Ping Ping Ping
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 801
Likes: 17
From: Middletown Delaware
Ping Ping Ping
I have a stock 79 that wont stop pinging. I have lars paper and think I have problem figure out just need opinion. OK mechanical set at 19 idle and 32 at max right now a little low .Vacuum advanced at 33 idle and 45 max I am hooked up to full vacuum. I have heavy springs in distrub and dist has been gone over and repaired. Vacuum can pulling 13 degrees so this is not my problem.Ok it idles rough with vacuum attached and much better with advance diconnected. I think my next step is to try ported vacuum. I read some post that stated some engines like ported vacuum better. Ok I will try this any help on what port to move it to on rotchester would be nice. Or any other advice.Dave
Safety Car
Joined: Oct 2005
Posts: 3,570
Likes: 1
From: Algonac Michigan
I think you may have too much initial advance.
I have mine set at 16* initial with vac disconnected.
At 2500 rpm I get my full timing in and have 36* advance.
You really don't have to be concerened with initial timing at idle. That will take care of itself after you get the rest of the timing right.
So too much initial and maybe too heavy of springs to get your 36* at 2500 rpm IMHO.
Good luck
I have mine set at 16* initial with vac disconnected.
At 2500 rpm I get my full timing in and have 36* advance.
You really don't have to be concerened with initial timing at idle. That will take care of itself after you get the rest of the timing right.
So too much initial and maybe too heavy of springs to get your 36* at 2500 rpm IMHO.
Good luck
Instructor
Joined: Jun 2006
Posts: 123
Likes: 0
From: Westminster MD
I had the same problems as you, I gave up on vacuum advance and just ran with it disconected. But I still had a rattle everytime I stepped on it (thought it was the manual choke cable hitting the air filter base - I was wrong). It turned out that the timing mark my car was tuned to was wrong. The harmonic balancer had two marks about 38-40 degrees apart. I bought a piston TDC stop (SUM-900189) from Summit for $6.95 and determined exactly where TDC was and it wasn't where it was tuned to. So I re-tuned it to the correct mark and what a difference. After setting the total timing to 36 degrees I reattached the vacuum advance and yes the engine ran faster instead or worse. Now I can run it with no rattles or pings (I was able to run a 0 to 60MPH in 5.7 seconds, what a difference).
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 801
Likes: 17
From: Middletown Delaware
Well I messed with the timing today and I see what the problem is but not sure how to fix it short of replacing Dist. The mech. timing is only advancing 13 degrees. So when I set max to 36 my idle is at 23 degrees which works till I plug in vacuum can and it goes to 37 at idle. Wow What should I look for to repair mech advance. Dave
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Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
Initial timing should be between 4 and 8° BTDC. Sometimes more, but that is a save starting point. Total advance should not exceed more than about 36° and put it fairly late in the rpm band to start with (selecting the right spring) something like 4000 rpm. Hook up the vacuum advance and see what happens.
If you still have ping with these settings, i would indeed check your timing mark. sometimes they are indeed off.
If it doesn't ping you can step up, meaning you can bring in your advance slowly to an earlier point in the rpm band, but in any advent, not any lower than 2500. If it still doesn't ping, you can gradually put in more initial advance.
But be carefull, a ping is not always audible... If you want to stay on the safe side, do not go over 10° initial and all in at 3000 rpm.
If you still have ping with these settings, i would indeed check your timing mark. sometimes they are indeed off.
If it doesn't ping you can step up, meaning you can bring in your advance slowly to an earlier point in the rpm band, but in any advent, not any lower than 2500. If it still doesn't ping, you can gradually put in more initial advance.
But be carefull, a ping is not always audible... If you want to stay on the safe side, do not go over 10° initial and all in at 3000 rpm.
Instructor
Joined: Dec 2006
Posts: 207
Likes: 0
From: Keller TX
Well I messed with the timing today and I see what the problem is but not sure how to fix it short of replacing Dist. The mech. timing is only advancing 13 degrees. So when I set max to 36 my idle is at 23 degrees which works till I plug in vacuum can and it goes to 37 at idle. Wow What should I look for to repair mech advance. Dave
Do you have an agressive cam?
I also have the rough idle with an agressive cam on my rebuild. Can't get a smooth idle in gear with the 16 initial, 36 all in at 2500 and 52 total. According to Lars, I need to run 22-23 inital and 'limit' my mechanical advance to make sure I stay at the 36 all in. Then....I need to use a Ported vacuum.
He said that a significant cam needs more initial in order to get the idle in gear and idle in park to be friends.
I haven't had time to do this yet but hope to work on it this weekend. Maybe you just need to go with the 36 all in and make sure you are not more than 52 total with a ported vac and see if that helps.
Again...I'm far from an expert...just passing along info that I received.
Good luck,
Doug
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
Dave all stock GM hei units have 20* mech. check for a limiting bushing in the dist. if not there is something wrong with the advance mech.
Take the cap and rotor out and look close see if the weights are resting in the correct spot.
Spin the shaft with your hand see if it is free to spin with no binding.
Set initial at 8* to 10* with vacuum disconected.
Neal
Take the cap and rotor out and look close see if the weights are resting in the correct spot.
Spin the shaft with your hand see if it is free to spin with no binding.
Set initial at 8* to 10* with vacuum disconected.
Neal
Last edited by chevymans 77; Aug 19, 2007 at 07:49 PM.