97 Cobra engine rattle at mid RPM

[Rokgtar]

Hello, I have a 97 Cobra, 142k, all stock, does not smoke or burn oil, starts up and runs great, plenty of power, plenty of oil pressure (according to the stock gauge). Recently it has developed a rattling sound in the mid rpm range (3-5k) that i am trying to get to the bottom of. Initially I suspect the timing chains/tensioners, but I am not 100%. I am taking it to a shop (tomorrow) for a diagnosis. Bottom line - I am afraid I am going to get screwed. I know the dual timing chain layout and how the tensioners and the guides work, but I have seen prices for the whole timing chain kit for like 600.00 plus. Add in the labor and I'm probably looking at well over a grand to pay someone to do the work. I could probably do it myself (hard finding the time) with instructions, but I'd feel better having someone who does it often do the work. I've used the search function on this site and have not really seen a lot dealing directly with this issue. Maybe I'm not searching correctly... Can any of you give me your thoughts on what other things could cause this sound, how hard it is to replace these parts, the cheapest places to get the parts, etc..., what I should expect to pay for a shop to install this for me? I am on a budget and this car really runs well. I want to keep it running good without a rebuild and/or a replacement engine for as long as possible. This car is not a daily driver but my hobby car. I don't have any plans to race it, etc... just maybe lowering springs and/or a 4.10 gear. Any help/advice/possible other causes that any of you can offer would be greatly appreciated. Thanks...

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[Smokin04]

Make any timing adjustments recently? Also, can you pinpoint where the sound is coming from? Is it in the heads, or on/near the block? Does the rattle increase/decrease with RPM or does it have the same pace while audible?

[Rokgtar]

Thanks for asking... It happens after it warms up (after a ride), and it does seem to speed up/slow down as I rev the engine.

[marcuskeeler]

Does the noise of the rattle become more intense if the motor is under load? When you're driving and get to the "rattle zone" let off the gas, does the noise go away?

if the noise is constant and is only a function of RPM and not load related, then it does sound like a timing chain issue or valve train. If it varies in intensity according to load then I'd say you are looking at something in the short block department.

[Rokgtar]

OK... I took the car in to the shop and they say it is definitely in the top end of the motor. It seems to occur in the 2k rpm range, disappears beyond that (I think) and it lets up when I let off of the gas. They said it might be a lifter sticking... They said it runs great otherwise and that they would not do anything - a motor with 142k on it is bound to have clatter in the valvetrain - just keep it maintained and drive it.

That being said, this is not a pushrod motor... so - does it even have lifters?

Another question (my experience is with pushrod motors) - can the rockers be adjusted? Could it be that I just need to have someone adjust the rocker arms, something else in the valvetrain, etc...

Thanks again everyone...

[Smokin04]

Yes and no. You do have a lash adapter which is similar to lifters in a pushrod motor. They are hyraulicly operated and it is possible for them to fail and collapse. 142K miles I wouldn't be surprised if that was the culprit. Good news for you. They're about 20 bucks, but just labor intensive to install. Might as well replace all of them.

[ARdoller]

have you tried cleaning the IMRC plates?