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Thread: Ignition Timing

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    Default Ignition Timing

    I noticed when I adjust the distributor to get the Ignition Timing to line up the notch on the Pulley using a timing light, that the fastest revs don't seem to occur at the specified place.

    The motor is 20 years old.
    As a motor wears, does the Ignition Timing still need to be in the same place as a new motor?



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  • #2
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    Yes the standard timming settings should be followed if the engine is stock.

    You may need to retard the timming if you have carbon build-up in the heads or poor quality fuel causing pinging (preignition).

    You may need to advance the timming if your running LPG or a higher octane fuel and want to take advantage of the extra power at hand.

    Genrally it stays in the stock position.

    Being a points distribtor your always resetting the timming due to stretch in the timming chain and wear on the points contacts and rubbing block which alters your dwell angle.

    Testing your distibutor advance mechanism;

    There are 2 advance systems, vacuum and mechanical. If one is rooted you wont reach your desired total advance.

    First the vacuum one.

    On the side of the distributor is a round unit with a diaphram inside and a vacuum hose connected to it.
    As a vacuum occurs inside your intake manifold the vacuum travels down the hose to the diaphram inside the unit on your distributor.
    When the diaphram moves, it has a shaft connected to it which goes into your distributor and turns the contact plate to advance the timming.

    To test the vacuum advance.
    Remove your distributor cap and check that the shaft from the vacuum advance is connected to the plate the points sit on.(i have found them unhooked afew times).
    Take a hose running from the distrubutors advance unit, put it in your mouth and suck on it.
    You should see the plate with the points rotate.
    Releasing the vacuum (stop sucking on the hose) should let the plate spring back to its start position.
    This proves the mechanism works.

    Now suck on the hose and while sucking it put your tounge over the hose to hold the vacuum.
    The plate should move as usual and stay in its moved position without going back to its no vacuum position.
    This proves there are no pin holes or slow leaks in the diaphram.

    Another quick shortcut to testing the vacuum advance is to run the engine with a timming light at idle and suck on the hose while observing the timming mark advance while sucking and return to base when not.

    Mechanical advance;
    Under the points plate are 2 weights held with springs, as the assembly spins faster, as engine revs are increased, the weights move because of centrifugal forces and drive a cam that turns your rotor button forward to advance the timming.

    To test the mechanical advance.
    Remove the distributor cap.
    With the rotor button still fitted you should be able to turn it (the rotor button)5 to 10 degrees in only one direction and it should spring back.
    They are known to seize up in older cars and may need to be dissassembled and lubricated.
    I have seen them bind up many times, just disassemble, clean and lubricate it so its free again.

    Another quick way to check your mechanical advance is to disconnect your vacuum advance hose and start the engine with a timming light connected.
    When you rev it hard (higher rpm) the timming should advance.

    So either vacuum or mechanical advance, advances your timming, each a little but it takes both to reach total maximum advance.

    Hope this helps you a little.
    Last edited by Godzilla; 12-09-08 at 09:26 PM.

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    Gee thats a fair response Godzilla.
    Ain't got time at the minute to go through all that, but appreciate it.
    Will respond later but thanks for the actual answer of leave as original.
    The engine is dual fuel so should I advance just a touch if I mainly use gas?
    It runs at 5 degrees before tdc at the minute.

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    what type of car/engine is it?



    Dash.

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    What i do to find the best Lpg settings.

    I advance the timming untill it pings on petrol underload.

    Then i retard it a little.

    My Ford runs with around 10 extra degrees of advance than factory.

    I think i went over it here.

    Post 71

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    The motor is an old Mitsubishi motor 1.6 litre.

    Is advance 10 degress mean advance it even earlier than stock or later than stock?

    I can't do any work with the motor under load.
    How do you load your engine Godzilla?
    Or do you have some sort of electronic control for your timing?

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    BTDC=Before top dead center.

    TDC=Top dead center.

    ATDC=After top dead center.

    The timing marks (scale) is either on your harmonic balance (the wheel sticking out of your crank shaft with the fan belts) or on a cover next to it.

    The scale should have a 0 (zero) in it. When the mark lines up with the zero, thats TDC.

    You want BTDC. When advancing the timing you want more BTDC. IE; The spark to happen earlier.
    So if your engine runs 6degrees BTDC, and you turn the distributor more to 10 degrees BTDC you have advanced the timming....its sparking earlier.

    If you have 6 degrees advanced timing (BTDC) and you turn it to 2 degrees BTDC, you have retarded the timing, the engine is sparking later.

