OK poll on your theories, if you can explain your reasoning please do!

 

Increasing and decreasing strain on the TC from a slack condition puts shear stresses on the pins and elongates pin holes. These stresses are far greater than from a constant (non-slack) strain.
So far as I understand, the problem has been limited to manual trans cars. That would promote the theory because the manuals tend to create more shock to the TC than autos.

 

I have not voted but i honestly think the TC's on these car are either of faulty design or the lack of a proper tensioner device is the cause. Outside of the LSX world, NO ONE has issues with timing chains. You guys might site big hp as the cause, yet there are plenty of big hp F/I 4 bangers that use chains and wheelhop like there is no tomorrow without ever having an issue.

Its either that or these harmonic balancers are playing a roll in these failures. Perhaps V8's are subject to poorer harmonics as opposed to 4 and 6 cylinder engines. You also don't see any of the "other" crowd every changing their harmonic balancers....thats not a popular mod on any car other than an LSX from what I have found.

All I know is when you have a TC failure and no one can tell you what happened, you will question your desire to stay in a vette for fear of it happening again since you cannot pinpoint the problem.

 

I only know of one personally, and it was a stock chain that was reused after a H/C job, and in that same motor there were incorrect seats and a few other problems. I attribute it to installer error, not manufacturing defect, as I suspect may be the case in other failures I have read about. When I did my engine, the difference in slack of the new to old chain was dramatic, the slack would definitely have cause failure eventually if I reused it.

In overall assessment, with the thousands and thousands of LS series motors out there, there are very few reported incidents of chains failing...and since the damage is catastrophic, no one really knows if the chain failed causing damage, or other failure that caused the chain to fail. I think if the theory of harmonics, driver abuse, etc were true, there would be a lot more failures. Thinking about it, I can't recall ever reading about a stock LS engine's chain failing. Has anyone else?

 

Very well stated, after my second break we started to really wonder about the oil delivery system during high speed road course track days, and I started to wonder how long would I keep running a vette.

 

Well my break happened on the return road after a 1/4 mile pass. The break happened at 3500rpm. No roadcoursing, no engine breaking, no nothing. I was actually quite paranoid about TC failure prior to my failure and did what I "thought" would help prevent it. Apparently I didn't do enough. If I have another TC failure, a new crate LS3 will be purchased and the car will be sold. This issue is complete and utter bull****. Its a TC for heavens sake. On any other car, a TC discussion would never even arise unless you had 150k miles on your car.

 

How about all of the above plus a bad part.

Randy

 

 

With two breaks on stock blocks, I would be weary also George. You had a tough break there. (no pun intended)

 

Here is a somewhat interesting thread on the subject in road race section, the 05's have a TC tensioner, but it went away later on. I didnt pay attention to the split, but possibly 06.
http://forums.corvetteforum.com/auto...ls1-block.html

I will say that when a supercharger belt is too loose they tend to snap, so I cant see a TC being any different. However we really do not see too many failures normally, but we had a run on them last summer for some reason.

 

Engine harmonics/damper currently leading with aftermarket valve spring loads a close second.
What say you?

 

Harmonics are a crazy thing to pin point. You really need to have very high dollar equipment to find and fix the problem. So we trust the boys at GM to take care of this. But once a different balancer is installed, all bets are off. Most aftermarket companies aren't in the position to buy all these fancy tools to produce a good product. So it's a huge risk in my eyes to install anything other then a GM dampener. We use ATI's stuff because his experience and products have years and years of testing in race applications.

We had a brand new crate engine with 15 miles snap a chain crusing down the road. These are the biggest pains.

Spring pressure is needed in high power applications. But people get carried away with this too often. Or sometimes things just go unchecked which is even worse. Back when I was in the engine shop full time, I saw things you wouldn't even want to know about. 275 closed on a lightweight GM exhaust valve. Running a wimp of a camshaft without too much duration or lift. I shook my hand and said "drag racers". The best part about it the bind clearances were prefect for the application. Wrong spring was used in my eyes.

I have seen a rash of bent camshafts lately. Please guys and gals, buy good cams from good companies. I would say a bent camshaft would be extremly hard on a timing chain.

Good luck with your search
Randy

 

Spring tension cancels out the tensions on the opp side, however, a motor runs into issues when you use springs out of the box and dont have a matched set and then the opposing tensions do very much matter and it would make sense to then have the least amount you need as springs wear as Randy above says.

It is unlikely and unwise to think they will wear at the same rate and when was the last time you heard of anyone testing springs for wear after install 10 or 20k down the road. The flip side of using the least tension is that at a sooner point in age that they will not meet the demands of the application so lesser springs wont be usable for as long. Its in these applications that you hope as spring weaken that you have a valve that will survive an over-rev condition. At some point you will have too weak a spring. If one breaks then you will be happy you chose a good valve but thats a subject for another thread.

 

The spring canceling it other out, I will have to say it's not so. Look at a used camshaft with 30k miles. The opening ramps are more beat up then the following ramps. Plus when I turn over a engine on the stand, I can feel the opening and closing of the valvetrain.

I have checked a million springs in my days in the engine shop. They are pretty damn close out of the box, plus or minus 2.5 pounds at close. So we are talking about 2 percent on closed pressures. I have taken that to a new level on a few showroom stock engines. I have no idea if the spring tension matching is worth it or not. I can't see it hurting anything. A stock head has some "play" in it also. That is why it's very important to check the installed heights during spring install. Most people check only one intake and one exhaust.

Used springs get checked all the time around here. I just checked a set of 921 with 30k miles and lots of that were road racing. With in a few pounds of spec after 30k miles. We replaced them for a peice of mind, during a rebuild. I have worst presure drops in high heat applications, high rpm, huge race cams and etc.

Randy