Timing changes on its own

[motormischiefandfire]

My 1995 gmc sierra hasnt been running right since i put a new distributor in, no matter how much i tighten it or anything the timing seems to change after the first trip. The truck likes to stall at red lights and stop signs and doesnt like to start without starting fluid. Do you think my distributor is bad? What do you suggest i do. I do disconect the timing advance wire from under the dash as well. Ive also put a washer on the distributor retainer bolt.

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[JWOK]

How many times did the timing change? If you dropped in the dist. without properly engaging the oil pump drive, it could end up dropping, becoming loose and turning after the engine was run. Was the dist. loose after the timing changed?

 

[motormischiefandfire]

It didnt feel loose, and ive had oil pressure. How loose would it have been? Sometimes it was loose enough to turn just a little but always pretty snug yet. Usualy it would change by about 4 to 8 degrees

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[JWOK]

If you have adjusted the timing multiple times and the distributor was still snug when it happened then that is probably not because of oil pump drive engagement. That would hold the distributor off the intake enough that it would be very loose after engaging. Why did you replace the distributor in the first place? If the timing keeps changing by 4-8 degrees and the distributor body is not turning, something else is moving. Most likely culprit may be timing chain jumping teeth which would also explain hard starting. It is also possible to have the pickup assembly in the distributor loose. Look inside the distributor to make sure everything is correct, then I would lean toward a timing chain issue if you are certain the distributor body is not turning.

 

[motormischiefandfire]

I had been kind of suspecting timing chain issues , but shouldnt that cause my valves to be out of time with the piston? Ill check the distributor when i get home from work here

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[JWOK]

Valve timing will be off, but a stock tbi 4.3/5.0/5.7 engine will not have a problem with valves hitting pistons with the cam being off a few degrees. The engine can run this way up to a point, but you will definitely notice issues.

 

[motormischiefandfire]

Thats very good to know, thank you

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[thinger2]

There are known problems with after market distributor ends being machined wrong.
But, the one thing I have seen over and over is that the aftermarket gasket is paper thin.
Its not just a gasket, its a "friction gasket"
In other words it helps to keep the dist from spinning.
If it is to thin, the drive end burries too deep into the oil pump shaft and binds up which will twist and bend the housing as it climbs out of the helical gear.
Try getting a GM seal for it. They are at least 2 times thicker and not just cardboard.
Its a big deal because the collar on the pump drive is plastic and can come apart.
That seal also helps control lash on the distributor gear and if its wrong it might chip the teeth off

 

[thinger2]

You can also get an idea about timing chain slop by pulling the dist cap off and pull all of the plugs. Put a breaker bar on the crank bolt and turn the crank while you look at the rotor to see how far you need to turn the crank before the rotor turns.
You can also disconnect the timing wire and paint the timing marks.
They need to be clean and well marked
Put a timing light on it and see if it "hunts" around for TDC as you blip the throttle a few times.
this takes some pretty close observation and a bit of practice but, if its bad, you will see it move before and after TDC

 

[motormischiefandfire]

Ill definitely have to check for slop with the timing mark, ive already got it marked because it makes it a lot easier to time. I just put a distributor in from my parts truck tonight because ive been dailying the truck since my blazer went to scrap and i gotta get around some how. It runs a hole lot better and im pretty sure the pickup coil in the accel one i had was junk. I do plan on eventually replacing this one with an msd, the rotor has some play going up and down and doesnt spin completely freely. Works for now untill i can buy the one i want. I have made the decision not to buy accel products any more. I havent had any luck.

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