    A good tip.
    When the engine is running at idle speed and you turn the distributor a little, listen to the engine speed.
    If it runs a little slower you have retarded the timing.
    If it runs a little faster you have advanced the timing.

    What do i use to set the timing?
    A timing gun.

    Setting the engine under load?
    Drive and accelerate hard (put the engine under load) from a standing start. You dont need high revs, just load.
    If you have too much advance you will hear a raspy, rattly type pinging.
    If you have too little advance you will lose power.

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    I see.
    And I'm worried I will damage the engine from the pinging.
    Or is that detonating what I'm thinking of?
    I will do a search tomorrow on what pinging is.
    This is quite interesting stuff.

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    Moeee. if you crank up a huge amount of advance and keep flooring it, yes id be worried.
    We are talking flooring it, hearing it AND backing off LOL not pedal to the metal again and again....

    You advance 4 degrees and try it.
    Then another 4 and try it and so on.
    A little at a time.

    Find the point that it pings and then back off 4degrees to where it wont ping.
    Very simple.

    If your seriously worried the stock setting is pretty safe, we are talking about maxamising the lpg setting.

    Dyno tunning is the same thing, they keep a eye out for pinging and back off to a safe point.

    Yes pinging is detonation.

    One other thing is that the timing is set on petrol which cannot take as much advance as LPG. Set it for some advance on petrol without pinging and its more than safe on LPG.

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    Have a look here, post 7,8 etc its a pretty standard technique for dual fuel.




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    Thanks for the Long Reply earlier Godzilla because I wouldn't have checked otherwise.
    Didn't get round to checking the vaccuum advance yet, but the mechanical advance sure is stuffed.
    I wriggled the rotor after seeing that the timing mark didn't really move when I revved the engine.
    And the rotor sort of moves when you wriggle it but it stays where you put it and doesn't spring back.
    I guess a bit of wd40 will get it right, but I do have another distributor laying around if I need it.
    I did notice this engine doesn't really respond to the accelerator as good as my stuffed old engine.
    But it sure does smell heaps better out the exhaust.
    Even on petrol

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    Quote Originally Posted by moeee View Post
    I did notice this engine doesn't really respond to the accelerator as good as my stuffed old engine.
    A classic example of no advance.

    Did you give it enough rpm (over 3000) to get it to move?

    You may be able to remove the contact points plate with the distributor still fitted to the car but im unsure how much room you have to work with.

    If theres room you will need to remove your rotor button, contact points, undo the wires, remove the vacuum advance unit, then look which screws are holding the plate that the points sit on and remove the plate.

    Then you will be able to see the mechanical advance.

    To remove it, its usually just a screw in the hole where the rotor button sits.
    Sometimes may have grease inside and difficult to see.

    Then again distributors are not expensive second hand.
    If it was me id get the spare one out, pull it apart and lube and clean it, put some new points and condenser in and instal the whole assembly as a whole.
    Oh and points are far more easyer to set when the distributor is out and on a bench.

    Then id do the same to the old one and keep it as a spare for emergency.
    Points and condensers are only $20-30 max.

    Have you ever removed a distributor?
    If you plan to remove it please post and lets us know as you will lose you timing position and firing order.

    Its simple to do but you must first understand the timing position of the engine in relation to your distributor and mark some items.

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    When I said engine response wasn't as good, I meant the vehicle didn't accelerate well.
    I guess it is like you said, because the spark is going off too late because of the stuck advance.

    I'm pretty good for removing and refitting the distributor, but the screw in the middle of the rotor.Is it normal thread or left hand thread?
    Plenty times on rotating parts they use left hand threads.
    I remember undoing wheel nuts once and they had left hand threads.

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    Should be phillips head, normal thread.

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    Pulled out distributor and the springs what do the advance were broken and floating around with some piece lodge.
    Other pieces were missing, probably dropped out when I lifted the distributor cap.
    The bit that the rotor sits on was very firm and difficult to remove after undoing the screw.
    Some lubrication and cleaning there and replacing the springs from my spare distributor.
    Could have put the spare in, but seeing as I had 2 of 'em both in bits I thought I might make the original one good again.

    Thanks for the long over earlier Godzilla.
    Wouldn't have gone this way if not for your suggestion.
    Apart from the smelly hands, this is great fun.

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    Good to see you sorted out the problem.

    On a side note your a lucky man.

    Most times ive seen the springs break or counter weight come off resulted in the the car breaking down on the side of the road.

    It shears the pin holding the gear drive on the end of the distributor inside the engine if the broken part jambs inside the dizzy casing.

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    Great informative posts there Godzilla

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