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Discussion Starter #1
Hopefully someone can help...


  • Complete rebuild on the motor about 3 years ago but not run until now.
  • 289 HP (Shelby version) pretty much stock everything except a mild roller cam and hydraulic lifters.
  • Verified TDC = 0* on the balancer.
  • Dwell is 33*.
  • RPM measured with a DMM though there's about a 200 rpm difference between the DMM and the tach (lower on the DMM) - the tach was just rebuilt and calibrated so not exactly sure which to trust but trusting the DMM for now.
  • Using the vacuum method to set initial and the initial setting on a timing light to measure, the motor seems to like 35* initial at idle (750 rpm) - wow, and 60* all in a little over 2500 rpm. I get just under 15psi of somewhat steady vacuum then backing off the timing just a scosh. Really doesn't want to idle anywhere near smooth with anything less.
  • Have not actually driven the car to check for detonation at the current setting - want to make sure it's safe to do so first.
  • Tuned idle mixture using the vacuum method - seems to like 3/4 turn in from initial 1-1/2 turns out.
  • Had a bad coil but that's been replaced.
  • Valves were set by someone else earlier this year so I can't personally verify.
  • The distributor was not rebuilt, just freshened up, but don't remember having this timing issue before restoration started.
Have I missed anything?

I've run out of ideas, all help welcome.

Thanks!
 

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Needs to be checked with vacuum disconnected. Dwell should be around 29-30. Max timing should be less than 40. 36 would be ideal. I’d bet when you drive it under load you will get significant pinging.
 

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Discussion Starter #6
Needs to be checked with vacuum disconnected. Dwell should be around 29-30. Max timing should be less than 40. 36 would be ideal. I’d bet when you drive it under load you will get significant pinging.
Mechanical advance. Dwell spec. is 30-33, it's right at 33.
 

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As nears as I can tell it is. It's the original balancer and marks are stamped in. I manually set rotating assembly to TDC on #1 and verified 0deg. mark at cast-in pointer.
the balancer has a rubber lining that dampens it a little. The rubber gets old and can allow the balancer marking to rotate and be off, so when it is pointed at 0 degrees, it it not actually 0 degrees.

It sounds like you did actually bring the #1 piston up to TDC and checked the balancer markings.

Does your distributor have a vacuum advance canister on it? If so, it needs to be disconnected when checking initial timing.
 

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Discussion Starter #9
the balancer has a rubber lining that dampens it a little. The rubber gets old and can allow the balancer marking to rotate and be off, so when it is pointed at 0 degrees, it it not actually 0 degrees.

It sounds like you did actually bring the #1 piston up to TDC and checked the balancer markings.

Does your distributor have a vacuum advance canister on it? If so, it needs to be disconnected when checking initial timing.
No canister, mechanical advance.
 

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Cam intalled out of proper alignment with the crank shaft? Would that cause this or if it is retarded, would advancing the timing more sort of compensate for it?
 

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First step is to verify true TDC is where you think it is. Use a piston stop in the #1 spark plug hole and find true TDC. Only then can you verify the 0° timing mark on your damper actually lines up with the pointer. Make sure you don't crank the engine using the starter with the piston stop in place or you could put a hole in your piston.

https://www.amazon.com/gp/product/B000A8FNLI
 

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Discussion Starter #14
Still have this issue...

Any thoughts on what the symptoms would be if the distributor were stabbed a tooth or 2 one way or the other?

Checked the dwell today and it was running at 34deg, adjusted points (dual point dist.) so that it's back to 33deg (gapped from 0.020 to 0.022 but the spec. is 0.020). Readjusted timing with a vacuum gauge and it wanted another 2deg of timing so initial is set at 32deg, yikes! It scares the crap out of me that all in timing is, well, outside the limits of my current toolset.

When out for a run and to be honest it felt like it was running better than it did the last time with no discernible ping, etc.

So, would really like some feedback from those who would know (in been-there-done-that) as to what symptoms I might see if the distributor was actually off a tooth or 2.

Thanks!
 

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NMB, the timing light flashes based on when the distributor sends a spark. When that flashes, you 'see' the pointer and damper. The spark plug wires, distributor position, and even the direction of the bug inside can all be changed around to get the same result. For example, if you pulled out the dizzy and advanced it a few teeth, but then moved all the spark plug wires one over in the same direction, you could get exactly the same timing.

I think what you're having problems with is the fact that you're running no vacuum advance. On pure mechanical, your engine *won't* be perfectly smooth at 8-12 degrees BTDC (Probably 12 or so, given that you're running a Hi-Po). This is because at high-vacuum conditions (idle, with throttle closed) you have very little fuel or air going in the cylinders, and it lights very slowly. It needs the spark sooner, so you reach peak pressure at the right time, just as the piston starts back down. Vacuum advance takes care of all this: more timing when vacuum is high, and less when there's plenty of air and fuel in the manifold. If it's adding in around 24 degrees, since you set your initial to 11, you'd be exactly where you know your engine idles happily: 35 degrees total timing.

If you have no vacuum advance mechanism on the distributor, disconnecting other vacuum hoses certainly won't help anything, so plug your brake booster back in.

