Premature Timing Chain Wear

Nick1994

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My grandpa has a 96' Jeep Cherokee 4x4 4.0L. It's been amazingly reliable and the only repairs over the past 7 1/2 years and 35k miles have only been a leaky radiator & water pump, fan clutch, and the rear main seal. Lately it would act like it was running out of gas for just a second, kind of cut out. It would then not start and act as if it had no spark, but it had fuel then it would start the next day. My grandparents next door neighbor is a great mechanic (a good buddy of mine) who we had look at it and it had a check engine light code for a cam position sensor. He took the distributor cap off and the shaft was really wobbly on the distributor which caused the rotor to chew up the cam position sensor. After replacing the distributor and the spark plugs and wires it ran great but then would stumble randomly again and set off another check engine light code - engine misfire. The neighbor mechanic looked at it again and said the timing chain was worn. When turning the crankshaft pulley it would not turn the distributor shaft until the pulley was turned to 19 degrees before TDC (I believe it was before TDC) and had lots of slack. He's in the midst of changing it now, but after taking it apart he said it had LOTS of slack in the chain and the tensioner in there was toast and the teeth on the sprockets were worn down pretty good. The Jeep has always run what I consider as fantastic, tons of power and pretty smooth but it has always had a slight "miss" at idle that's almost unnoticeable unless you're paying attention. After replacing the distributor the miss went away I'd say about 90%. I'm kind of anxious to see how it is with the new timing chain. I'll go by tomorrow and see it. This Jeep was owned by the Arizona Department of Transportation for the first 11 years and nearly on the dot 100k miles of its life, I assume it was well taken care of, it pretty much looks like brand new. I changed the rear main seal and oil pan gasket last December and the engine was absolutely spotless, it looked like it was a brand new crate motor from the underside - really! It's now getting some PPw/PP and a Fram Ultra filter, quite a bit overkill since it only gets maybe 2,500-3k miles per year on it but that's alright. So my question - What would cause the timing chain to wear this early in life? Thanks.
 
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My uneducated guess says once that tensioner goes rapid wear could be next due to the chain rubbing on the case or too loose on the sprockets (teeth-chain wear).
 
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It does not use a tensioner or guides.just 2 gears and a chain.I have never seen one that needed a new chain and gears. Ever! I'm guessing that it may have tons of idle hrs over the milage
 
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Those timing chains hardly ever fail, and as mentioned they don't use guides or a tensioner.
 
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It's eighteen years old and you wonder why the timing chain is worn? Look at all the wear points in a chain. A very small amount of wear at each point adds up to enough wear to require replacing. From what you have posted, I would say you and Arizona got your money's worth.Regards
 
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I was expecting a thread about a newer vehicle. Maybe something from this century smile yikes 18 years old I'm not sure counts as premature.
 

Nick1994

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It actually wasn't my mechanic buddy who told me the tensioner was worn but his helper, I don't know I didn't look at it. I say premature wear because I thought timing chains were for the life of the vehicle? Yes it's 18 years old but has low mileage.
 
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timing chain will stretch over time due to stress/load/thermocycling, as well as wear. Timing will becomes off as time goes by. timing chain will becomes noisy as they become worn/stretched. Most timing chain configuration exhibits more wear and failure on the tensioner part, regardless of design. Cost for timing chain replacement can be high, for you need to consider a full timing chain set, chain tensioner assembly and sprocket sets. Labour costs would be much higher due to the complexity of hiding more stuff behind the cover, etc. Timing belt, on the other hand, exhibits less timing deviation as it ages, and will be fine until it breaks. timing belt does not get noisy as it gets older. timing belt replacement is considerably less to that of timing chain, due to the lack of sprocket set replacement and also the extra added labour cost associated with timing-chain related RE-n-RE side. **************************************************************** In summary: timing chain and timing belt both have their strengths and weaknesses, and my take is that either of them serves their purpose well until it's time to replace/service. Most posters here are taking on the stance based on sentimental reasons. Q.
 
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