390 Timing ?'s
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390 Timing ?'s
I have a 72 F250 w/ a 390. I have owned the truck a few months and I'm working though the process of making sure the motor is running right. Before I replaced the points w/ a Pertronix electronic ignition and a new Pertronix flame thrower coil I checked the timing and it was at 2 degrees BTDC. The truck started up just fine and idled great.
After I put in the electronic ignition, I checked the timing and it was at 12 degrees after TDC. The factory setting should be about 6 degrees before TDC. I reset it to 6 BTDC and adjusted the idle and it is quite a bit more responsive when I drive it. Why would it have been off so much? Would the installation on the electronic ignition module have changed the timing?
Thanks for the help.
After I put in the electronic ignition, I checked the timing and it was at 12 degrees after TDC. The factory setting should be about 6 degrees before TDC. I reset it to 6 BTDC and adjusted the idle and it is quite a bit more responsive when I drive it. Why would it have been off so much? Would the installation on the electronic ignition module have changed the timing?
Thanks for the help.
Post Fiend
Joined: Mar 2004
Posts: 6,056
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From: Union, Washington
The electronic pickup is not in the same place the points were. I have never installed an electronic conversion without this happening. I did hundreds of them when I was a recreational marine mechanic.
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I took the truck out for a drive today and it seem to run well. However, as I was climbing a hill on the interstate I could hear a new noise that I had not heard before. It wasn't really loud but it was there. I believe it was a knocking or pinging sound. My timing is at 6 BTDC. Should I move it and if so which way should I move it? Thanks.
Post Fiend
Joined: Mar 2004
Posts: 6,056
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From: Union, Washington
Initial timing really means nothing unless you know what you total mechanical advance is. Total mechanical advance should be at least 34° but no more than 38°. Then you need to know how much advance the vacuum system is stacking on top of the total mechanical advance.
Laughing Gas
Joined: Aug 2008
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It might be wise to check that the timing marks on the damper are correct. The outer damper ring can slip and cause the marks to be incorrect. Using a piston stop tool, gently rotate the engine gently both ways until it stops and mark the damper in the two spots. The TDC mark should be exactly between the two marks.
Removing the sparkplugs makes gentle rotation of the engine easier....use a long socket wrench on the damper bolt and rotate CW when viewed from the front.
A slipping damper can cause you to have the timing set far more advanced than it appears and that can cause detonation. It happened to me and I broke a piston.
This might explain why your measured timing before the conversion was ATDC.
On your initial question, I agree with Bear.....when installing a pertronix, the timing will change and have to be adjusted. Simply changing points will also cause timing changes unless the exact same gap is used. And even then, inconsitencies in the manufacturing of the points may still cause a timing change.
Removing the sparkplugs makes gentle rotation of the engine easier....use a long socket wrench on the damper bolt and rotate CW when viewed from the front.
A slipping damper can cause you to have the timing set far more advanced than it appears and that can cause detonation. It happened to me and I broke a piston.
This might explain why your measured timing before the conversion was ATDC.
On your initial question, I agree with Bear.....when installing a pertronix, the timing will change and have to be adjusted. Simply changing points will also cause timing changes unless the exact same gap is used. And even then, inconsitencies in the manufacturing of the points may still cause a timing change.
Freshman User
Joined: Aug 2009
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Since this is a timing thread this is only a partial hijack. Ive always set the timing at whatever is called for at idle. My son recently got an engine for his 68 VW Baja from an online builder. In the break in instructions it said to set timing, rev the engine till the timing doesnt advance further, set to 28-32 degrees. This method made the timing at idle a good bit off, though it ran fine. I wanted to follow the builders instructions to a T just in case..... Have any of you timed an engine like this? Can or should we do it on these FEs?
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Laughing Gas
Joined: Aug 2008
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The max timing is the most important. Timing can often hit max below 3000 rpm, and it's this range and higher where most power is made and timing is most important.
You can set the timing for the correct max and take whatever the idle timing gives you, but you don't have to. You can adjust the internal distributor mechansim to achieve the inital timing, amount of mech adavnce, and the rate of advancement you want.
I'd follow the recommendations and set for max timing. If the engine knocks a bit down low, or seems sluggish down low, then you can adjust the distributor internals.
You can set the timing for the correct max and take whatever the idle timing gives you, but you don't have to. You can adjust the internal distributor mechansim to achieve the inital timing, amount of mech adavnce, and the rate of advancement you want.
I'd follow the recommendations and set for max timing. If the engine knocks a bit down low, or seems sluggish down low, then you can adjust the distributor internals.
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Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Since this is a timing thread this is only a partial hijack. Ive always set the timing at whatever is called for at idle. My son recently got an engine for his 68 VW Baja from an online builder. In the break in instructions it said to set timing, rev the engine till the timing doesnt advance further, set to 28-32 degrees. This method made the timing at idle a good bit off, though it ran fine. I wanted to follow the builders instructions to a T just in case..... Have any of you timed an engine like this? Can or should we do it on these FEs?
Freshman User
Joined: Aug 2009
Posts: 31
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Nevermind, just did a search and you already answered here, thanks dude.
https://www.ford-trucks.com/forums/9...c-advance.html
https://www.ford-trucks.com/forums/9...c-advance.html
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