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#1 |
Senior Member
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Location: CA
Posts: 5,522
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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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#2 |
Registered User
Join Date: Feb 2004
Location: Massachusetts
Posts: 269
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Sounds gooey, it should snap back freely.
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72 Cheyenne Super 4x4 SWB |
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#3 |
Registered User
Join Date: Jun 2002
Location: central pa
Posts: 1,525
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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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72 longhorn c30 502BB/th400/fact air/4.11rear/ custom camper 72 bug(the better half's) under reconstruction 2009 HHR aqua blue 71 GMC k20 350/sm465 2009 Chevy hd3500 6.6 Victory Red crew cab dually Dave & Jeanne |
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#4 |
Registered User
Join Date: Jan 2000
Location: Wyoming USA
Posts: 2,445
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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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2001 Silverado K-1500 2005 FXDWG stage3 69 CHEVY Short/Step 327/4L60 373 posi 63 IMPALA 327 |
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#5 |
Registered User
Join Date: Jun 2003
Location: Linden, North Carolina
Posts: 617
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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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64 Panel Rebuild Pics Clutch Replacement and Borg Warner T10 Trans Rebuild 64 Panel 1/2 Ton 350cubes/400hp BorgWarner t-10 3:73 Auburn Posi |
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#6 |
Senior Member
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Location: CA
Posts: 5,522
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Thanks for the help. I'll go pull it apart and give it a thorough cleaning.
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#7 |
Senior Member
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Location: CA
Posts: 5,522
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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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#8 | |
Registered User
Join Date: Jun 2002
Location: Knoxville Tenn.
Posts: 3,058
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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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#9 |
Senior Member
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Location: CA
Posts: 5,522
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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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#10 |
Registered User
Join Date: Jun 2002
Location: Knoxville Tenn.
Posts: 3,058
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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 |
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#11 |
Senior Member
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Location: CA
Posts: 5,522
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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. |
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#12 | |
Registered User
Join Date: Jun 2002
Location: Knoxville Tenn.
Posts: 3,058
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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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#13 |
Registered User
Join Date: Feb 2002
Location: Vacaville, CA
Posts: 2,746
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Most SBC like 36°-38° total mechanical timing. Thats initial plus mechanical, vacuum disconnected.
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![]() ![]() 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI |
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#14 |
Senior Member
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Location: CA
Posts: 5,522
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Mine's way too low then. Can this be adjusted easily?
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#15 |
Registered User
Join Date: Feb 2002
Location: Vacaville, CA
Posts: 2,746
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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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![]() ![]() 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI |
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#16 | |
Senior Member
![]() ![]() Join Date: Jan 2005
Location: CA
Posts: 5,522
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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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