keeps jumping timing???

[dman1982]

i got a 84 k10 4x4, my timing keeps jumping around on me, weve adjusted once about a month or so ago and ran fine, it jumped timing again and is starting to flood out, had to leave it at work a couple days....but got her home and wanted some advice before i start ripping her apart.

[3r!c84]

is the dizy hold down tight?

[dman1982]

oh ya...thats was the first thing i checked

[BigBlocksRule]

Loose/worn timing chain would be the next place I'd check.

[dman1982]

ya thats what im thinking....they dont cost a whole lot either....any other suggestions? thats kindof a PITA job.

[dman1982]

does anyone else have any other suggestion before i start tearing this thing apart?

[gchemist]

One, the harmonic balancer is shot. Two, the nylon gears on chain are starting to fail. Is vacuum constant on the HEI?

[dman1982]

on not sure on the vacum but ill check that out tommorow....last time i checked it was all good

[dman1982]

gchemist.....are you telling me about the harmonic balancer or telling me? lol how do i check it?

[gchemist]

Originally Posted by dman1982

gchemist.....are you telling me about the harmonic balancer or telling me? lol how do i check it?

Your problem can be both. Grab the outside ring. Can you move it? Put a strap wrench on it. With that many miles, the nylon gears will break off at any time. A timing chain failure finished off the original 305 in my truck.

This happens when nylon coated gears fail!

[nbpro]

spark control module
distributor removal required to remove pick up coil. magnets shouldnt be cracked. while distributor is out check for knifedging on the drive gear.

[DaSchlange]

Originally Posted by nbpro

spark control module

That's what I was thinking at first, but the module doesn't actually cause it do jump does it? I thought if the module went bad it just didn't fire at all.

[nbpro]

Originally Posted by DaSchlange

That's what I was thinking at first, but the module doesn't actually cause it do jump does it? I thought if the module went bad it just didn't fire at all.

not saying it's his problem just some thing to check
The Electronic Spark Control, also called the Knock Sensor, is an electronic device built by General Motors to help regulate the timing inside of the engine.
http://www.73-87.com/7387garage/drivetrain/escrepl.htm
post by gchemist
http://www.chevytalk.org/fusionbb/sh...hp?tid/176666/

http://67-72chevytrucks.com/vboard/s...d.php?t=416801
The ESC distributor used a 5 pin ignition module. The ESC distributor had two plugs coming out of the distributor, one plug going to the cap / coil assembly, and the other plug went to the spark timing controller

[LONGHAIR]

The real problem with "jumping timing" on the ignition by a timing chain slip is that the cam timing is now late too. This is going to cause problems that are bigger than ignition.

The next issue is that it's not a simple "replace the gears and chain" type of thing. Those nylon teeth off of the cam sprocket had to go somewhere...... The oil pan and oil pump will be full of that junk.

[dman1982]

im not sure if i have a spark control module....isnt that for fuel injection???

[dman1982]

i forgot to mention that this engine has about 200-300k on it...i do plan on dropping another engine into it...but thats going to be closer to spring

[dman1982]

well im going to be jumping into this project tommorow. dont have time today or i would be

[Cue-Ball]

Is the timing moving around if the vacuum advance is unplugged? If not, you could have a defective vacuum advance or a torn diaphragm. I'd also check the centrifugal weights in the distributor. They could be sticking, which would explain the timing being different from week to week (even if the vacuum advance is unplugged and determined not to be the problem). Definitely check those two things before you start ripping into the engine to check harmonic balancer and timing chain.

[dman1982]

hey cue ball...ill definetly check that before i start getting into all that stuff

[BigBlocksRule]

^ you betcha, good advice.
There's not many things that are worse than doing a big tear-down or re-work and finding out the problem was much simpler and easier to fix!

[dman1982]

bigblocksrule......i know exactly what you mean....ive encountered that way too many times...really freakin sucks...lol...but atleast you got new and extra parts sometimes lol