Worn out timing chain symtoms in a 307 Olds?

[kustomkyle]

I've read over and over again that Olds 307 timing chains wear out when they get close to 100,000 miles. That seems reasonable, I guess. I was wondering what the symptoms of such a situation would be.

I had some hard, dark chunks in my oil last oil change. I thought it was carbon, but I was told otherwise. So I'm assuming it was plastic, since they did not stick to a magnet. The engine also has a lot of loud spark knock or detonation, usually the worst at shift points (2nd to 3rd in a 200-R4). Getting the timing tuned in with a timing light helped a lot, but it seems to be going back to the way it was gradually.

Also, if the chain is worn out, what danger does it pose to the engine? Will it snap or something? If the plastic parts are worn, what significance does that have?

EDIT: I forgot to mention that the engine turns over very slow on random days. It did it for about a week in the summer when it was about 100 degrees. It went away, and now that it is getting cold out, it is doing it again every once in a while. I had the battery tested, and it was read as having full voltage. If it was the starter, wouldn't it just get worse until it wouldn't start at all? Cleaning the negative battery ground on the engine seemed to help in the summer, but it appears to have corroded again for some reason. I don't know if this is related or not.

 

[joe_padavano]

I've read over and over again that Olds 307 timing chains wear out when they get close to 100,000 miles. That seems reasonable, I guess. I was wondering what the symptoms of such a situation would be.

I had some hard, dark chunks in my oil last oil change. I thought it was carbon, but I was told otherwise. So I'm assuming it was plastic, since they did not stick to a magnet. The engine also has a lot of loud spark knock or detonation, usually the worst at shift points (2nd to 3rd in a 200-R4). Getting the timing tuned in with a timing light helped a lot, but it seems to be going back to the way it was gradually.

Also, if the chain is worn out, what danger does it pose to the engine? Will it snap or something? If the plastic parts are worn, what significance does that have?

I usually replace my timing chains between 80,000 and 100,000 miles as a preventative maintenance item. Many cars (most Olds motors among them) used plastic teeth on the cam gear to reduce noise. The plastic wears down and at some point the chain just comes off. At a minimum, the engine stops running. If the engine is an interference design, valves can contact pistons. Bent parts ensue.

You can get an idea of the wear in the chain and gears by pulling the distributor cap and watching the rotor while rocking the crank back and forth with a breaker bar. This is a very UNscientific test, however. A better thing to do is to just replace the timing set after 80,000 miles or so.

 

[dan2286]

What kind of oil are you using? If the oil is to thick it can cause slow cranking in the winter. Also, if their is a lot of carbon build up in the combustion chambers it can cause detonation. Have you tried using any Seafoam or GM top end cleaner?

As Joe said, it is just a really good idea to change the timing chain at around 100,000 miles just to be safe. It can cost you a lot more money i it decides to break and you have an interference engine.

 

[bigdan]

100,00 miles ;change the kit before it breaks....

put a true roller timing set ..it is worth it! much less prone to failure and will last longer then the original design
dan