Strange timing issue

[Troy P.]

For years now I've been befuddled about the ignition timing on my 63 fuelie. To get it to idle and run reasonably it takes way more advance than specified. When I say way more I mean like 30 degrees at idle with the vacuum advance line blocked off! I've just discovered the same issue with the newly rebuilt 265 V8 in my 55. I don't get it. What is going on?

I don't live at altitude, maybe 2500 feet.

Since two cars exhibit the same strange behavior I thought maybe my timing light was screwed up. So I bought another one and got the same results. Double checked to make sure I hooked it to the correct spark plug wire too.

On my 63 I thought maybe the harmonic balancer had slipped. Also thought maybe I have the wrong timing cover and the timing tab is in the wrong place. Doesn't seem like either and very odd that I now have another engine doing the same.


Any ideas?

[Terry D.]

Re: Strange timing issue

Did you check to see if your distributer is off a tooth? That's what it sounds like.

[Mark E.]

Re: Strange timing issue

Did you check to see if your distributer is off a tooth? That's what it sounds like.

The distributor indexed differently with the cam won't cause this. Ignition timing is only affected by the relative position of the rotor and cap.

I'm not sure what's happening. Did you or the same person build both engines? Maybe the timing tab is misaligned? Have you checked the piston for true TDC?

Are you sure you're connecting to plug #1, not #2?

[Duke W.]

Re: Strange timing issue

The OE centrifugal advance is start @ 700, 24 @ 4600. So to set initial timing, you have to get the engine below 700 long enough to measure and adjust, which is very difficult to do because high overlap cams usually won't allow the engine to idle stably below 700 long enough before they stall for you to finish the job.

That's why I recommend setting total WOT advance (with the VAC hose disconnected and plugged with a golf tee) a few hundred revs above the point of max centrifugal. With the OE springs that will be about 5000, but if you install lighter springs, not only will low end torque improve, but you can set total WOT advance at much lower revs.

The ...375 FI unit is set up for ported vacuum advance. I have no idea why, but clearly Chevrolet realized this was a mistake, and the ...380s are set up for full time vacuum advance with a 8" VAC that passes the Two-Inch Rule.

This may be part of your problem, so I recommend you convert to full time vacuum advance, and you will need a 8" B28 VAC (Airtex 4V1053) to pass the Two-Inch Rule because the 15" OE 201 15 VAC does not pass The Rule.

Duke

[Troy P.]

Re: Strange timing issue

Absolutely sure I'm on No.1 plug.

On my 63 I found years ago when I bought it the vacuum advance can had a dent in it and it was right against the air plenum. This was a dead give-away the distributor was not installed correctly. I think I also found that to help correct that Bubba may have moved the ignition wires in the distributor cap one cylinder. I corrected that years ago. Then I think I found the distributor gear was on backwards (180 degrees out), which I seem to recall amounts to being off by about 1/2 a tooth or so. Still after all that the engine, per the timing light, needs way more advance than the 10 degree BTDC spec. So I've "tuned it by ear", so to speak, and have lived with it for a decade or so.

Now I have this newly restored 55 with a similar issue. Specs are 4 degrees BTDC but I've been told it really takes like 10 degrees to get it to idle down around 600-650 rpm. Timing set that low the car won't even start without great effort. Timing "by ear" the distributor likes about 30 degrees and it starts fine (carb choke problems aside).

Perhaps this distributor is not set in correctly or gear is upside down or wires have been moved on the cap.

Moving wires on the cap changes timing 45 degrees. Please remind me how many degrees one tooth on the distributor changes timing and also how much change does a rotated distributor gear produce. With those numbers in mind I'll try to approach this analytically.

[Duke W.]

Re: Strange timing issue

The way to approach this "analytically" is to verify that the wires are indexed IAW the '63 shop manual. Then place the crank at 10-15 degrees BTC on number one. Remove the dist. and verify that the dimple in the gear is pointing the same direction as the rotor tip. Correct if required.

Reinstall dist. and when seated rotate the base until the points just open. This will place the initial timing within the 10-15 deg. range. Snug the clamp enough to still allow rotation by hand and check and adjust timing as necessary.

Duke

[Edward J.]

Re: Strange timing issue

Troy, years ago I rebuilt my 340 shp and used a seal power camshaft and had a problem with not being able to get my timing set to spec. the movement is very limited, on our cars, I had a the vacuum can against the intake, all the wires were in the correct position on the cap. the end result was to rotated the dist. gear 180 from the dimple. The index of the after market cam was not as the factory, I believe that Duke was the one that told me this.

[Terry D.]

