh engine with new rings, etc? New flat tappet cam?
     
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  19. Nailhead A-V8
    Joined: Jun 11, 2012
    Posts: 824

    Nailhead A-V8
    Member

    so using my vacuum gauge the advance pod is hitting the manifold I cant advance it any farther... I took the wires off the cap and moved #1 over 1 post in either direction to no effect in order to get it to run even close to full vacuum I have to have it straight up against the manifold...when I had the dist. sitting with the vacuum pod pointing roughly at #6 where I usually see them it scorched the paint right off the headers and ran like shit
     
    Last edited: May 26, 2019
  20. Forget the vacuum method for now. Too many techniques mentioned here..Ya got the boy confused.
    Put damper timing mark at about 10 * before 0 mark on the timing tab , intake stroke . Pull the cap off . Set the dist. in ,where you have plenty of room to move it either way. Snug it up just a bit. Line your no. 1 plug wire on cap with the rotor blade tip. Wire the rest in sequence.
    Put your tach and dwell and timing light in place. Fire it up . Set idle up just enough to keep it running when warmed up. Set dwell again. Now check timing at idle . Should be about 8-12 . Don't worry about a degree or two. Plug in vacuum advance now. Idle should go up, so re-set it now.
    There are no specs anymore. You have to make them up as you go.
     
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  21. Nailhead A-V8
    Joined: Jun 11, 2012
    Posts: 824

    Nailhead A-V8
    Member

    Thanks @Mark Yac I understood every bit of that and will try it before the next recommendation which is to pull the dist. again and line up some dimple thing with the rotor...
     
  22. Nailhead A-V8
    Joined: Jun 11, 2012
    Posts: 824

    Nailhead A-V8
    Member

    went to the older #1 position but then my coil started leaking:( leading me to believe it's still a tooth two off and is arcing inside the cap and heating up the coil...so I guess it's back to the drawing board pulling dist. and #1 plug - TDC yada yada yada again...
    https://www.jalopyjournal.com/forum/threads/chevy-350-distributor-question.291353/
    #1 @ 7 o'clock position
    plugs - 0.35
    points - 0.17- 0.19
    dwell - 30 deg.
    initial timing 4-10 deg. btdc
    matching balancer and pointer
    dist. stock pulled from runner so not likely rotor/gear is 180 out
    I've got all the parts to the puzzle and done this all the ways previously suggested but still cant get any more advance:confused: ...so after I redo everything where should the vacuum pot sit? half way between the firewall and manifold? pointing straight at the fenderwell? I think that's what I did before and it was so retarded I thought I was going to destroy the engine when it fired up:mad:
     
    Last edited: Jul 8, 2019
  23. Ericnova72
    Joined: May 1, 2007
    Posts: 128

    Ericnova72
    Member

    From where you are right now....remove cap, remove clamp that holds distributor into motor. hold rotor lightly to just stabilize it, then use other hand to slowly lift the whole distributor up about 3/4" to 1". As you do this you will feel the rotor slightly turn as it follows the helix cut of the gear mesh. Using that feel on the rotor as you lift, you'll be able to feel the point the ear is lifted high enough it reaches the end of the gear tooth contact and comes loose. At that point, stop lifting, and you will be able to turn the rotor clockwise slowly and feel it "skip/bump" over to the next tooth in line. Rotor tip moves ahead about 1/8".
    When you feel it skip over to the next tooth, stop right there, put the distributor body back down into the engine. Now, it may or may not not fully seat, due to being out of alignment with the oil pump drive tang, but don't worry, we are going to fix that next. If it does manage to re-align to the oil pump drive, skip this next part.
    Using the starter, bump the engine over enough times to get one full revolution on the rotor and it will find it's own alignment with the oil pump drive and then drop fully back down into place. Put the hold down clamp back on, put the cap and wires back on, and fire it up.
    You'll find that the timing has jumped up 15 or so degrees from where it was set before, which will now allow you to retard the vacuum advance can orientation back toward the firewall in order to get you initial timing back to the usable range of 8 to 14°.
    The fact that removing the distributor many times the oil pump drive will wind backwards just a tiny bit, so then when you re-install the distributor you often inadvedently back the rotor up one tooth in the process of getting it to go all the way down onto the pump drive.....and that is what messes a lot of less experienced guys up. They are worried too much about getting it all the way back down before turning anything, but as long as the gears are back in mesh the oil pump drive doesn't matter for the next 2 minutes.
    If you ignore the pump drive alignment, put the rotor and housing pointed where they need to be, and then bump the engine around with the starter one full revolution on rotor it will find the pump drive and align itself, easy-peasy.

