Cant hold timing - possible problems?

[PHOENIX]

1983 C10 w/ 350
Still has damper from 305 (at least 16 years old)
Dist. is Proform (just under 5-years old) w/ msd module and msd coil, everything else is as the proform comes.
Plugs and plug wires are not very old.

I has discussed this before. Well I havent played with it much, but the timing wont hold, its keeps changing on its own.

The dist. clamp is solid and has not let up and I cant turn the distr. by hand without loosening the bolt, so I know the distr. is not slipping and turning.

Ill set the timing and idle, after full engine warm up and with vacuum advance disconnected. Then I drive it around for a little while and then I check the timing again and its changed from 8 BTC to 12 BTC. If I dont mess with it, it continues to get worse. We have discussed the fact the the damper may be slipping. Because in the past the timing was way off yet the truck didnt run as bad as it should for timing that far off. I got under the truck and tried to turn the damper outside by hand and it did not budge, it was solid.

I did however notice that when I rev it kind of fast, quick short burst, there is a slight tick sound that comes from the distr cap area. It is just one little tick, it is NOT continious. I was able to track this sound down with my stethescope so I am pretty sure thats where the sound is coming from. I could not hear the sound on any other parts except the distr. cap and the metal base the cap sits on. I could not hear the tick when listening to the distr. shaft (leading into engine). Is it possible something is wore out inside the distr. and causing this problem?

When you rev up an engine the timing mark is supposed to return to the proper setting right away, right?

Well mine is slow and doesnt go back to where it was before you reved it up. I have a little video here that shows what I am talking about. It is sometimes more drastic then in this video. The timing in this video is at 12 btc, last time i adjusted it I set it at 8 and it changed itself to 12 in just 15 miles of driving. I didnt bother to adjust it back to 8 before this video. Note how slow the timing mark returns after I let off the throttle. When I set the timing at 8 and rev it like in this video it slows down around 12 and slowly returns to about 10 or so but doesnt seem to go back to 8. If I have time tomorrow Ill set the timing back to 8 and shoot a video of it this way too. Also the timing light is working properly, but for some reason the camera didnt like the flashing light and would stop the light flashing on the camera, not sure what the deal was so dont pay attention to the inconsistant light flashing, just watch the timing mark and listen to the engine.

BAD TIMING VIDEO 3.7MB-14 sec.

What the hell is going on here?
Its driving me crazy. What do I change the distr. or the damper. When I open up the distr. what do I look for as far as wear? Any and all help is appreciated.

Thanks, Eddie

[AirMale]

Pull the dist. and check the gear to make sure it's ok.
Then I would consider looking into the timing chain stretching or cam issues.....good luck!

[MSL]

you have a bad timing chain.

[Blue Beard]

Have to agree with MSL, more likely timing chain.

Just finished one on a friends truck.

[bigd65]

Let me throw an idea in there. What springs do you have on your advance weights inside the distributor. If they are to light for the idle you have your truck idling at, it will cause this same problem. eather lower the idle down or go a step or 2 heavier on the adavnce springs ( the heavier springs help with torque anyways)

[78chevstepside]

possible problem could be a bad or loose gear in your distributor. This will also make your timing change constantly. I have had this happen. what happen to me was the gear in the distributor would move up out of postion move a few teeth and then go back into postion. Causing my timing to change constantly. More then likely the timing chain is bad.

[swervin ervin]

Could be a bad timing chain I guess, but if the chain is bad, when checking the timing, the mark will bounce around with you. First thing I would do is find a known good distributor to try and see what happens then. If it does it then, more than likely you have some chain/gear problems.

When it does this, how does the truck run?

[PHOENIX]

The truck seems to run alright when the timing is set down to 8, there is not a miss or anything. There is sometimes a flat sport when changing from 1-2 then from 2-3 but it doesnt happen often and I do not know if its related. What I know is related though is the truck is running rough. Anything above 3000 rpm its not running smooth at all. When I change the timing back down to 8 it runs smoothly but it doesnt seem like it has the power it had before. Like I said the timing doesnt stay at 8 for too long so it starts running rough again.

I do not have another good distr. I could through in there to test it. So thats not likely.

The timing mark when at idle will slowly go down to a point then stop, it is not very clear on this video, but it will drop like in this video then slowly keep going down another 2,3 or 4 degrees. But it doesnt jump back and forth it only falls down (and not at a consistant speed).

Bigd65: Ill try to change the springs before I get into anything major.

When looking at the timing chain how will I determine it is bad?

When looking at the distr. gear how will I know if its bad, is the teeth damage obvious?

Thanks guys for the help, truck has been down for awhile and I need to get this stuff fixed. I have been borrowing my fathers car, but I dont know how long this can last.
Couldnt ride the bus to work if I wanted to because none go that route, I need my truck.

[PHOENIX]

Sorry ..... repost

[MylilBowTie]

Take the distributor cap off. Looking at the rotor button, move the bottom crank pulley back and fourth. This will tell you somewhat on the slack of the timing chain with out tearing the front half of the engine down.

[kwmech]

Grab the rotor after the cap is off and check to see if the mechanical advance is not sticking. If you twist the rotor and release it should twist back immediatley.