Timing fluctuating

[grubsster]

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

[YoungPup1977]

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 !!!!

[68gmsee]

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.

[mattfranklin]

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?

[grubsster]

Originally Posted by mattfranklin

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?

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...

[mattfranklin]

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.

[Tiger Joe]

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?

[grubsster]

Originally Posted by mattfranklin

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.

Thanks for the replies. Everything is new except the carb and distributor. I transferred those from my 327. No grime and aluminum intake. I ran temporary grounds which are in the picture... harmonic balancer is good, also bolted in place. The rpm also changes as the fluctuation occurs. I visually did see the arcing at the base of the distributor. I'm sure its an electrical issue. I'm going to try plug wires and then cap. Still looking for a short though...

[YoungPup1977]

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...

[grubsster]

Originally Posted by YoungPup1977

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...

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...

[D13]

Worn distributor shaft bushings or drive gear will cause fluctuating timing.

[68gmsee]

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.

[grubsster]

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...

[YoungPup1977]

Originally Posted by grubsster

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...

The best thing is, something changed it. The stall of the TC should be about 500 RPM more than the start of the curve of the camshaft. Check your cam specs off the cam card for the cam you installed in your new engine. For example, it may indicate 1800 to 5200. So I would start at 2300 stall speed for the TC. Just for starters. Good luck !!!!
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[toolboxchev]

Originally Posted by D13

Worn distributor shaft bushings or drive gear will cause fluctuating timing.

X2 Go with it!