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Timing light advance measurement doesn't stop
#1
Wrench 
Today I was testing my newly installed 408 stroker. I am using the OEM distributor that I had recently disassembled and cleaned. The distributor has the 10L slot that should be good for 20 degrees advance. The initial timing is at 12. The weird situation is that as I go up in RPM the advancing seems to never stop. It went all the way to 50 before I lower the RPMs. I don't know if it will stop at 50 but I just didn't want to go any higher. Upon return to idle the timing was back at 12. Tested several time with the same outcome. I have the feeling that something may be wrong with the timing light because it doesn't seem to make sense. I think the engine won't be able to run with a real 50 advance. When I had it running with "50" advance it sounded and run fine. Does anyone have an idea of what am I doing wrong? Could it be a setting of the timing light?

Edit: I did have the vacuum disconnected.

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
4-wheel disc brakes
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#2
I would take the cap off and turn the rotor by hand, see if it stops where it should, to rule out a problem with the advance mechanism. If that is OK, then it has to be the timing light. Do you have another timing light that doesn't have the advance feature?



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#3
(10-04-2018, 03:22 PM)Don C Wrote: I would take the cap off and turn the rotor by hand, see if it stops where it should, to rule out a problem with the advance mechanism. If that is OK, then it has to be the timing light. Do you have another timing light that doesn't have the advance feature?

I rotated it and stops after a small rotation. I tested that before putting the cap in. I will have to recheck. Once I go back home I will dig the instructions of the timing light to see if there is some weird feature that is on.

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
4-wheel disc brakes
  Reply
#4
A thought. I have a Street Fire (by MSD) CD ignition box. Could the multiple spark of the CD ignition fool the timing light somehow?

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
4-wheel disc brakes
  Reply
#5
Is the OEM vacuum advance connected? If so it can add 15+ degrees of additional advance. Chuck
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#6
(10-04-2018, 05:50 PM)c9zx Wrote: Is the OEM vacuum advance connected? If so it can add 15+ degrees of additional advance. Chuck

The vacuum canister is on, but with the hose disconnected.

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
4-wheel disc brakes
  Reply
#7
If it is a dial back timing light, set it on zero. They have been known to give false readings due to the potentiometer being less than perfect. Chuck
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#8
Checked the distributor and all looks good. I can rotate the rotor slightly until it stops and then springs back. I didn't measure but it is a very small movement. The breaker plate is attached to the vacuum advance arm and it is very tight.
I will check timing again this weekend making sure that the pickup clip is separated from the other wires and revving it past 3,000 RPM, which from what I understand is the RPMs at which the CD stops.

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
4-wheel disc brakes
  Reply
#9
When I did mine and I'm sure you've read my saga on timing issues, I had a similar thing happening. That's when I started playing with the springs and tension. For sure I think it could be your timing light, so try another if you can.
What springs are you using? You have a good base imo, with the 10L slot, but to control the rate of advance needs spring tweaking. On MY engine, I found the factory heavy spring, set on the pegs with only slight free-paly and a Mr. Gasket 925D spring on the other pegs, worked best for me. Also, my vacuum advance canister is adjustable and I turned it back to give only 4-6 degrees of vac advance. Also, don't forget to plug your vac line when you disconnect it, made that mistake before!
My numbers are; 10L slot, 20 deg. crank, 16 deg. initial, 4-6 deg. vac adv. and springs as mentioned. My result is a strong pulling motor, no rattle.
Now, I realize your motor at 408 may change things beyond anything I know (which ain't much!!), so hopefully you'll get it figured out. Be sure to let me/us know.
Good luck,
Geoff.
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#10
(10-05-2018, 09:40 AM)Stanglover Wrote: When I did mine and I'm sure you've read my saga on timing issues, I had a similar thing happening. That's when I started playing with the springs and tension. For sure I think it could be your timing light, so try another if you can.
What springs are you using? You have a good base imo, with the 10L slot, but to control the rate of advance needs spring tweaking. On MY engine, I found the factory heavy spring, set on the pegs with only slight free-paly and a Mr. Gasket 925D spring on the other pegs, worked best for me. Also, my vacuum advance canister is adjustable and I turned it back to give only 4-6 degrees of vac advance. Also, don't forget to plug your vac line when you disconnect it, made that mistake before!
My numbers are; 10L slot, 20 deg. crank, 16 deg. initial, 4-6 deg. vac adv. and springs as mentioned. My result is a strong pulling motor, no rattle.
Now, I realize your motor at 408 may change things beyond anything I know (which ain't much!!), so hopefully you'll get it figured out. Be sure to let me/us know.
Good luck,
Geoff.
I followed your advice as a starting point. I am using one from the Mr. Gasket set with the lightest of the two springs that were on the distributor (but it was heavier than the Mr. Gasket). Since I am reading up to 50 advance without vacuum connected I can only think that it is timing light issue. I don't have another a timing light. I may have to borrow one if the problem persists.

        [Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
4-wheel disc brakes
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