HEI distributor tuning problem
 

I switched to a HEI dist. About a month or so ago and I can't seem to tune out the tapping at the 50-55ish speed. I have played with different base timing settings. I have tried a different vacuum advance module? and even went to the heaviest springs in the distributor.
I'm thinking maybe the distributor is just bad?
The motor (350) does have some kind of performance cam in it, maybe that's effecting it? (Vacuum)

Any thoughts?

Thanks!
Joe
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Re: HEI distributor tuning problem
 

Joe, What does tapping mean? Lee

Re: HEI distributor tuning problem
 

what does it do without vacuum advance connected? Still ping?

Also since it has a performance cam, did it get head work too....compression?

Re: HEI distributor tuning problem
 

Valves tapping?
I thought I was having some other noise problem but after reading about another member with same symptoms it dawned on me what it was.
If I disconnect the vacuum advance and cap the port it doesn't make the noise, it just goes to 5 MPG...
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Re: HEI distributor tuning problem
 

Compression is 180, give or take a lb or two at all 8 cylinders.
I haven't tried high octane, but if it needed higher octane it would ping a lot more often... I would think anyways...
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Re: HEI distributor tuning problem
 

I'm taking it that it did not do this with the other distributor? Did you do any maint (assure the shaft and weights were free, etc) to the HEI? Is the gear orientated correctly? Is the advanced stop in tact? Is the shaft end play excessive?

Re: HEI distributor tuning problem
 

I know it may be a redundant question, but before you put the distributor in did you take cylinder one to TDC? It really sounds like you are still out of time a bit something like about 12-16 degrees. I ran into this once.

Re: HEI distributor tuning problem
 

did you verify the initial timing was set properly with the advance disconnected?

Re: HEI distributor tuning problem
 

To be honest I don't know if it did the same thing with the other distributor, because I also changed the exhaust to a quieter one because I couldn't hear crap over the other one. In fact you can barely hear the noise with the quiet exhaust.
The hei is new and seems fine. Shaft fit good, no excessive play.
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Re: HEI distributor tuning problem
 

Yes I did the initial timing with the advance unplugged and I capped the port.

Yes on the tdc question.
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Re: HEI distributor tuning problem
 

As Lee H mentioned if it was a used HEI.

The last used one I got the grease was so dried out it was preventing the mechanical weights from springing back. They would move but sort of stiff.

Check carefully for vacuum leaks and with a "dial back" timing light check regular and total timing. If you don't have one, rent one or borrow one. It's easier to see total timing with one of those.

As far as using higher octane, it's more expensive but one tankful would let you know if that's your problem. .

Re: HEI distributor tuning problem
 

If you have a timing light with dial up advance on it, start the truck with timing light connected and vacuum disconnected and plugged.

Bring the RPM up with the light on the timing mark. You should see it moving advanced. If it doesn't check weights and springs. If it does and still only goes 5 MPH, pull the module.

Re: HEI distributor tuning problem
 

Just a thought but did you mark the Harmonic Balancer when you brought it to TDC?Occassionally the rubber in a HB will allow the outer ring to slip,giving a false reading of timing.

Re: HEI distributor tuning problem
 

Thanks for all the help!

Sounds like I need to get one of these dial up timing lights.
Longhorn70, you misread my post on 5 mpg when vacuum advance is disconnected, gas mileage suffers greatly when the advance isn't connected.

There is a notch/groove in the HB and it matched up during tdc, I have added the timing tape to that.


Since I have the heavy springs, which are supposed to hold the advance from fully advancing until 3,200 rpms, maybe its the weights? Because basically its going into full advance too soon, thus causing the tapping? Am I understanding this correctly?

Thanks!

Re: HEI distributor tuning problem
 

That's the way it should work. A dial back timing light would let you know for sure. Be sure and read the directions on how to use it.

The tapping descripton is still a little confusing to me. When the engine is too advanced the noise I usually hear sounds like a pinging or rattling chains sound. A tapping sound is normally a loose rocker, piston slap or something not tight.

