55 Degrees Initial Timing.... Huh? - Page 2 - Chevy Nova Forum
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Old 16th-September-2019, 05:51 PM   #16
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Ignition Module

BHJ just got back to Sparky and they said if TDC matches the pointer we are good. Is there any chance the ignition module is bad? I guess that still does not explain the 55 degrees. I think I will loan him my timing light and see what that shows. I am still of the mindset no way it's actually at 55.
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Old 16th-September-2019, 09:01 PM   #17
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As said the TDC mark on a 68 and earlier balancer is in line with the keyway. On a 69 and later balancer it's 10 CCW from the keyway. If you use the 68 and earlier timing tab, you'll indicate 10 more ignition advance than you really have.

There is also a fairly rare 350 balancer that has the TDC mark 30 CCW from the keyway.

I do not trust any dial back timing light except for the really high end ones like Snap On. A timing tape works well in place of a degreed balancer and is really cheap.

Cam timing does NOT affect ignition timing mechanically. That said with that big cam you'll need to run a lot of timing at low speeds.

A borescope can only be trusted to within maybe +/-5 on a good day. Use a piston stop or dial indicator.
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Old 19th-September-2019, 11:19 PM   #18
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I think I am slated to go back over to Sparky's this weekend to see what we can find out. I will take my timing light and see if I can find my piston stop (I think it's hiding with the bushings for my degree wheel). I am also going to check that the vacuum and mechanical advance are not stuck. I was thinking even if it is the wrong balancer, I would still only be off 11 degrees, which still has us well over 40 initial. We will see what we can come up with. If I know Sparky, he won't lose any sleep over it, if it runs well, it's on to the next project. I will report back either way.
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Old 21st-September-2019, 12:23 AM   #19
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I just noticed that you are using a Speedway HEI.
I suggest removing the cap and confirming the the distributor's centerplate is installed correctly.

Below is a diagram for the correct orientation of the weights and centerplate for a clockwise rotating engine.

Notice that the pointy part of the weights rest on the rounded part of the centerplate (Springs were removed for photography).

If the centerplate is installed upside-down, the weights will have a "sloppy" fit against the centerplate (even with the return springs installed) and could advance the timing at idle due to the centrifugal force.
I had a similar experience with a Pertronix HEI a couple years ago. I had a very high/erratic initial timing at idle due to my centerplate being installed upside-down from the factory. Once I flipped the centerplate, all of my "mysterious" timing issues were solved.

I would also check the timing light you are using on an other engine with a "Known" initial timing number to check the accuracy of your timing light.
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Old 21st-September-2019, 01:39 PM   #20
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11 inches of vacuum is low if the cam is mild. that said, I would want to do a test first, to confirm or deny issues from the cam being off a tooth retarded.

Do a full engine compression test, all plugs out, throttle wide open. Extremely low readings will indicate the intake valve is closing way too late, cam retarded a tooth. This will give low vacuum readings, love extremely high timing numbers, have bad low end power, fair to good top end power.

Doing this will get the test done, and either show a problem, or not.

From the picture, the vacuum advance does not have any degrees stop in place, and being that way, is probably capable of making 25 to 30 degrees of timing, if the vacuum is enough to run the pull pin through its full travel.

I would want to see just how many degrees the initial is, with the vac adv disconnected, then, add the advance to full manifold vacuum, and see how many degrees comes up from it. To a point, the more IDLE degrees, the better the idle vacuum reading should get to, but, there is a reasonable limit of IDLE timing, 22 to 24 degrees, no more. Example: 14 INITIAL, add 10 by vacuum advance on full manifold vacuum, IDLE, 24.

A simple stop can be affixed to the vacuum advance to get to the right idle timing number.
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Old 21st-September-2019, 08:57 PM   #21
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Quote:
Originally Posted by Old Man View Post
From the picture, the vacuum advance does not have any degrees stop in place, and being that way, is probably capable of making 25 to 30 degrees of timing, if the vacuum is enough to run the pull pin through its full travel.
A simple stop can be affixed to the vacuum advance to get to the right idle timing number.
I agree... a Vacuum Advance Stop Plate is an important component to have when dialing in your timing curve. The photo I posted earlier was a spare HEI that I use for photography purposes and the picture was taken just to reference the correct installation/orientation of the centerplate and advance weights for the OP to look at in their Chevy HEI.

For my HEI set-up, I do use a Vacuum Advance Stop Plate set to limit the vacuum advance to 11 during full pull at idle. (shown in the photo below) Vacuum advance is connected to a full time vacuum source.
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Last edited by RifRaf; 23rd-September-2019 at 07:01 PM.
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Old 21st-September-2019, 09:26 PM   #22
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It looks like I will be going over to spend a little time working on this and some other issues. I have a lot of things to look at. Though we have to get it tracking straight or the test drives will kill us.

