I searched "knock 3.6" and got zero results.

I'm looking at an XR, 118k, absolutely pristine condition, and multiple indications that it's been well maintained, though I won't go into details in hopes of keeping this short.

It has a definite knock. Not the "can of marbles" rattle of a timing chain, but also doesn't seem like a rod. It has a different tone. In my experience a rod knock is like a 3lb hammer on a railroad track, and a lifter knock is like an 8oz ball peen on a metal valve cover. It sounds more tinny, like a lifter. But given the valve train layout, it can't be a lifter.

Owner says he did try to get codes out of it and got a "random misfire" code. I pulled the plug off each coil, one at a time. The noise didn't change, and the engine ran noticably rougher each time, so it seems obvious it's firing on all 6.

Best I can tell the knock is coming from the rear bank, middle cylinder, top end somewhere. Any common issues I should look into that would cause this? Any thoughts on narrowing it down?

Thanks

 

I was doing more searching, since I've never worked on one of these engines. I saw a few posts online about how this OHC engine doesn't have lifters, and I have worked on other OHC engines where the cam sits directly above the valve stem, separated by a bucket style "lifter" with shims. I assumed that's how the 3.6 was set up.

I saw Rock Auto has a listing for lifters and valve springs, so I'm assuming there's some kind of rocker arm arrangement under the cam, with a hydraulic "lifter" on one end, valve on the other?

I'm not familiar with this engine, and not finding decent pics online. I'm guessing it's possible to have a collapsed lifter.
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According to Wikipedia, that engine was also used on the Cadillac CTS, I suspect on the 2007 and earlier models. Saw a lot of videos on YouTube on timing chain, tensioners, etc. on Cadillacs, but not much on rockers, lash adjusters, etc.

 

I
I would pull the back cam cover and take a look. The wheel on the follower could be bad and the cam lobe or just the lifter. You will be able to see if the oil has been changed on time.

 

Based on papers and stuff in the car, as well as the overall condition, and conversation with a seller who seems trustworthy, I'm assuming the oil was changed regularly. Of course you never really know, but sometimes you get a sense that your dealing with an honest person.

The problem is, I haven't bought the car yet. Apparently he's had a couple people look at it and tell him it needs an engine. Could be it does, or could be they're just trying to get it dirt cheap. Or could be they have no idea what they're doing. The sound is very distinctly from the top end, but having said that I did see a video on YouTube of a LaCrosse or something that had a top end knock that turned out to be timing chain related somehow. VVT sprocket or something, I don't recall.

Initially when I posted I had very little knowledge of this engine. I've read and watched a lot since then, but still know little about it. I was hoping I'd get something like "Oh, yeah, collapsed lifters are common on that motor". No such luck. And given that the owner seems to have kept the car meticulously, I'm surprised a lifter would fail. However, I also saw a video on a well maintained engine that was spotless under the front cam cover, but had a bunch of gunk under the rear cam cover. Something about the PCV system. Maybe that caused a lifter to fail, I don't know.

I just don't want to buy it and find out it does in fact need a motor. I'd have no issue doing the work, it's just that I've got multiple other projects and don't really need another. Maybe I'll just have to take the chance because it really is in pristine condition other than the knock. As mentioned, that engine is in lots of other cars, and I did see mention somewhere of somebody swapping in an LLT engine and all the associated direct injection parts / wiring / fuel pump. Never actually saw a build thread on it though. Just a rumor, but an intriguing one.

 

Some engines are very dependent on the PCV system. Maybe the owner never serviced it and that's what's caused the knock. IDK, just speculating. I'd check the PCV just for the heck of it and see if it's operating properly.

 

Chrysler 3.6 is notorious for cam follower/ lifter failure, the dealers keep the parts in stock. There is not great knowledge in the Saturn forums due to the short run near the brands demise. You might find a deeper knowledge base on a different GM forum. I have never worked on any of the v-6 engines newer than the 3.0 L81.