Re: HEI distributor tuning problem
 

If you have a new HEI, chances are you have an adjustable vacuum advance can. To set the vacuum advance you need a 3/32 inch allen wrench. The adjustment screw is located inside the can, down the vacuum line port. You start by setting the vacuum advance to 0 degrees by turning the screw all the way in until it is lightly seated. Then unsrew it to the desired amount of vacuum advance. On my Accel vacuum can, each turn out equates to something like 2 to 3 degrees of vacuum advance. If your HEI did not come with the vacuum advance curve and adjustment directions, you can go online and find these for the Accel units. By adjusting the vacuum advance, you can possibly remove the detonation without messing with your initial timing or mechanical advance.

Re: HEI distributor tuning problem
 

Yep been there done that even tried another vacuum advance just to rule that out.
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Re: HEI distributor tuning problem
 

I gotta quit inhaling gas fumes.........

Another thought, too "hot" a spark plug could do this too. When this happens you will see whitish flakey deposits on the plugs. Or white/grey build up on the center electrode if I remember correctly.

For grins, have you tried octane booster to find out if it is ping or detonation?

Re: HEI distributor tuning problem
 

I just have regular ol spark plugs in it. I didn't go up in heat size or anything.
I'm fairly positive on detonation. It actually makes kind of a tic tic tic sound. Another bit of info, once its good and warmed up, as in after driving 20 miles or so, it doesn't seem to make the noise anymore. I thought maybe its a oil issue, as in oil is thick then thins out once hot. HOWEVER, when its making the noise, all I have to do is pull over, unplug the advance, cap the port and away I go with no noise. So it can't be a oil issue.

Re: HEI distributor tuning problem
 

What brand distributor is this?
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Re: HEI distributor tuning problem
 

I have the same exact problem! That tapping noise happens when you are sort of maintaining that 50-55 mph? If you still have the links to where other people had this problem and feel like PMing them to me it would be appreciated it. I haven't tried to fix it since it only happens at that one speed.

Re: HEI distributor tuning problem
 

The distributor is from Skip White Performance, the last distributor you'll ever buy! I researched it on here before I bought it. I couldn't find anyone with a bad one. Found post bashing them, because they're so cheap (pricewise) but overall quality looks great, billet shaft, decent parts, etc etc and warranty to, they will swap it, I already talked to them. Just worried the result will be the same since I tried a different advance can and springs.

PM sent

Re: HEI distributor tuning problem
 

This is weird....Usually detonation INCREASES with increased engine temp. Yours seems to be going against that.

Most people install colder heat range plugs in mildly built engines is to alleviate detonation caused by increased head temperatures. I have colder plugs in the Olds engine in my truck and that has helped me get rid of ping.

I have a Skip White 6503 on the Olds. I haven't had pinging problems with it either. That distributor has performed well for me.

Could you be running too lean while cold and when it warms up all is good? Like the heat riser isn't there/working or the choke pulls off too soon?

Please post the solution to the issue when you find it.....I gotta know.

Re: HEI distributor tuning problem
 

subscribed!

Re: HEI distributor tuning problem
 

big difference in quality from something like a shippy chinese and a real quality unit like msd pertronix


THE BITTERNESS OF POOR QUALITY REMANINS LONG AFTER THE SWEETNESS OF LOW PRICE IS FERGOTTEN

Re: HEI distributor tuning problem
 

Maybe it is to lean when its cold, but my choke is a manual and I probably tend to leave it on longer than I need to, just to help warm up the motor. In the morning especially, I let it run a few minutes before heading out.



[QUOTE=cdowns;5933044]big difference in quality from something like a shippy chinese and a real quality unit like msd pertronix
I hear ya, I was extremely hesitant about buying it, I asked around on here and no one had a problem with theirs. Maybe, I should swap it out for another just to see if its a bad distributor. I will have to say I was surprised at the actual quality of it. Looking it over carefully, it looks pretty good, metal and plastic parts are all pretty solid, not super thin or cheap feeling.



After bouncing PM's back and forth with CB1987, I'm leaning towards a vacuum issue. I need to research my carb and make sure I'm on the right port or maybe switch to a port on the intake manifold or something.
It's been a busy week and I haven't had time to mess with it unfortunately. I drove it almost everyday for two weeks with it making the noise so I'm scared I might have damaged something or that it is damaging it. So I parked it for a few days until I can mess with it more.