Thanks for all the advise, I will report back on what I find.
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Old 22nd-September-2019, 01:01 PM   #23
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Ah, yup, the much too complicated MSD vacuum advance degrees stop, way too complicated. The Crane 99619-1 stand alone adjustable degrees stop is far easier, and more accurate than this one is.

Anyone that wants the instructions, please ask for them, they are FREE.

gmvacuum
advancemodifications
gmail

Last edited by Old Man; 22nd-September-2019 at 01:05 PM.
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Old 22nd-September-2019, 11:11 PM   #24
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Today's update

We didn't get much time working on the tune today, but in between other projects on the car I did a couple checks. 1. Vacuum advance is working normall (though not using it at the moment for obvious reasons). 2. Mechanical advance working normal, not sure how many degrees it's giving, my advance light does not go that high. 3. Confirmed timing with a second timing light. 4. Got almost 200 psi compression, just tested one cylinder to make sure it wasn't super low. 5. Dug up a picture on my phone when we were putting to motor together and I did set it straight up. Checked another picture from when the engine was originally built by a very reputable shop, it had a belt drive on it, we took off, he had it set up straight up too. 6. Changed the power valve to a 4.5, and not sure why but we found detonation at about 2/3 throttle where we didn't have any before.

It's gonna be a couple weeks before we can take a look again. So any feedback or thoughts would be helpful. Since we have detonation now, we can start backing timing off, but we lose a few inches of vacuum, so we may need a 3.5 pv.

Thank you everyone for suggestions. Keep them coming. I know a lot of people say to degree the cam, that will be last resort if we can't get anything else figured out.
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Old 23rd-September-2019, 07:37 PM   #25
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You're probably getting detonation because you have over 10:1 compression with iron heads. Unless you are running higher octane race gas. Are you running flat tops or domed pistons? If doomed, that isn't helping any. You also may need a colder spark plug.
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Old 23rd-September-2019, 08:02 PM   #26
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200 is good c/r, cam doesn't sound retarded, good.

Leaving the vacuum advance disconnected helps NOTHING. Not having it set up for the correct degrees helps NOTHING.

Using a dial back timing light on that type system helps NOTHING. Degree tape on the balancer, leave the dial back off.

Now, INITIAL timing IS????
VACUUM ADVANCE degrees timing IS????
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Old 6th-October-2019, 06:45 PM   #27
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Any update here?
We're waiting...
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Old 9th-October-2019, 11:00 PM   #28
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Sorry

Update:

No update, we have not had a chance to take a look, him on vacation, me burst pipe in the house. We are planning on getting some time this weekend. The current plant is to pull the dampener put the degree wheel on the crank, use the piston stop to find true TDC. Get it on TDC and verify the balancer mark. If it's right, the front cover comes off for more investigation, if it's wrong, mark it correctly and call it a day.

Stay tuned.
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Old 10th-October-2019, 05:16 PM   #29
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I hope this picture loads, it shows a much easier stop for the vacuum advance degrees stop plate, adjustable in 2 degree increments per notch. It does require drilling and tapping the vacuum advance mounting plate with one hole to mount the plate.

Also, with the stop in the first picture, the MSD stop, it uses a long screw through one of the vacuum advance screw holes. IF that screw hole in the body is weak, it could strip easily, and need an insert to hold both the end of the vacuum advance, and the stop in place, while the one in the lower picture is held in place by a separate drilled and tapped 8/32 stainless steel hex head hardware store screw and flat washer, threaded into the much stronger steel vacuum advance mounting bracket. Under a buck for both screw and washer, stop plate is about 3 bucks at speed shops, online speed shops, Ebay.

EITHER WAY WORKS, AND IS NEEDED.

EDIT: good heavens, it loaded the picture, it worked, amazing, first one I ever did. I'm verklempt!
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Last edited by Old Man; 10th-October-2019 at 05:28 PM.
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Old 11th-October-2019, 11:07 PM   #30
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I think it's good news?

So, we confirmed TDC with a piston stop. To be honest I was hoping it was off. But it appears that our 55 degrees is accurate. Last visit we made some big carb adjustments and got it running a little better down low, but found major detonation over 2500 which we had never had before. I think we will take another crack at backing the timing down significantly, and see what we find. I know we are kind of swimming upstream with this big of a carb.

Hopefully another update tomorrow. Thanks for all the help.
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