    Same methd works to also back the rotor up one tooth if you've got it over advanced and the housing won't let you rotate it back anyfarther to fix the timing when chacked. This is often even easier to do, as the tendency for the oil pump to turn itself backwards a small amount will often let you drop the distributor right back down fully after skipping the tooth back, and if not it will just take one little starter bump forward and presto, the housing drops into alignment.

    This whole deal takes longer to explain than it does to just physically show someone how easily it is done.

    If that is a stone stock 1980 engine from a light truck or passenger car, the cam is the exact same cam that is in the 1973 engine(the "979" cam). Would have to be an L-82 Corvette in those years to have any bigger a cam. Power differences in those years are due to carb and intake, valve and port sizes in the heads, distributor timing curve and emissions settings/equipment, and what dyno rating factor they used....but the base engines are essentially identical.
     
    Last edited: Jul 8, 2019
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  24. jetnow1
    Joined: Jan 30, 2008
    Posts: 1,315

    jetnow1
    ALLIANCE MEMBER
    from CT
    1. A-D Truckers

    Was this engine rebuilt or is it original? There were several different balancers and timing mark tabs
    used over the years, more than one engine has been assembled with a mismatch. As stated in several
    different posts, the initial setting is not that critical, has long as it is somewhat reasonable.
     
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  25. distributorguy
    Joined: Feb 15, 2013
    Posts: 28

    distributorguy
    Member
    from MN

    This is an all too familiar scenario for me. You likely have a distributor with a horrible advance curve, so there's no throttle response from the advance mechanism doing the entirely wrong thing. Do you have a different distributor you can install? I find most SBCs like 16 timing at idle, 36 total, with small variations for different builds. Your distributor may have as much as 30 degree of mechanical advance, so you might have to set base timing at 6 BTDC for it to run well from 3000 rpm and up? That's why you're finding so many different specs for base timing: the amount of advance in the distributors varied for different applications. You may have a truck or station wagon distributor that's not meant to give good performance - at least not without being recurved.
     
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  26. Did you verify this with a piston stop test?
    IDGAF what a timing light says until that piston stop test is done.

    You’re mixing and matching parts in a custom build so that means you need custom specs and possibly recurve the distributor. How do you know ???? Forget your initial timing for the moment and Set the total timing to 36 all in by 2500 rpm. Now you’re initial timing is what the distributor curve says it is. You’re going to live with that initial timing if you can or recurve the distributor.

    It’s that simple and doesn’t take too long to figure this out. 10-15 mins for stop test,,,, 10-15 mins for total timing and some fiddling then get your initial timing read. 30 mins total and you have solid foundation and solid knowledge to base your next decision on.
     
    Last edited: Jul 8, 2019
  27. Kan Kustom
    Joined: Jul 20, 2009
    Posts: 2,290

    Kan Kustom
    Member

  28. Truck64
    Joined: Oct 18, 2015
    Posts: 3,559

    Truck64
    Member
    from Ioway

    Sir, that's just crazy talk!

    I suggest maybe a "ported or manifold?" Vacuum advance debate is in order, so this thread can go off the rails.
     
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  29. Have at it, I’ve got real problems lol
     
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  30. Deuces
    Joined: Nov 3, 2009
    Posts: 17,692

    Deuces
    Member
    from Michigan

    Hook up the vacuum advance to manifold vacuum... There, I said it!... Never had a problem doing it that way.....
     
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