I've finally got the chain out and found something unexpected... One of the pins was sheared in half?? I haven't seen any cases in my research where this occurred.







From what I can tell it appears to be the stock chain. The section that failed has one darker link which makes me assume that it's the 'master' link. The link with the missing half of the pin has a stretched hole which leads me to believe that the pin either pulled through and then broke, or it broke, walked out and then got torqued.

The links at the failed pin are not as flared as other cases I've seen which leads me to believe the pin split before the chain came apart allowing the separation to occur with less pressure on the links.

The damper also appears to have slight markings, but they might be normal. On the side of the crank sprocket where the chain ended up piling up there is a wear mark. Either the broken chain made that mark after piling up there, or the pin walked out and started rubbing. Since it's only present on one side and doesn't appears to be scored multiple times I'm thinking that it was the chain piling up.



Based on everything else I've seen in the valvetrain my best guess is that the chain stretched, developed slap and failed. When I placed the chain on the gears it did seem loose, there certainly was room for it to impact the damper.

Please comment/speculate, but keep the arguing to a minimum!

 

Excessive tension in the chain from running a big cam with heavy springs?

 

Appears that the pin wasn't peened over enough to keep it in place.

 

I think the peened part of the pin was sheered off. To the OP did you find the little piece that got sheered off?

 

No, it did not come out with the drained oil. I'm sure it's in the oil pan somewhere, but I can't see it. Maybe next time I drain it? I'm a bit worried to rebuild without finding and removing it.

 

All I can say is, Damn.

 

D'Oh! That blows

I would definitely figure out where that missing piece is before putting her back together

Best of luck

 

YES! Definately make sure you find that little piece before putting it back together. If you have already drained the oil and did not see it I would get a screen filter and filter the oil to see if you missed it. Might need to drop the pan as well.

 

Can I ask if the chain was replaced when you did the cam? What are miles on the motor and do you have a aftermarket pulley?

 

I think the pin pulled through and then failed. Another member last month had a similar timing chain failure that I said the same thing about...it appeared the pin wasn't peened over enough to keep it in place and walked out of one side causing too much stress on the one remaining link. In his case, the link failed, not the pin. The really interesting thing is the bend you have in the link the pin is still in looks exactly like the bend in the link his pin was in on his chain. I'll see if I can find the thread, the member is "1.8t".

PS There is no master link. A master link is designed to come apart to enable removal of a chain that has to go around a frame for instance...like a bicycle or motorcycle. All of the links on your timing chain are peened over.

Edit: I found the thread. http://forums.corvetteforum.com/c6-t...-pictures.html

 

this is about the 3rd post i have seen about timing chains breaking over the last 6 months. All share similiar things, cam changes and/or head changes. Alot of guys will blame the chain as your problem. I wont begin to get into an argument and try and say they are right or wrong.

But will tell you this, as an ASE master technician i have never changed a broken chain on a small block chevy. Some stripped gears or maybe a loose chain but never just broken. My good friend who has worked as a master technician at a chevy dealership for the last 20 years has also never changed one out that was broken.
Take that for what its worth,,,rea lworld info with a combined 35 years of experience,, There may be a rare case out there of a failure on a stock engine but i have nvere heard of one. I am only posting this info for one reason, i could care less whether anyone agrees or not but to merely blame the chain and not look into other possible issues would be in my opinion a mistake you will regret. I am not looking to be a target to go after only trying to assist you in your issue and hope that it doesnt happen again. I dont think you will find even "one case" of a failed timing chain on this forum where the engine was stock. What could have cause this? look to the parts you put on aftermarket wise, heads springs, cam etc.. and go from there. Good luck on your issue and i wish you the best on fixing your ride, it stinks when they are down.

 

Unfortunately, some of us only "hear" what we want to hear.

 

Do tell???

Modifications have killed more engines, transmissions, rearends, and outright cars in here, than than DDT has killed cockroaches.

 

Best of luck with getting it back together. And some people still question why GM voids the warranty when we mod our cars.

 

I agree with you, the extra pressure of the cam and springs were most than likely the main factor, but regardless, the chain was the failure point. I'm not blaming the chain as it was not intended for that purpose. It should have been replaced with something that was intended to take the additional stress.

 

Spring tension is irrelevant. Opposing springs cancel out the tension for a sum-net-zero.

Power is the thing that kills a chain and its why the LS2 breaks them and LS1's dont. The average power is up with so few people running stronger chains. I laugh when people talk about resonances with UD pullies. They are the same pullies with the same cranks as the LS1.

 

Spin, I would tend to agree with you. The only problem I see with that theory is that I have yet to hear of a C6Z w/ bolt ons fail because of TC failure. Hell, I have yet to hear of one with a cam fail because of TC failure. Now, we all know that bolt on C6Z's can make 500rwhp and ones with cam's can go 550+. Supposedly they are using the same chain correct? Perhaps there have been a numerous C6Z TC failures, but if so I have yet to hear of them.

 

This is a good point, if in fact the Z's chain is the same. Two of the more well documented cases, yours 1.8t and welcome2try, had variables other than just more power that may have contributed. I believe yours was a possible manufacturing defect in the chain itself, correct? Welcome2try's breakage was due to faulty/incorrect parts in the valvetrain from improper install. His was also and '05. I had heard that the '07? chain was slightly stronger. Can anyone confirm that? I don't believe an UD pulley is the cause however I feel it's more than just simply more power or else I think there would be a lot more stories like these. That being said it's silly not to upgrade the chain when doing a cam swap. Have there been occurances of the aftermarket chains breaking? If so does anyone know the cause in those cases?

 

I disagree with the hp rating of the motor doing anything to the chain. From 300hp SBC to 1000hp BBC, they all use the same types of chain made by the same manufacturer (I like cloyes myself). There's no HP ratings on chains/belt drives, because it's a no factor.
Now, have something bind and you'll break it or the gears.

 

And the harmonics are diffferent for the LS1,2,3. There is not a known answer currently or those who do actually know are not saying.