Timing chain/plastic cam sprockets...IMPENDING DOOM...what to do about it...

[andre#4]

Has anyone changed their timing chain yet? or at least the plastic cam shaft sprockets that break?

I have not lost a tta motor in 300k miles, but I have lost 3 other gm motors from these little plastic teeth failing on the camshaft sprockets, which makes timing chain skip or stop going, then pistons hit valves. It has happened on cars younger than the tta, but they were built in 1968 and 1973.

I am obviously gonna do this surgery some day, but how soon do I need to do it? The only justification for not doing it right away is to say that maybe the plastic was better in 1989 than it was in 1973, and maybe the plastic can last more than 18 years (the age of the youngest car I had that imploded...this was a 1973 car that went bad after 18 years. Car just stopped running at a red light as if it had run out of spark. then motor was ruined bottom and top)

As much as I don't want to open up my virgin tta motor with 8k miles on it just to change a $20.00 item, I don't want pistons and valves to collide either.

Has anyone lost a motor because of this? How many miles on it and was it a race car?

Has anyone changed the thing preemptively?

I have preemptively changed about 4 of these things in my other gm cars that have the plastic cam sprockets.

I started doing it preemptively after losing 3 motors, as young as 18 years old, and as low mileage as 40,000. All cadillac 472" motors, which are otherwise strong, but the plastic sprockets are the same design as tta. Possibly with older plastic technology/chemistry.

Any thoughts?

 

[jarredsoon]

Cam gear broke on my car at 81k when I pulled the front cover I found plastic teeth at the bottom of the front cover. Lucky for me I was at home and had the car up on ramps to change the oil. Then started the car and backed off the ramps to level the car, turned it off tocheck the oil. Then the car would not start after that. Took for eeeeeever to diagnose that problem. I was checking for fuel and spark then compression etc.

I say do it!

 

[andre#4]

Be glad it didn't start. Could have been a problem...

On my caddies, when they cranked over I could hear that there was no compression. Or in some cases compression on only some cylinders. but by then the damage had been done of course. i always hoped the valves might have survived, but they never did. Always needed head work, and usually pistons too. one of the caddies is still in the yard 15 years later. It was not a convertible, so it wasn't worth fixing. A rust free low mileage caddy turned into a rusty mess right in my yard. Could you imagine a tta convertible sitting in the yard like that with a blown engine for 15 years. That would be something. That would never happen, but there is a 3000gt spyder out there. A somewhat rare car languishing, eroding in the weather. Oh well I don't have time for that stuff. Someday maybe. After my other more important projects are done.

And I was hoping everyone would say to leave it alone. This is not starting out very well. I'd rather sit on beechwood leather and drive than lean over a motor and remove parts! I was hoping someone would be a plastics expert and say, oh the new plastics are as strong as metal. But this, broken plastic bits on the bottom, this is no good. No good.

This may seem dumb, but what about all the wrench marks on the bolts I have to remove? I don't want wrench marks on it. it has never been apart. By the way, how does the factory put these things together without leaving little wrench marks on all the bolts? it is as if the bolts are born in place. They look new. But someone had to screw them in there. How did they do it? I can usually see when someone has taken something apart. Why can't I see the same marks from putting it together?

 

[jarredsoon]

I know what you mean about the marks on the bolts, I have new acorn bolts on my valve covers and they are painted black. I remove them so carefully to not scratch the black paint off. I think if you lube the bolt and gently place the wrench/socket on it wont mark them. Be sure to have the wrench/socket fully seated on the bolt head before turning so you don't strip or scratch the bolt. Hopefully that keeps them new looking and you don't slip off from the lube.

Replacing the timing chain should not take you too long if you have done it before, you'll be up and driving in no time.

 

[Quiky One]

Change it now. It isn't all mileage depedant, but age.

 

[PhillyTurboSix]

When I did the engine in my 86 GN it had a few teeth missing and massive stress cracks all around it. I guess they figured guys would blow the engines up long before they ever totally came apart!