What actually causes a timing chain to go bad?
 

What actually causes a timing chain to go bad? Is it just the nature of the beast?, age, driving technique? etc.,

some would say the parents are to blame, while others would argue that society is at fault.

As for me, I think you really need to point the finger at the (insert political party of choice here). Their insane policies make it impossible for a timing chain to live a good and decent life.

Ahh...but what about the environment?
The inner city chains are at a disadvantage ....the country chains have better air.....
Bob

Thanks for the laugh Todd

Seriously, chains stretch...eventually enough so that their links don't meet up well with the sprockets they are supposed to align with. There is a method for measuring stretch, but I'm not sure what it is.

Can this "stretching" factor be influenced by certain driving habits (eg acceleration, shifiting at certain RPM, or other factors ?? ) Or is this from the quality of the materials themselves perhaps?

Wear; I do not believe chains are ever normally loaded enough to yield the steel and cause plastic "stretch". What happens is the mechanical elements (links, rollers and pins) rub on each other as the chain moves over the wheels or sprockets. Because lubrication isn't perfect and oil has dirt and swarf in it, this rubbing removes a small amount of material from each pin and link over the life of the chain. This wear increases the clearances at each mechanical element and the connections become looser and this makes the change effectively grow in length and only appear to stretch. Wear on the chain wheels or sprockets has the same effect. Jim

Thanks Jim.

HawgRyder gave a good thread on eyeballing the chain & sprocket between 2 & 3 weeks ago................Ron

Timing chains WILL stretch if the manual chain tensioners are used and over tightened. The good thing is, these chain tensioners were mostly used on race engines and not usually found on street cars.

Also chain wear can be measured by measuring x links of old chain and comparing to the length of x links of new chain. Unfortunately, I don't know if Porsche specified this difference or chain wear specs.

I don't know how much tension timing chains get, but for an anology, on a bicycle if you ride it regularly you should get a new chain 2 times a year. When it stretches, it will wear out the cogs and chainrings prematurely. One method of testing the chain for wear is to measure the distance between a number of links. a worn chain will be noticeably longer than a new.

Swarf?!

Swarf is residue left by passing Smurfs.
And yes...chains do stretch....law of physics.
Old rule from motorcycles is: 2 chains to 1 sprocket.
This means if you replace the chain twice...you should replace the sprockets the second time.
However...if up to me...I would replace the chain and sprockets at the same time for longevity.
On a bike...it's not too hard to get to the sprockets...on a P-car...the engine has to come apart....soooo....while you're in there!
Bob

Chains do stretch. Anyone who owns a motorcyle for more than 10,000 miles know that they stretch. Same for timing chains, except that they take much longer because they only have to pull the mass of the timing gears (100lbs), not the mass of the entire motorcycle plus rider (600lbs)

It's probably only a difference in semantics but becoming longer through wear is not the same as plastically stretching. The higher the load and the dirtier the environment the faster a chain wears and appears to stretch.

Nope. They don't stretch. The hinges at each joint wear loose. This makes the chain longer, sure, but it's not stretched. Its hinges are loose.

Since the chain does not fit the sprockets well anymore, the sprockets wear in an asymetrical fashion. Kinda teardrop-shaped. I didn't see Bob's earlier post, but I'm sure it's revealing.

MC chains are hanging inches from the road and wind and water and dirt. The front tire is probably splashing it with grit. Not so with our timing chains. They are replaced at rebuild time, but they last a long time and very rarely fail.

they stretch. imho.

i would be very surprised if "wear and tear" were the cause of the increased length of m/c chains. they can be used in excess of 15k miles - they would be in a pretty sorry and dangerous state by then -wouldn't they?

btw - "Since the chain does not fit the sprockets well anymore, the sprockets wear in an asymetrical fashion. Kinda teardrop-shaped"

not true on a m/c. the smaller front sprocket only goes like that.

Well what ever it is? stretch or wear I learned at an early age what happen's when their loose and have the scar on my chin as a reminder.
Power runs and loose chains don't mix :D It was an air cooled Schwinn Stingray, I did a swan dive over the bars when the chain came off.
It was pretty dam fast too :p So keep your chains tight and your powder dry, but not to tight.