03-13-2018, 05:35 PM | #1 |
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Timing fluctuating
Hi all,
I installed my rebuilt 283 over the weekend and have a strange issue. When I try to set initial timing my mark fluctuates about 15 to 20 degrees. Every once in a while it stabilizes then fluctuates again making everything else such as idle fluctuate. Also while trying to move the distributor which is an MSD street fire HEI I noticed arcing at the base where the hold down is located. So I'm sure this arcing had to do with my fluctuation but what could be causing the arcing? I tried grounding to the distributor housing but that had no effect. Thanks in advance |
03-13-2018, 11:45 PM | #2 |
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Re: Timing fluctuating
I always put some dielectric silicone on top of the Dizzy shaft when replacing the rotor which prevents spark from grounding out thru the rotor.....Good Luck !!!!
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03-14-2018, 09:46 AM | #3 |
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Re: Timing fluctuating
I've had defective distributor caps arc before. They may have hairline cracks where moisture gets in or accumulates and causes the arcing. In some cases you can see where the cracks are but not always. I'd start with replacing the cap first.
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03-14-2018, 03:35 PM | #4 |
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Re: Timing fluctuating
Just so we can get a clear visual -- when you say "hold-down," do you mean the hold-down clamp that screws into the manifold?
https://www.summitracing.com/parts/msd-8110 Or the quarter turn screws that hold the cap to the housing?
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03-14-2018, 03:52 PM | #5 | |
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Re: Timing fluctuating
Quote:
The hold down to the manifold... trying to figure out why the distributor would arc at all. Also the mark when timing will jump 15 to 20 degree plus or minus. I'm going to check the cap and rotor along with verify I have the firing order right... |
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03-14-2018, 04:06 PM | #6 |
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Re: Timing fluctuating
That arcing is a mystery. I'm trying to think about it. I have had engines before that were not grounded to the frame and had problems, but it's a different problem. One where the only ground is the fuel line and it gets hot and percolates the fuel.
Are you actually seeing the arc or a reflection of the arc on the shiny parts? Could it be that a bad cap or wires are arcing and you're seeing the other parts light up rather than seeing the actual zap? Now I'm grabbing at straws... Could it be that you have a varnish or carbon deposit that is is so strong it insulates the distributor body from the manifold? Could it be two different problems? When I hear that timing is fluctuating my immediate gut response is mostly timing chain (or distributor gear?). But if those parts are new we can probably rule that out. Keep us posted.
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(Very) Slow-Going Build Thread: Stock 1970 Short Step with Stock 1970 LT-1 http://67-72chevytrucks.com/vboard/s...d.php?t=567340 |
03-14-2018, 04:35 PM | #7 |
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Re: Timing fluctuating
for the arching:
is your intake manifold painted? IIRC, the distributor is grounded to the intake manifold there, so if you have paint/dirt/grime you may not be getting a good ground. for the timing: 1- is the chain new? I assume it is but you never know. 2- is the harmonic balancer tight? it could be wobbling? |
03-14-2018, 07:12 PM | #8 | |
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Re: Timing fluctuating
Quote:
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03-14-2018, 09:34 PM | #9 |
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Re: Timing fluctuating
Do you have another dizzy to try....I am only a few miles away, I have an extra one...that is a known good one...
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03-14-2018, 09:45 PM | #10 |
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Re: Timing fluctuating
Thanks, I may take you up on your offer. I'm going to verify that I didn't mix the wires up along with the fact they are cheap off the shelf advance auto wires used for break in purposes so they may be the problem as well. I'll pull the cap and look for anything obvious there then it's probably time to start chucking parts at it...
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03-15-2018, 06:13 AM | #11 |
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Re: Timing fluctuating
Worn distributor shaft bushings or drive gear will cause fluctuating timing.
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03-15-2018, 10:18 AM | #12 |
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Re: Timing fluctuating
Sometimes a good way to check for and locating arcing in spark plug wires and/or distributor is at nights by spraying the parts lightly with a fine mist of water. If not sure where it's coming from the best and quickest way is swapping dizzy like youngpup menitioned.
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68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
03-17-2018, 07:32 PM | #13 |
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Re: Timing fluctuating
Hey all,
Update... So while troubleshooting the fluctuating timing I came across a few things. The first of which was my vintage snap on dial back timing light was not working properly. I used another light I had in the toolbox and got that straightened out. The second issue was that I am using an MSD streetfire distributor. Apparently it goes into mechanical advance a little early. I think the idle was right on the edge of going in to advance so that was creating the "fluctuation" I did change the cap to a new one and put the dielectric grease on the rotor button. With all of that it sits right where i wanted with no arcing or fluctuation. Now to figure out what stall torque converter... Thanks to all who helped... |
03-18-2018, 02:55 PM | #14 | |
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03-31-2018, 02:34 AM | #15 |
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Re: Timing fluctuating
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