C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Timing question

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Old Aug 25, 2025 | 01:18 PM
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Default Timing question

Hello all!

Ive been dealing with some pinging on acceleration in my 86 that i suspect is due to timing that is too far advanced. Last time I had the timing set I took it to a shop that deals with classics. I recently checked the timing (EST wire disconnected) and noticed that it was 6*BTDC in PARK while the sticker on my radiator cover states that it should be 6BTDC in drive. I wasn’t able to check the timing in drive since my parking brake isn’t working and I don’t have anyone to step on the brakes for me while i check the light. That being said. If the timing is set at spec in park is it the same in drive? Or would that cause the actual timing to be too far advanced?

Last edited by DJJ123; Aug 25, 2025 at 01:35 PM.
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Old Aug 25, 2025 | 02:09 PM
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Pretty sure with the plug disconnected it'll be locked at whatever the position of the distributor is regardless of rpm. The whole point of that thing being unplugged is so that the ecu can't change the timing, and there is no mechanical or vacuum advance so it is whatever it's set to till the ecu is involved again.
I'd run a tank of premium and see if the noise goes away first and then go from there.

Oh, this is all assuming your balancer ring hasn't slipped and the timing marks it's showing you are accurate.
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Old Aug 25, 2025 | 02:41 PM
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Originally Posted by wolf_walker
Pretty sure with the plug disconnected it'll be locked at whatever the position of the distributor is regardless of rpm. The whole point of that thing being unplugged is so that the ecu can't change the timing, and there is no mechanical or vacuum advance so it is whatever it's set to till the ecu is involved again.
I'd run a tank of premium and see if the noise goes away first and then go from there.

Oh, this is all assuming your balancer ring hasn't slipped and the timing marks it's showing you are accurate.
I see. I’m currently running 91 octane so I wouldn’t see why my fuel would be the problem. I’ve also thought about the issues being the harmonic balancer since i don’t know how old it is, but i don’t know how to tell if it’s slipped. Do you happen to know the procedure to check it?
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Old Aug 25, 2025 | 02:47 PM
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Basically you pull the spark plug on #1, stick something down there to touch the piston and roll the motor to the indicated TDC and see if the piston is in fact at TDC when the timing mark says it is.
There are tools for it and such, I usually use something long enough to reach in there but soft enough not to hurt anything, or break off. The balancer slipping is a thing that happens from time to time.
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Old Aug 25, 2025 | 03:42 PM
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Basically you pull the spark plug on #1, stick something down there to touch the piston and roll the motor to the indicated TDC and see if the piston is in fact at TDC when the timing mark says it is.

Don't forget, there are 2 times the #1 cylinder (all cylinders) comes to the top. Once when #1 is on compression stroke and once when it is on exhaust stroke. Don't forget to add that #1 should be pressurizing when it is coming up to true TDC. The crankshaft rotates twice 720° for each cylinder firing.
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Old Aug 25, 2025 | 05:52 PM
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Originally Posted by Vets-Vet
The crankshaft rotates twice 720° for each cylinder firing.
For checking the mark on the balancer vs piston position, it doesn't matter 'which' TDC #1 is on. In fact, you can use #6 cyl to check the mark if it is easier.

Last edited by IHBD; Aug 28, 2025 at 01:15 AM.
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