Knocking and Pinging

Anything Corvair related
User avatar
eForce
Posts: 111
Joined: Sat Jan 18, 2014 5:43 am

Knocking and Pinging

Post by eForce »

Hi guys. Finished replacing the head on the drivers side. Got the motor built and reinstalled. Runs WAY better than before. As long as it's cold. The problem is, once it warms up AND I'm at idle in drive, it knocks and pings like crazy. Once I give it a little gas, it runs great again.

Any ideas? I've played with the timing, carbs and checked for vacuum leaks.
User avatar
terribleted
Posts: 4588
Joined: Sun Apr 18, 2010 2:36 pm
Location: Atlanta, GA
Contact:

Re: Knocking and Pinging

Post by terribleted »

play with them some more and also check idle speed. This symptom in a powerglide is usually timing and rpm related
Last edited by terribleted on Tue Apr 18, 2017 5:40 pm, edited 1 time in total.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia
User avatar
eForce
Posts: 111
Joined: Sat Jan 18, 2014 5:43 am

Re: Knocking and Pinging

Post by eForce »

agreed but why would it run so great with no knocks when it's cold?
Jerry Whitt
Posts: 887
Joined: Thu Sep 26, 2013 2:42 pm

Re: Knocking and Pinging

Post by Jerry Whitt »

What is different when cold?

The most common difference is the chokes are nearly closed and the fast idle is holding a much higher idle speed. The means there is a much richer mixture when cold. The rich mixture will hold off the pinging or knocking.

You noted that when accelerated, runs better. Sounds like the hose to the vacuum advance is hooked up to intake manifold vacuum and the choke pull off is hooked to the spark port. Recheck.

Timing is critical, of course, and an error in setting or a bad harmonic balancer could cause these symptoms.
Jerry Whitt
ASE CERTIFIED MASTER TECHNICIAN
Retired
Hemet, Callifornia
65 Monza, purchased new
65 Corsa convertible
66vairguy
Posts: 4531
Joined: Tue Dec 21, 2010 3:44 pm

Re: Knocking and Pinging

Post by 66vairguy »

Back to basics. Check the static timing at the specified RPM and make sure the vacuum advance is disconnected until after you set the timing.

Another mistake folks make is they hook the distributor vacuum advance to the wrong carburetor port so the vacuum advance goes full on (should be little or no vacuum at idle using the correct port).
User avatar
eForce
Posts: 111
Joined: Sat Jan 18, 2014 5:43 am

Re: Knocking and Pinging

Post by eForce »

ok so I set the timing properly. It was out a bit but not much. 2ndly I adjusted my chokes. Still knocked when it warmed up. My vacuum advance is hooked up to the top port so I tested it and my vacuum was at 9. I then tested the bottom port and that was 10 so I moved the vacuum advance to that port and that seemed to resolve it. Is that the right port?

Now it stumbles a bit intermittently but I'm certain that's my chokes.
66vairguy
Posts: 4531
Joined: Tue Dec 21, 2010 3:44 pm

Re: Knocking and Pinging

Post by 66vairguy »

There are two vacuum ports near the base. The horizontal tube port goes to the choke pull off module. The vertical tube port goes to the distributor advance canister. Since BOTH carburetors have these two port and only ONE vacuum hose goes to the distributor, the other carburetor should have a rubber cap on the unused vertical tube port. If the engine is properly tuned there should be little or no vacuum at the vertical tube port at idle, but vacuum as the throttle is opened. When the carburetors are at fast idle (choke on) the throttle plate is open enough so you will see vacuum at the vertical tube port. You will ALWAYS see vacuum at the horizontal tube port to the choke pull off when the engine runs.

This is based on a properly tuned engine with no issues. Have you balanced the two carburetors at idle with a tool like a Uni-Sync?
User avatar
bbodie52
Corvair of the Month
Corvair of the Month
Posts: 11872
Joined: Mon Aug 06, 2012 12:33 pm
Location: Lake Chatuge Hayesville, NC
Contact:

Re: Knocking and Pinging

Post by bbodie52 »

:goodpost: Here are a couple of illustrations that might help by supporting the above explanation...

Image

Image
A UniSyn gauge measure air flow volume through the throat of each carburetor. It is an effective method of synchronizing multiple carburetors, and can help to ensure even matched airflow at idle and at open throttle. It is one aspect of the engine tuning process.

You want a balanced pair of carburetors that are both clean and equal, and balanced for airflow at idle and at part throttle. A Unisyn air flow gauge is an inexpensive tool that helps to accomplish this. The following Corvair Forum link will provide you with a description of the function and use of a Unisyn gauge:
:link:viewtopic.php?f=55&t=5922&p=40585&hilit=air+flow#p40585
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
64powerglide
Posts: 1604
Joined: Tue Mar 25, 2014 9:18 pm
Location: Kalamazoo Mi..