Re: HEI distributor tuning problem
 

Well, I finally had a chance to read up on my carb, the edelbrock 1405, I have 3 ports on the front; a ported vacuum, pcv port and full time vacuum port. Well its plugged into the full time vacuum, that's got to be it. It's supposed to be on the ported vacuum. I should have time to try it out tomorrow, so I will let you all know what happens.

Re: HEI distributor tuning problem
 

Here we go again with carburetor instructions telling us how to time our engines. Holley instructions do this too, or at least used to.
You can only plug it into the place where the distributor is calibrated to work.
While I am firmly against running ported vacuum, if that's the way the distributor is set up, that's the easiest way.
It's not the best way though, it leaves performance and fuel economy on the table. Setting up your distributor to work with full vacuum will gain you the most.

Re: HEI distributor tuning problem
 

The distributor instructions said to use a ported vacuum.
Could you explain why your firmly against using a ported vacuum?
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Re: HEI distributor tuning problem
 

Alright I'm ready to give up.
I put a new GM hei dist in and I still have the problem. So its something I'm doing.
With the advance unplugged and port capped I have that intial timing set at 12 degrees ahead. When I plug in the advance it jumps to 30 ahead. So a 18 degree jump.
I have adjusted the advance can all the way in and I'm still getting the detonation sound at 50-55 MPH.
I switched to a ported vacuum and it pings like heck so its back on full vacuum.
I haven't gotten a dial back timing light yet, frankly I can barely use a regular timing light it seems. I do have a timing tape on the balancer.
What am I doing wrong and/or what do I need to do?
Thanks
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Re: HEI distributor tuning problem
 

ttt
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Re: HEI distributor tuning problem
 

did you use the power wire off the other original coil? you should be running it off the fuse panel if you have not i know i had that issue when i converted mine

Re: HEI distributor tuning problem
 

nope, ran new wire, 12v feed.

Re: HEI distributor tuning problem
 

ttt
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Re: HEI distributor tuning problem
 

Yes, but be forewarned, it's heavy reading.

Here's an interesting article on vacuum advance written by a GM engineer:

As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.

Re: HEI distributor tuning problem
 

Saying "new GM HEI" distributor means nothing. There are many different models, all with different calibrations. The advance comes in at different RPM and at different rates. You really need to know what you have before you can even attempt to modify it.

Re: HEI distributor tuning problem
 

My buddy and I went round and round with this a few weeks back. We then incorporated the help of an elderly gentleman. Words of wisdom....never under-estimate the knowledge in our elders.

You have to look at all three aspects of your timing. (initial, centrifugal and vacuum). You need to know what your total timing is at 3000+ rpm (all in) and with and with out a load on the engine. You may be at 12* inital and have 18* vacuum advance. But how much is your weights advancing? You need to check it with vac advance unplugged and capped. Use your timing light and get the timing at 3000 rpm. Then....hook a vacuum pump to the vacuum advance can and pump it up to see where it puts you timing will all of the advance added in.

Re: HEI distributor tuning problem
 

Thanks Longhair and JoJaboy.
It's taking a minute for all the timing info to get through my thick skull.
I also really need a tach so I can get a better handle on what rpm's I'm at and so forth. It's been on my list since I bought the truck.
I don't have a vacuum pump either. They can't be to much, I will look into getting one, but I think I can get some readings anyway with out it, just by unplugging the advance vs plugged in advance.
Anyway, I will do my best to figure out where its at and when (timing/rpm) and post my findings.

Thanks again!
Joe

Re: HEI distributor tuning problem
 

It's not exactly the same. When you rev your engine in park, the engine isn't under any load. So the vacuum is different. Short of hiding under your hood with a timing light while your wife takes the truck for a drive.....You can get a cheap $5 vacuum pump and pull the vac advance can in. This will simulate the intake creating different vacuum till all in.

Sure beats hanging on to the headers while straddling the fan and wife at the wheel.

Re: HEI distributor tuning problem
 

Bo wha'cha talking about?! its under load, the bed is slap full!!

The vacuum pump; just give it a couple pumps? that small advance can can't require to much vacuum?