Hi Everyone,

I managed to replace the timing chain on my 2.8 V6 this past weekend, and I found something very weird. More details below.

I had several symptoms that my Firebird was having valve timing trouble. It was hard to start, had even low compression across every cylinder, and had a rough idle, as if it had a large overlap cam. Judging by the lack of maintenance to other sections of the engine, such as the valve cover gaskets and fuel filter, I assumed that the timing chain was never changed. By the way, the car has 208,000 Miles on it, and was well past due to say the least.

After fighting every bolt for two days, I finally dug down to the timing chain. I set the engine to top dead center by the harmonic balancer, before I began. I noticed the timing chain had lots of slack between the timing chain and the timing tensioner. However, even with the slack, the dots on the timing gears lined up. I found this odd, but continued to remove the timing gears. I decided to line up the old crank sprocket with the new sprocket, and I discovered something that I have never seen before. The teeth on the old sprocket had "shifted" around the sprocket every little bit per tooth. It was enough that the top tooth on both sprockets, the one containing the alignment dimple, would line up, but the teeth started "moving" as they went around the old sprocket, so much that they were exactly opposite of each other at the bottom of the sprocket.

Has anyone else seen this before? I tried to find something similar on Google, but I failed to find anything. I should have taken a picture, but It was almost 2 AM Sunday and I wanted the car done. By the way, the car runs great now. I will rerun the compression test on the engine once the weather clears up. I noticed a vast improvement in all conditions after the timing chain job.

Thank you for any feedback.

 

I would need pictures to speculate on the cause but it sounds like it needed to go in the round file anyway. 208k is a great lifespan on a 1980's timing chain. My LB9 was pretty slack @ 150k and showing visible wear to the nylon sprocket teeth as well as some radial cracks.

GD

 

Are you trying to say, that the tooth/chain pitch is different between the new and the old?

Doesn't matter since you're changing it all out anyway.