pinging under light load - Page 4 - Chevelle Tech
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post #46 of 53 (permalink) Old Dec 29th, 19, 11:17 AM Thread Starter
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Re: pinging under light load

I am reasonably convinced that my ignition is not at fault so will start a new thread elsewhere
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post #47 of 53 (permalink) Old Jul 25th, 20, 12:12 PM Thread Starter
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Re: pinging under light load

I should have verified my timing mark was correct, I had painted what I thought was the timing mark with white paint, it turned out that because I didnt have my reading glasses on I marked the wrong place, to confuse the matter the holley carb had a faulty metering block, air bleed on one side was oversized giving me lean plugs, it wasnt the lean condition causing the pinging it was the goofed up timing, after much messing about I went back to basics with a piston stop, the metering block was a little harder to diagnose, I had that off dozens of times before I noticed the oversized air bleed, I hope my mistakes are a help to others. It was a fresh build, I thought I was looking for one fault not realising that there was two faults.
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post #48 of 53 (permalink) Old Jul 25th, 20, 1:42 PM
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Re: pinging under light load

Glad to hear it was resolved and you took the time to update this thread!
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post #49 of 53 (permalink) Old Jul 25th, 20, 2:08 PM
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Re: pinging under light load

Quote:
Originally Posted by ivorchevelle View Post
I was hoping to come back with good news, the plugs which are fed from the passenger side plenum of the dual plane manifold are still much leaner looking than the rest, #5 is pure white.
As #5 is the leanest by far I assumed that any vacuum leak is nearest to that cylinder, as I have just swapped the gaskets I thought I would test it, I fitted a plate on the manifold with an air line fitting in it, took off the valve rockers and connected the airline at about 10 psi and listened for the leaks, this proved inconclusive so I connected it to my vacuum pump, I pumped it up to 12 inches and it held pretty good, it took about 30 minutes to leak down, I am now thinking it is an issue with the carburettor, passenger side as cylinders 2,8,3 and 5 are leaner than the rest, blocked orifice ? Maybe the valve on #5 does not operate correctly when the engine is running, thus causing the other cylinders that share the same plenum to indicate lean also. The photo is plug #7, 5 and 3 from left to right
Those white plugs sitting right next to plugs that are almost normal looking plugs are a classic picture of lean cylinders V. good cylinders plugs.Its great that you figured it out and just as great is that you posted back saying you fixed it.

Quote:
Originally Posted by ivorchevelle View Post
I am reasonably convinced that my ignition is not at fault so will start a new thread elsewhere
Quote:
Originally Posted by ivorchevelle View Post
I should have verified my timing mark was correct, I had painted what I thought was the timing mark with white paint, it turned out that because I didnt have my reading glasses on I marked the wrong place, to confuse the matter the holley carb had a faulty metering block, air bleed on one side was oversized giving me lean plugs, it wasnt the lean condition causing the pinging it was the goofed up timing, after much messing about I went back to basics with a piston stop, the metering block was a little harder to diagnose, I had that off dozens of times before I noticed the oversized air bleed, I hope my mistakes are a help to others. It was a fresh build, I thought I was looking for one fault not realising that there was two faults.
I have a question about your balancer. About the balancer was the area that you painted and confused for the TDC mark a wide 1/8th inch cut in the outer ring of the balancer ?

John
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"Quality is always remembered,long after the price is forgotten"
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post #50 of 53 (permalink) Old Aug 1st, 20, 9:25 AM Thread Starter
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Re: pinging under light load

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Originally Posted by 71350SS View Post
Those white plugs sitting right next to plugs that are almost normal looking plugs are a classic picture of lean cylinders V. good cylinders plugs.Its great that you figured it out and just as great is that you posted back saying you fixed it.





I have a question about your balancer. About the balancer was the area that you painted and confused for the TDC mark a wide 1/8th inch cut in the outer ring of the balancer ?
It was basically a scratch in the black coating of the balancer, it was dead straight and in poor light without my reading glasses on I crawled under the car and painted it with tippex by mistake. I hope this thread helps others, this forum has been very helpful to me.
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post #51 of 53 (permalink) Old Aug 1st, 20, 1:33 PM
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Re: pinging under light load

Quietly reading, and I have a question, what type intake manifold is in place (sorry if I missed it in the topic), single, or dual plane?

Of course, a single plenum design will have all plugs fed by both barrel sides of the carb.

A dual plenum design would have two specific paths, one for cylinders 1, 4, 6, 7, fed frm one side of the carb, the other would be 2, 3, 5, 7 with the other side of the carb.

You mentioned a different primary air bleed per side of the carb, does it show different readings for the two sides, or only single different plugs, at random?


One of the things I used to do when I worked for Holley was to remove the set size air corrector's and bottom thread the holes, then use Allen set screws drilled to size in their place, so I could easily replace, and make my own air corrector jets.
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post #52 of 53 (permalink) Old Aug 1st, 20, 2:38 PM
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Re: pinging under light load

How big of a timing error did the mistake with the damper cause?

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post #53 of 53 (permalink) Old Aug 2nd, 20, 12:48 PM
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Re: pinging under light load

Please remember, the dampener outer ring can slip and cause timing anomalies, and, there are a number of different timing scales for the various engines used over the years, three at the driver side 2:00 positions, one at the noon position behind the water pump, and yet another on the bottom of the pan, at 6:00 for motor homes, etc.

You should have it dialed in now, doing the piston stop to confirm TDC on the dampener.

Don't forget to take a very close look at the back of the dampener as you hand turn the engine over (I do it from the underside of the engine), to see if the Elastomer bonding is good between the outer ring and inner hub on the dampener.
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