Re: Knocking and Pinging

Post by 64powerglide »

I have yet to see what your timing light says about your timing, you say you set it properly which is what when the engine is hot????? It should be 12 or 13 BTDC at 500RPM in drive with the vacuum hose off & plugged. If you have everything set right & you still get knocking & pinging your low band in the trans might need to be set. I had my 64 low band adjusted last year by a good Corvair trans guy & now it doesn't want to stall when I come to a stop.
64Powerglide, Jeff Phillips

Kalamazoo, Mi..
User avatar
terribleted
Posts: 4588
Joined: Sun Apr 18, 2010 2:36 pm
Location: Atlanta, GA
Contact:

Re: Knocking and Pinging

Post by terribleted »

You say 9-10 " of HG at idle is your vacuum reading? That is way low. Vacuum at idle in a good engine should be 17-21". Causes might be a vacuum leak (do the balance tube hoses seal on both sides? Is the extra vacuum port on the left carb blocked off. Do the carbs use mounting gasket, spacer, gasket on both sides? Low compression can cause low vacuum. Improper valve adjustment can cause low vacuum and quite noisy pinging type sounds. I would make sure I have no vacuum leaks and then I would re-adjust the valves. It is very possible you have had a lifter or lifters pump up that are now holding the valves slightly open leaking compression. When they are like this when you accelerate the engine the symptom can smooth out since the time the leaking is happening is minimized. Have you tested compression? You would likely see this issue on a compression test.

Here is a link I found to vacuum testing of engines http://www.gregsengine.com/using-a-vacuum-gauge.html
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia
User avatar
eForce
Posts: 111
Joined: Sat Jan 18, 2014 5:43 am

Re: Knocking and Pinging

Post by eForce »

Yes, I looked that up and put the vacuum advance back on the vertical port. I got vacuum up to 11 with curb idle. Compression is 150. Timing is at 10 deg. If I go more...the knocking comes back.

I did replace the wires because I seemed to have a weak spark. That helped out quite a bit but now I've messed up my carbs and needs to be synced again.

Problem MIGHT be solved. The carbs were rebuilt a couple years ago. but the drivers side seems to be a very weak squirt compared to the passenger side. I have the chokes completely disconnected right now.
64powerglide
Posts: 1604
Joined: Tue Mar 25, 2014 9:18 pm
Location: Kalamazoo Mi..

Re: Knocking and Pinging

Post by 64powerglide »

I'm running my 64 110 at 14 BTDC, I had it at 16 but was getting spark knock at 60 to 70 MPH so I backed it off to 14. I'm running 87 octane fuel. If you can't get it to run good when it's over 10 degrees advanced something else is wrong. :my02:
64Powerglide, Jeff Phillips

Kalamazoo, Mi..
User avatar
terribleted
Posts: 4588
Joined: Sun Apr 18, 2010 2:36 pm
Location: Atlanta, GA
Contact:

Re: Knocking and Pinging

Post by terribleted »

The accelerating fuel squirt is not particularly relevant to your issue. If one carb draws way more air than the other at idle that is very possibly related. You may have a plugged up carb. So let me get this right you rebuilt the engine and did not go thru the carbs? Go thru both carb immediately, reset all tolerances, make sure all passages are clear and ensure both draw evenly at idle and are balanced to each other. See how the car is at that point. If still doing similar stuff I would doing a running valve adjustment, adjusting to 3/8- 1 of a turn of pre-load if the lifters will take 1 turn in without misfire. Your vacuum readings are still 30% or more low Indicating low compression, big vacuum leak, or bad valve adjustment (perhaps a dead carb could make similar vacuum readings? A dead carb can certainly make the car knock and ping under load.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia
User avatar
eForce
Posts: 111
Joined: Sat Jan 18, 2014 5:43 am

Re: Knocking and Pinging

Post by eForce »

Update...I pulled carbs and reassembled with a basic starting point for syncronization. I also replaced the O-Rings on my push rod tubes as they leaked when it got hot. I noticed that I had 3 push rods in backwards. Interesting, however, knocking and pinging is gone. Not sure if the push rods had anything to do with it....could also have been a bad seal on the carb base. I dunno but it's fixed.
User avatar
terribleted
Posts: 4588
Joined: Sun Apr 18, 2010 2:36 pm
Location: Atlanta, GA
Contact:

Re: Knocking and Pinging

Post by terribleted »

Well you either fixed a carb (or carbs) or your valve adjustment is no longer faulty after re-adjusting during pushrod tube re-sea.l
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia
cnicol
Posts: 546
Joined: Wed Jan 20, 2010 8:11 pm

Re: Knocking and Pinging

Post by cnicol »

eforce wrote: "...and reassembled with a basic starting point for syncronization."

Craig repiles: Proper sync. or carb base gasket leak repair is probably what fixed the problem

It was obvious to me that your carb sync was way off because the upper vacuum port should be "zero" vacuum, idling after warm up. The fact that you measured 9" there indicates the carb throttle plate was not at idle but instead fairly open (which exposes the hole that leads to the vacuum pipe). Carbs were way out of sync. You got the sync. right so vacuum port went to "0", unintended vacuum advance went away and all is well. Yeah!
'61 140 PG Rampside
'66 Rear Alum V8 4-dr
'60 Monza PG coupe (sold, sniff, sniff)
'66 Corsa Fitch Sprint Conv. (First car 1971, recently repurchased)
Post Reply

Return to “Corvair Talk”