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Old 06-12-2019, 06:23 PM   #1
71CHEVYSHORTBED402
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What am I missing about ignition timing?

I replaced the chain and oil pump on a 402. The marks on timing gears are straight up 12 O-clock, and the harmonic balancer is dead-on zero. I think that means TDC to #1 (ha!). I reinstalled a Delco-Remy HEI. I didn’t mark anything, due to new paint and that, so like starting over I guess.

I turned the slot in the oil pump rod with a screw driver to approx. the #1 cylinder. Then set the distributor forward, marked the distributor where the front LH rotor will face the #1 cylinder, and spun the rotor to the marking.

From there I was able to mesh the gears very easily, goes straight in, but here is where I’m lost. After I mesh the gears, and as I lower it further into the gears - or more likely insert the distributor rod into the oil pump rod, the rotor swings clockwise to approx. straight forward.

Corrections welcome, but I think its right. Edit: The rotor must land on #1. Assuming it’s right, how come the initial rotor position (near forward) doesn’t screw things up? What am I missing?
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71 C10 Custom Deluxe, SWB, fleet, 402/400TH, A/C...Resource intensive......And (*^(*^ leaf springs. Speak of, looking for OEM rear sport bumper brackets for this ride. They're unlike those more common, even the outer brackets are different.

72 Cheyenne Super, LWB, fleet, C20, 402/400TH, A/C. Driver and tinker truck

Last edited by 71CHEVYSHORTBED402; 06-12-2019 at 08:29 PM.
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Old 06-12-2019, 06:55 PM   #2
truck-kid
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Re: What am I missing about ignition timing?

Sounds like you are engaged 1 tooth off as Rotor must point to #1 when fully engaged.Remove distributor and turn oil pump driveshaft counter clockwise slightly untill you can drop distributor in and it points towards #1 on the cap. You can verify correct position when your done by with #1 plug out turn engine over by having someone bump starter or turn over by hand untill #1 just starts to build compression then continue turning by hand till tdc marks align on balancer and timing tab.The rotor should point to #1 on the cap.
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Old 06-12-2019, 07:19 PM   #3
garyd1961
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Re: What am I missing about ignition timing?

Set your distributor in the hole but don't engage the gears. Turn the rotor to the correct spot. Carefully lift the distributor back out not moving the rotor. Lay the distributor straight back and look at the position of the slot. Turn the oil pump shaft to match the distributor. Back the rotor back enough so so that it rotates to the correct spot when all the way down. Usually takes me a couple tries to get It right.
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Old 06-12-2019, 07:34 PM   #4
71CHEVYSHORTBED402
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Re: What am I missing about ignition timing?

Quote:
Originally Posted by garyd1961 View Post
Set your distributor in the hole but don't engage the gears. Turn the rotor to the correct spot. Carefully lift the distributor back out not moving the rotor. Lay the distributor straight back and look at the position of the slot. Turn the oil pump shaft to match the distributor. Back the rotor back enough so so that it rotates to the correct spot when all the way down. Usually takes me a couple tries to get It right.
I think I see what you mean, and I did most of that. I believe you're saying turn the rotor to counter-clockwise a spot, so when it engages it lands toward the #1 cylinder. I'll give it a go.

Gave it a shot, I think it's right now (image). I started it with the rotor facing #1, spun the rotor counter clockwise some, dropped the rest and she appears correct now. On a side, I'm hiring out the first start on this, so they have to pull the distributor and prime anyway. But I like to know how things work.

OT: Both my 402 have HEI. The bolt that secures the brake booster bracket to the intake was removed from both trucks, because the bolt head doesn't clear one of the distributor cap hooks. 5/16-18 button heads are the ticket, you can buy them in black oxide.

Quote:
Originally Posted by truck-kid View Post
Sounds like you are engaged 1 tooth off as Rotor must point to #1 when fully engaged.Remove distributor and turn oil pump driveshaft counter clockwise slightly untill you can drop distributor in and it points towards #1 on the cap. You can verify correct position when your done by with #1 plug out turn engine over by having someone bump starter or turn over by hand untill #1 just starts to build compression then continue turning by hand till tdc marks align on balancer and timing tab.The rotor should point to #1 on the cap.
Thanks for the info.
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Tony


71 C10 Custom Deluxe, SWB, fleet, 402/400TH, A/C...Resource intensive......And (*^(*^ leaf springs. Speak of, looking for OEM rear sport bumper brackets for this ride. They're unlike those more common, even the outer brackets are different.

72 Cheyenne Super, LWB, fleet, C20, 402/400TH, A/C. Driver and tinker truck

Last edited by 71CHEVYSHORTBED402; 06-12-2019 at 08:28 PM.
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Old 06-12-2019, 08:24 PM   #5
garyd1961
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Re: What am I missing about ignition timing?

Quote:
Originally Posted by 71CHEVYSHORTBED402 View Post
I think I see what you mean, and I did most of that. I believe you're saying turn the rotor to counter-clockwise a spot, so when it engages it lands toward the #1 cylinder. I'll give it a go.
Yep, that is what I'm saying.
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