Erratic Timing on 472

Brother_B · #1 (**permalink**) 02-11-07, 03:34 PM

I tried to set my timing. The timing mark was jumping around all over the place. I mean A LOT, not just dancing around near the notches. I mean it was jumping everywhere visible on the pulley, and probably was on the far side of the pulley when the light flashed, at times. What can cause this?

I have the points-style distributor. I did have the vacuum advance disconnected while trying to set timing. So far my guesses are timing chain, or bad plug wires, or I have spark jumping around in the distributor, or some kind of interference picked up by the inductive pickup on the timing light.

Engine is running rough, very difficult cold-starting. I recently replaced the carburetor, so that is partially responible for the roughness. I want to set the timing before I make final adjustments to the carb.

Any help appreciated! Thanks, B

The Ape Man · #2 (**permalink**) 02-11-07, 05:36 PM

Check all primary ignition wiring connections. Borrow a diferent timing light. Try another set of points and condensor. Make sure mechanical advance works properly. A bad timing chain might make the flicker wander a little but not like you have described IMHO.

ja70cad · #3 (**permalink**) 02-14-07, 01:37 AM

I would seriously take a look at your timing chain, especially if it's never been changed... Believe me, I learned the hard way!! The old timing gears were made of nylon and once they begin falling part, watch out! You can sometimes see the pieces of nylon in the oil too.

Good Luck, Bro...

BodybyFisher · #4 (**permalink**) 02-14-07, 08:34 PM

Quote:

Originally Posted by ja70cad

I would seriously take a look at your timing chain, especially if it's never been changed... Believe me, I learned the hard way!! The old timing gears were made of nylon and once they begin falling part, watch out! You can sometimes see the pieces of nylon in the oil too.

Good Luck, Bro...

Good advice, I have changed them on 390, 429 and 472 caddy engines I was always amazed that they were fiber.

If that is not your problem check the distributor gear and the bushing near the points. I have seen this problem in a 429, but I cant recall if it affected the timing or the dwell.. Also check the centrifical advance for the springs...they springs may be weak, and check the vacuum advance for leaks..

Brother_B · #5 (**permalink**) 02-22-07, 12:59 AM

Thanks everybody for the input. I replaced plug wires and points/condenser. Once I replaced the points/condenser, it wouldn't run anymore. I was unsuccessful setting the point gap / dwell. (Gap measurement was difficult with my set-up, and the car needs to be running to set dwell.) So I decided to go ahead with the HEI distributor - I was going to anyway. I ordered one, and am waiting for it to get here. I hope that will fix all my problems (?). Next project may be a timing chain. I am hoping that at least the new distributor will allow me to actually read the timing clearly. Thanks again for the input, and I'll let you know what happens.

Now I just need to figure out which wire will give me 12V. Maybe the new distributor will come with good instructions.

Thanks again for helping out a noob.

BodybyFisher · #6 (**permalink**) 02-24-07, 05:36 PM

Make your job easier by bringing your #1 up to TDC and mark the position of the body of your distributor and mark where the ROTOR is pointing so that you get it back in relatively the same place.....

Sasquatch · #7 (**permalink**) 02-27-07, 09:23 AM

Check out this link it will tell you all you need to know. I changed my 1969 472 Cadillac Hearse to an HEI from a 74 Caddy and love it. Pay particular attention to tip #2. A relatively cheap part that made a huge difference as far as detonation (pinging). Also when possible run premium. Here's the link.

http://www.oldengine.org/unfaq/hei.htm

Brother_B · #8 (**permalink**) 02-27-07, 11:53 PM

Thanks Sasquatch. That's funny, I had just found your link this morning looking for good info on how to replace the resistor wire. I am feeling pretty good about the wiring part now. I received my DUI HEI distributor yesterday, and tried to make this swap this evening. First snag: My old distributor refuses to come off! I guess it's just been on there so long that gasket has glued it on? Or maybe it was installed with no gasket and it's rusted on? What the heck? I am trying to devise some kind of puller. (I guess they actually make them, I have discovered.)

Regarding Tip #2, looks like I have a 15* vacuum advance can.

Which brings me to my next question, for anyone that might still be reading this thread: I am very curious about Thought #1 at Sasquatch's link: Manifold vs. Ported vacuum for vacuum advance. Any thoughts? Vehement opinions? Straight-up knowledge? If I use manifold vacuum for advance, do I need to change vacuum cans? I have read some persuasive arguments for using manifold vacuum for advance. Here's one link:

http://www.hotrodders.com/forum/dist...1-a-59033.html

B