What causing timing to change?

[PHOENIX]

Info on my setup.
Stock 350 engine (I guess the miles at being around 60,000)
Proform (In know), distributor
with msd module and coil (thanks to a member here )
AC Delco plugs (about 6-months old)
Taylor plug wires, in great shape still

Anyway I recently had some problems with strange noise from my truck. I checked the timing and it was way off. What causing timing to change like this? I had it set at 10 and it was probably around 24 or so. Truck seemed to run fine at the 24, but when I returned it down to 8-10 it ran much smoother and a little stronger. What the heck causes the timing to change like that?
Also when I was changing the timing back down it would slowly go down 10...............9...................8. In about 15 seconds or so I could see it dropping down. I tried it a few more times and got it to stay around 8. Everything seems fine now, but I need to check on it later today or tomorrow. Once again, what the heck causes timing to change on its own? YES my distr. hold down tab was tight, I could not move it by hand until I loosened the bolt.

Thanks for your help!

[bpmcgee]

Could the outer ring on your harmonic damper be slipping?

Brian

[AirMale]

Check the dist. gear for wear and if that is good you may have cam play.

[79BIG10]

When you checked the timing you made sure to pull the vacuum port off the HEI right? If so then it could have been the outer ring like mentioned or a bad timing chain.

[swervin ervin]

The only time I've ever seen timing do this was when the balancer key way was missing letting the balancer spin on the crank. Strangest thing I've ever seen. I have no idea where the key went but it was gone. Nothing broken or ripped out, just gone from the crank. Only thing I could figure is when the balancer was installed it must of pushed on the key and it finally worked it's way out.

[PHOENIX]

Strange is right. Damn thing was driving me crazy. Plus I bumped my head on the hood latch (does someone make a protective pad to put on them?).

I did have the vacuum line off the distr.

I will inspect the balancer further to see what I can find.
If the balancer is slipping, how can I tell?
Will I be able to turn it by hand (with the engine off)?
I would hate to pull the dist. to check for wear, but If I dont see anything wrong with the balancer I may inspect that.

Thanks for everything guys, keep the ideas coming if you have any.

[swervin ervin]

Only true way I know of to check the balancer is with a piston stop.

As for the bumping head deal. I hit mine on one of our damn computer desks a few minutes ago. Don't ask. This is what really gripes me about being bald. When you hit your head, it brings the blood.

[ocbaud]

i've come SO close to hitting my head on the latch. i've missed everytime, and thats a good thing, because if i would have hit it as hard as i hit the spot right next to it, i would probably be sitting here drooling with my arm to my chest

[dswancutt]

Check your timing gear and chain. If it is original GM, then it has the nylon teeth. My 78 has an early 80's 305 and the timing gear went out. I pulled up to a stop and it just died and wouldn't start. I had never checked the timing before this happened but it was running like crap. Just before it died, I heard a strange grinding noise that was the timing change rubbing on the cover. I was lucky that it did not give out at speed as it would have screwed up the motor.

I don't know if this is the problem but it is fairly easy to check & replace.

Doug

[PHOENIX]

I have been meaning to buy a piston stop for a long time now.
Ill see if my dad has one. When you use them you just take out the #1 spark plug and screw in the piston stop, set the depth on the piston stop and turn the engine over by hand (with tool on crank). The piston will bump the piston stop and it will not want to turn anymore? Ihavent used one and I would hate to break something.

Doug,
My crate motor is about 5 years old or so (maybe 6), were they still using the nylon teeth? I was thinking it may be something to do with the timing chain too.
Ill try the TDC first, because thats easy. I guess I go from there.

If this helps at all. When we installed the crate motor we used the balancer off the 305 and just changed the timing mark (compared to a new 350 balancer at the dealer). So the balancer is rather old (maybe original).

[swervin ervin]

Since it's the old 305 small balancer, it would be suspect for slipping.

On the stop. You got it. Rotate the engine until it makes contact with the stop. Do it slowly so you don't damage the piston. Make a mark on the balancer where it lines up with the 0 on the pointer. Then rotate the other way and do the same. TDC will be center ways between the two marks. If the balancer is OK, should be on original mark you made, or on the stock mark if it has one.

[PHOENIX]

Ok Mike now you confused me just a little bit.
Stick the stop in, rotate the engine clockwise until it hits the stop.
Make a mark on the balancer at 0
Then rotate counterclockwise until it stops (hits the stop) again?
Make another mark on the balancer at 0
The TDC will be midway between the two marks I made on the balancer?
Do I just put a measuring tape on it and mark the middle point between the two marks I made?
Because the balancer is round how do I know which midway is right?
Maybe I got this all wrong

[CRRoy71]

That is right.

I did this recently, and I just used a measuring tape like you would use on fabric. You know one of those like a ribbon. Worked like a charm.

[flip66]

had the same problem it was the balncer. I was tinking with it and adjusting stuff had it running good so I went to check the timing one more time just to make sure and it was way off I could not understand why it ran so good but the time was off so bad all the sudden. Went to reset it and the thing would die not run or not start got to looking at and noticed the rubber peice between the two peices on the balancer was hanging out just a litle.

[Kenneth]

As for the latch, if I'm spending more than a couple hours under the hood, I just remove the latch from the hood. It takes about 30 sec. That thing hurt the first time I hit it and that was enough from me.