For those of you that don't know from my other threads...I've got some motor vibrations between idle up to 2500 RPM, with the worst of it being around 2000 RPM. I was curious if the distributor weights/springs/plate are possibly sticking causing my timing to be incorrect until there's enough RPMs to make them open up/work properly. I noticed some intermitten changes in the harmonic balancer position when strobing it at the troublesome RPMs. I've read that a bad distributor can cause vibrations and timing irregularities, which sounds very similar to what I've got going on. Could this be my culprit? I have also noticed recently that some oil gets into the distributor cap and likes to settle on the contact tab of the rotor. Worn shaft maybe? The springs do look kind of nasty. Is there an easy way to troubleshoot this?
i really doubt that would cause a physical vibration. it does sound like you need a new distributor so its not wasted money to replace yours. im still pretty convinced your flywheel is not properly balanced to your motor and heres why. when a motor is being rebuilt some times it gets balanced and some times not. i suspect yours was not. so considering that a different crank was used, i dont know if it was new or a good used one, and new pistons, some thing changed from what the factory balance should be. im also under the impression that the flexplate was changed out after the second rebuild which was questionable because of only some of the lifters being changed out. the fact that the flex plate was changed after the motor was build means that if the motor was balanced during the rebuild the flex plate didnt get match balanced to the motor. i know all this is your worse scenario but its the most likely cause for the events that lead up to the vibration occurring.
I went out today to check my total timing (initial is set at 12° w/ no vacuum advance) and where the timing marks were at different RPMs. At 3000 RPM it was at a steady 34°. At 1500 RPM it was only at about 14° and is fairly rough. I let off the throttle and disconnected the vacuum advance line to VA and put my finger over it. I got it back to around 1500 RPM and then reconnected the vacuum line to the VA, but the speed and timing didn't change any. Sounds like a bad VA to me. What do you think?
that would be for ported vacuum. the motor will run better with manifold vacuum since it will allow more advance under light loads(when the vac pull is higher) and improve part throttle torque/mileage. Then when you open it up to go fast(vacuum drops).. that VA goes away completely(or almost completely depending on how far the throttle plates are opened) and keeps the engine from pinging under heavier loads.
Port vacuum and manifold vacuum is the same once the throttle blade is cracked open. The reason they said Port Vacuum back in the day was to get the exhaust hotter by retarding the ignition timing for better emission reading at idle.
Look at your harmonic balancer. They sometimes let the ring slip on the hub with age. If the rubber is badly cracked, oil soaked or missing chunks, that is my culprit. SPark
LOL if I could figure out how to run a engine on manifold vacuum, I'd be a multi-trillionaire... That said, whether manifold or ported vac is used isn't going to make .0001% difference in the smoothness of the engine, especially running unloaded... To prove this, disconnect vac totally and try different amounts of initial timing from 0 to 25*... I guarantee your vibration will be same... If it isn't there is likely a issue in the distributor... It's not uncommon for these old dist to over advance mechanically, but with that issue in play the shuttering(it not really a vibration) is generally continual from the point it begins onward...
If the timing isn't running past 38*, there isn't a over advance condition... I've seen dist that had over 50* of total timing at 2000-3000 RPMs that caused a shake/shutter but again it isn't like a vibration...
I also spoke with Jeff at AdvancedDistributors.Com and he said: "Ford distributors wear out shafts. Excessive play will be shown in timing variations, and retarded timing above 3000 rpms, growing more retarded as you accelerate. The timing will not be consistent, and you'll have timing variations from cylinder to cylinder. The rotor will touch the cap terminals and misfire. Electronic ignition is a waste of money at this point. Apply it toward a decent distributor."
while that's true at some points in rpm/load range.. to boil it right down.. vacuum advance is load based and mechanical is RPM based. And just because the factory tuned an advance curve to be run with ported vacuum sources?(based on venturi airflow speeds).. certainly doesn't mean that it's best. Emmision regulations and dummy proofing was big part of why they did many things the way they did. ALL of the best tuners in the world due away with ported vacuum sources because they are bandaid solutions which make it necessary to remove a portion of mechanical for the introduction of vacuum used in its place. Robbing peter to pay paul. Of course both can be made to give similar curves if tailered properly.. but you'll never get a boost from ported vacuum under light loads as you would with manifold vaccum. Which makes it FAR superior from an efficiency standpoint. Recurving a disty to an optimum initial and mechanical advance will produce the best power. Period. Then adding an adjustable pot on top of that will allow greater economy/light throttle torque simply because an engine under lighter loads will tolerate more advance during light throttle/lean cruise. Ported vacuum can never do that.
lol.. that's why I ALWAYS shim them. Even the new/reman units ofetn start off with excessive gear to housing clearance. Shims are cheap.. and it's very easy to drive the roll pin out of the gear to tighten things up.