Mechanical advance is only 'correct' for your engine at wide-open-throttle. Your engine might like 35 degrees at idle with the plates closed, but when you step on the gas, you have WAY too much timing, and that'll give you detonation. As RPMs and power increase, the problem will get worse, because your peak timing at WOT should probably be more like 40 or so with your Hi-Po.

So - just to break this down - without vac advance, you have a serious compromise. You can time your engine so it runs perfectly with the throttle plates closed, or perfectly with them wide-open. It will never be dead on for any other condition. Generally speaking, with mechanical advance, you wind up focused on the top end timing, because running that over-advanced will blow your engine apart. By adjusting how many degrees the mechanical advance moves, you can get your initial set up so it's a little bit too retarded for closed-throttle (idle) but not horrible for acceleration. Since you should be all-in by 2800 RPMs anyway, it won't be down around idle RPMs for long when you mash the throttle. You set your top end so it's not pinging, and delivering best performance, and then you live with the rest. Cruise and idle will be a bit rough, and you will always use more fuel, but your wide-open throttle performance will be fine, with mechanical only.

If you really want to drive your car around and go cruising, you should strongly consider a vac advance dizzy - even if it wasn't original to the car.
 

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OP, even though you might not hear pinging, etc, there still might be engine damage taking place if your examination of #1 TDC is correct and you are using 50+ degrees of total timing under a heavy load. Now just tooling around town with high vacuum, then you can have 50+ degrees of timing, no problem. But under a heavy load, like WOT, or rapid acceleration in a higher gear, then engine damage is going to occur and you DON'T always hear the warning signs.

FOR HiPo ONLY:

you can run 20 degrees initial timing and still not be over the stock HiPo specification of 40 degrees simply by removing the distributor cam snap C ring, raising the cam up slightly, then rotating the point cam 180 degrees, and lowering it back into position. This will let you use the narrow slot for the mechanical advance pin vs. the wide slot. Most HiPo distributors are marked 14L / 10L on the advance unit. 14L means the wide slot will give you crankshaft 28 degrees of advance. Conversely, the 10L slot will yield 20 degrees of advance. The stock (factory) position is the wide slot, usually marked 14L : = 28 degrees mechanical advance + 12 degrees initial advance = 40 degrees total advance, which is the stock HiPo spec.

By using the 10L slot: 20 degrees mechanical advance + 20 degrees initial timing = 40 degrees total timing.

Regardless of which induction system I was using, Paxton , Weber , HiPo Autolite, or Holley 715. this solution is where ALL of my HiPo's and HiPo based Shelby's ran the best.

Todays gasoline burns somewhat slower than the 1960's formulation, and todays cars normally run lean and use a lot timing.

Furthermore, Your classic car has a cylinder head and cam (usually) that is not as efficient as todays cars which also hinders a rapid fuel / air mixture burn. This is why your engine's rpm will increase when the timing is advanced. You are simply giving the engine more time to burn ALL the gas in the combustion chamber instead of some it going out the exhaust valve unused. If you have a wide-band air / fuel gauge, this becomes readily apparent.

Z

PS:

I think what you're having problems with is the fact that you're running no vacuum advance. On pure mechanical, your engine *won't* be perfectly smooth at 8-12 degrees BTDC (Probably 12 or so, given that you're running a Hi-Po).
with all respect, I think this line of thinking is a red herring. There are thousands of HiPo 289 engines running smoothly and powerfully without a vacuum advance. Do street cars benefit from a vacuum advance ? Yes they do. But not having one will not hinder performace in the ways you suggest. Vacuum advances will help an engine under low load circumstances get better gas mileage, but under heavy acceleration, they might as well not be there.
 

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Zray, you're 'the man' when it comes to SBF's, and I'm not going to disagree with you. But just to add some clarification, growing up with my 302-powered Cougar, and being poor, I worked on my engine every day for many many years, tuning it to the Nth degree.

I ran a 289 dual-point dizzy in my engine for most of that. It always ran great! Or at least it was quick. But if he's tuning for a glass-smooth idle, and has his final set around 60, it's probably not going to end well.

For performance, there's really no difference between mechanical or vac advance at all. But I had better idle, crisper throttle response, and picked up something like 4-5 mpg when I finally added vac advance, so if it's something you drive all the time and care about that sort of thing, you've got my two cents' worth.
 

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PPS:

I may have missed it, but I don't see mentioned what carburetor is being used. If it's a Holley 715, or even a 650, lowering the float levels from the stock Holley recommendation will often cure a mysterious issue. The stock setting is way to high unless you are running full throttle for 20 + seconds at a time. A rich condition, like high levels produce, will cause the engine to run "better" with excessive timing.

NOTE: with a stock Autolite HiPo distributor, the maximum mechanical timing is not even "all in" by 4,000 rpm. Before you go any further, I'd check the distributor timing at every 1000 rpm against the Ford shop manual specification. By the way, the shop manual lists the specs in "distributor" degrees. You have to double those numbers to get crankshaft degrees.

good luck.

Z
 

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Zray, you're 'the man' when it comes to SBF's, and I'm not going to disagree with you. ...."
Pleeease ! I'm not any kind of last word, or authority. I just have a little anecdotal experience, and that, when mixed with equal amount of crystal ball gazing = 99% of my VFM postings.

".....But if he's tuning for a glass-smooth idle, and has his final set around 60, it's probably not going to end well.
we are in complete agreement.


Z
 
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