Re: Strange timing issue

Troy
I would start with the basics, Make sure number one piston is at top dead center. See where your rotor points to. Make that your number one plug wire. Wire the cap according to firing order. Then check your timing and let us know the results. If this does not let the vacuum can be in the right place they your distributor is off a tooth or two, and it does make a difference. There are some very good articles by Lars Grimsrud and John Hickley at Corvette Restoration.com or just google Lars Grimsrud

[Timothy B.]

Re: Strange timing issue

Troy,

My thoughts are rotor phasing and camshaft valve timing. Are you using points vs an electronic trigger because that could fire the coil differently and effect rotor phasing.

The camshaft valve timing has to be checked with a degree wheel when assembled. What aftermarket camshaft are you using?

[Mark E.]

Re: Strange timing issue

[QUOTE=Terry Deusterman (11486);840474]Troy
If this does not let the vacuum can be in the right place they your distributor is off a tooth or two, and it does make a difference./QUOTE]

Guys, think about it.

It makes no difference how the distributor is clocked or how the cables are oriented in the cap (as long as they remain in firing order sequence). Engine timing can be set to factory specs with the distributor housing reclocked in any position relative to the intake. Yes, some orientations are not physically possible because of interfere between the distributor and various engine parts.

What matters is the position of the distributor's cam relative to the ignition points. That's what determines timing.

Troy, To Duke's point, make sure you're measuring initial timing at a slow enough rpm to ensure the centrifugal advance hasn't started.

Then check to ensure the dimple on the distributor gear is aligned with the rotor tip.

After that, mechanically check piston TDC to verify accuracy of the timing marks.

[Duke W.]

Re: Strange timing issue

On some small block engine configs, there may be more than one acceptable installation position, and the orientation of the dimple in the drive gear may be of no consequence, however, on Corvette engines there is only ONE that will allow you to get the initial timing in the proper range without the VAC interfering with the manifold or coil/wire bracket.

The proper wire indexing and installation instructions are in all the service manuals with the exception that they make NO REFERENCE TO THE DIMPLE ORIENTATION. (I figured this out back in 1965. On my third try to install the dist. properly, I noticed the dimple. It was a Eureka moment.) With proper gear orientation (gear dimple pointing the same direction as the rotor tip), dist. installation angle, and the timing in the proper range, the dist. window should be approximately normal to engine centerline. If not, there I likely something wrong with the configuration/installation.

There is evidence that some aftermarket cams don't have the distributor drive gear properly oriented on the camshaft and the dist. gear may have to be installed with the dimple pointing opposite the rotor tip. However, I'm surprised this would be the case for a Federal Mogul cam. AFAIK the are all manufactured to the GM blueprints.

I've also heard reports that some aftermarket dist. gears have no dimple.

Duke

[Gene M.]

Re: Strange timing issue

For years now I've been befuddled about the ignition timing on my 63 fuelie. To get it to idle and run reasonably it takes way more advance than specified. When I say way more I mean like 30 degrees at idle with the vacuum advance line blocked off! I've just discovered the same issue with the newly rebuilt 265 V8 in my 55. I don't get it. What is going on?

I don't live at altitude, maybe 2500 feet.

Since two cars exhibit the same strange behavior I thought maybe my timing light was screwed up. So I bought another one and got the same results. Double checked to make sure I hooked it to the correct spark plug wire too.

On my 63 I thought maybe the harmonic balancer had slipped. Also thought maybe I have the wrong timing cover and the timing tab is in the wrong place. Doesn't seem like either and very odd that I now have another engine doing the same.


Any ideas?

Initial timing at 30 degrees on top of vacuum advance not to speed of centrifugal is crazy. Piston knock has to be obseen. I suggest it makes no difference how the distributor is set relative to correct position. As long as #1 is triggered at the time of #1 piston.

You have an incorrect indication of when the pulse is triggered. Be it hardware or the instrument. I propose it is nothing in the initial 30 degree range, as it would not run right as suggested.

Be sure you have correct hardware for two engines you are saying are initial set to 30 degrees. Something is not right.

[Bill S.]

Re: Strange timing issue

Has the vibration dampner slipped? If the engine idles correctly and and you timed it properly and the marks don't line up then maybe the balancer has slipped. It happens. Your old one can be rebuilt.

[Troy P.]

Re: Strange timing issue

I considered the balancer slipped issue years ago as a possibility on my 63. But now I have a 55 with the same timing issue. What are the odds of that being caused by a balancer.

[Richard G.]

Re: Strange timing issue

Troy;
If it is possible it will need to be confirmed it isn't the issue.
I have found as soon as one mentally says "its unlikely or impossible" I have upped the odds exponentially that that is the issue!

Do you have the fined balancer installed? This balancer was only manufactured with the correct key to timing mark orientation for your car.
Is the timing mark lined up with the key in the balancer. If this is off, as far as you indicated, you may be able to confirm the orientation visually.
Rick