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07-16-2005, 01:50 AM | #1 |
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HEI Mechanical Advance Question
I replaced my HEI cap and rotor this afternoon and noticed that if I twist my rotor clockwise, it moves about 30 degrees, and the mechanical advance weights wind up and stick out. Then if I let go of the rotor, the rotor very, very slowly returns about half way back. The mechanical advance mechanism seems to be sticky. Is this normal, or should the rotor spring back into position quickly?
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07-16-2005, 02:07 AM | #2 |
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Sounds gooey, it should snap back freely.
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07-16-2005, 07:55 AM | #3 |
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It is probably rusty and week springs. Liquid wrench or PB blaster should loosen it up. The springs on the weights are what pulls it back. Later units had plastic bushings on the weight pivot arms. If they are still good then it is on the shaft lower down towards the pickup coil.
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07-16-2005, 02:52 PM | #4 |
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Yes it should snap back something is binding or wore out you can get an advance curve kit for under $10. and it will come with those plastic bushings.plus you can adjust the springs to your spec.
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07-16-2005, 03:21 PM | #5 |
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I usually find it's the shaft/bushings are gummed up. Take the dist apart and clean the shaft near the top. I had one out of a Vette that was soo gummed up I couldn't get the shaft out to clean.
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07-16-2005, 05:02 PM | #6 |
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Thanks for the help. I'll go pull it apart and give it a thorough cleaning.
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07-16-2005, 07:15 PM | #7 |
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After getting it cleaned up, it snaps back now. I have my timing set at 10 degrees. The mechanical advance gives me another 10 degrees of advance, and the vacuum gives another 10 degrees of advance for a total advance of around 30 degrees. Does this sound about right?
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07-16-2005, 11:52 PM | #8 | |
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Quote:
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56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer |
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07-17-2005, 12:41 AM | #9 |
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I'm not totally sure what the rpm was. I just rev'd the engine up (with the vacuum advance hose disconnected) until the timing stopped advancing. I'm guessing it was at around 2000-2500 RPM. Then I hooked up the vacuum advance hose and did the same thing. It reached a point where no matter how much faster I rev'd the engine, the timing didn't advance anymore. At what RPM should the mechanical advance top out?
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07-17-2005, 12:51 AM | #10 |
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Get me the # off the dist. base and I will look it up for you tomorrow and get back with you. It will be a # such as -11113452 or 11014364 or the like.
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56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer |
07-17-2005, 01:06 AM | #11 |
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That would be awesome. Where should I look for that number?
How would I go about figuring out how much total advance is optimum for my engine? I have a 300 HP 350ci. |
07-17-2005, 01:25 AM | #12 |
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Most SBC like 36°-38° total mechanical timing. Thats initial plus mechanical, vacuum disconnected.
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70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI |
07-17-2005, 01:32 AM | #13 |
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Mine's way too low then. Can this be adjusted easily?
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07-17-2005, 01:36 AM | #14 |
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Yes, check out these articles:
http://www.sporttruck.com/techarticl...03/index5.html http://www.73-87.com/7387garage/drivetrain/hei.htm
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70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI |
07-17-2005, 02:20 AM | #15 | |
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Thank you neonlarry for the articles. They were very helpful. This is the part I found most interesting:
Quote:
Last edited by pjmoreland; 07-17-2005 at 02:21 AM. |
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07-17-2005, 01:57 PM | #16 | |
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Quote:
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56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer |
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