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June 5, 2011 9:34 PM   Subscribe

Car geeks: I'm having trouble identifying this knock [.MOV on Dropbox] in the engine of my 1991 Dodge Spirit. It sounds a bit like a clicking sound, except it turns out to be a wheeze when it gets worse. I've just replaced one of the valve rocker arms because it turned out to be broken. I also Do you know what might be causing this?

I can give more details – for example, I've just changed the oil, and I checked the plugs and they seem to be firing fine – but I have a feeling that sound is distinctive enough that some people will have ideas.
posted by koeselitz to Travel & Transportation (18 answers total) 2 users marked this as a favorite
Response by poster: Please ignore the "I also" above... I'm a bit tired.
posted by koeselitz at 9:37 PM on June 5, 2011

Still waiting for the video to download, but are you sure it's not valve lash?
posted by bodaciousllama at 10:39 PM on June 5, 2011 [1 favorite]

Response by poster: Hrm. What's valve lash?
posted by koeselitz at 10:44 PM on June 5, 2011

Disregard that, your sound is waaaaay too low.

Valve lash/tap is when there is too much clearance between the rocker arm and the valve so it starts tapping, but it's a higher pitched sound, like this.

Since you replaced a rocker, I'd check the clearances again with a feeler gauge. Specs should be somewhere on the internet, or in a shop manual.

The sound is periodic, so there could be something wrong with the combustion process on one cylinder. The worst scenario that I can think of is a shot connecting rod. But I don't know of any easy way to check without taking off the oil pan and seeing if some metal falls out. Maybe a compression test may reveal the cylinder having issues.

As always, IANALicensedMechanic
posted by bodaciousllama at 11:01 PM on June 5, 2011 [1 favorite]

Also, check the oil level, remembering that too much oil can also cause damage
posted by bodaciousllama at 11:05 PM on June 5, 2011

Response by poster: Yeah, I don't want to blow a gasket by having too much oil. But I seem to have just the right amount; checked on that.

So your guess is a problem with the combustion process on one cylinder? I guess I'll replace the plugs tomorrow just in case. I'll assume the shot connecting rod as the worst-case scenario. I also would rather avoid doing a compression test – I don't have a gauge, and I'd rather not pay for the test, but we'll see.

What else do you think I should do? I'm guessing the next step is to check the injectors, right?
posted by koeselitz at 11:11 PM on June 5, 2011

The plugs shouldn't have to be replaced. Check out the injectors first. Some people pull them out and then fire the engine to see if fuel sprays everywhere. It might be smarter to use a ohmmeter.
posted by bodaciousllama at 11:27 PM on June 5, 2011

An ohmmeter will only tell you that the winding of the injector solenoid is OK; it won't tell you if the injector is stuck open or closed. But for an initial test, yeah, with the proviso that it's not really testing whether the injector is working properly or not.

But, afaict through the restrictions of the video, that sounds a lot like blowback into the inlet manifold / air intake. Which rocker was broken - inlet? 2nd'ing double-check your valve clearances (you'll get blowback like that if it's way too low); also double-check it against an adjacent valve (of the same type - inlet or outlet) to make you're not misreading the specs / adjusting it wrong. Other causes can be a stuck lifter (though it's an overhead cam by the look of it, so probably not that - but maybe a sticking rocker?) or a burnt/cracked/damaged valve or valve seat.

It sounds a too slow to be a shot conrod / bearing, misfiring sounds different, and pistons sound worse than that, so I'd put them to the bottom of the list for know.
posted by Pinback at 11:55 PM on June 5, 2011 [1 favorite]

Response by poster: I haven't adjusted my valves at all because I'd rather not remove the cam; but if I have to, I guess I will.

At this point I'm just going to check the injectors. I'm really hoping I don't have to take the cam out to adjust the valves and such, as that's a complicated job that I'd like to avoid, but maybe I will have to. My rough check of the valves made it seem as though they're all as tight as they should be, but maybe I was wrong.
posted by koeselitz at 7:41 AM on June 6, 2011

It's probably not vales or injectors - doesn't sound right and frequency is wrong for engine speed. If the car has an air pump look at that - look at the connections. If the the car has an EGR valve look at that, but generally, when those fail the car will not run as well as you car is running. Finally, the I couldn't tell if the AC compressor was engaged from the video, but check the connections to that as well.
posted by alfanut at 9:10 AM on June 6, 2011 [1 favorite]

Take off the air cleaner. It kind of sounds like one cylinder is backfiring through the intake.

That engine uses hydraulic lifters (I am pretty sure), so adjusting lash shouldn't be necessary or possible. Regardless, it wouldn't sound like that.

Shouldn't be injectors, because that's only got one (unless you've got a Mexican or turbo, if I remember correctly), and the injector isn't big enough to make that kind of sound.

Are you sure you got the right part for the rocker arm?

Are you sure the valve isn't damaged?

Are you sure the timing belt hasn't jumped a tooth or two?

Anyway, what I hear is both misfire-y sounding and mechanical damage sounding. Especially if the relative volume is what it sounds like in the video.
posted by gjc at 9:32 AM on June 6, 2011 [1 favorite]

If that's the 2.5, there is a balance shaft in there somewhere. I forget what it drives off of, it is possible that it could have gotten out of time with the engine.

Also, enjoy.
posted by gjc at 9:38 AM on June 6, 2011 [1 favorite]

Response by poster: Thanks, gjc. I actually noticed that one of the hoses coming off underneath the air clearer is ripped clean through; going to have a go at duct taping it tonight and seeing if there's anything else a little off down there.

It's the 2.4 engine, actually. Maybe a timing issue, though? I'm sure I got the right part; it looked exactly the same as the other rocker arms, and it fit snugly. Also, it seems to have stayed where it was, working properly, all through me running the engine yesterday; so I don't think it's that.

My biggest worry is a damaged valve. I am not sure that that's not what it is, but I don't know any way to test that without a pressure test. I guess I'll have to get one of those if I can't sort this by fussing with the air filter or adjusting the timing.
posted by koeselitz at 12:35 PM on June 6, 2011

This might get messy, but it ought to work in a pinch. Take off the valve cover and run the engine, and see if you can pin the noise down to one of the timing events. At idle, everything is spinning slow enough that you should be able see what's going on.

Upon further review, the clunk happens once per revolution of the valve train. (Or once per two revolutions of the pistons.) So it likely isn't a bottom end issue, or it would happen twice as fast.
posted by gjc at 5:31 PM on June 6, 2011 [1 favorite]

Response by poster: Hrm. "Bottom end?" You mean on the bottom of the valves?

It looks like the hose coming off the air filtration unit is torn clean through. Since it's sort of loping, and because of the wheeze, my guess at the moment is that torn hose coupled with a timing issue stemming from when I replaced the rocker arm.
posted by koeselitz at 6:08 PM on June 6, 2011

Sorry, by bottom end I mean pistons, crankshaft, connecting rods, bearings.

Did you try running it with the air cleaner removed?
posted by gjc at 7:07 PM on June 6, 2011

SO, any news?
posted by bodaciousllama at 5:25 PM on June 8, 2011

Response by poster: Thanks for asking - meant to come in today and give an update.

So: first the good news. I'm pretty sure I've fixed the initial problem - and it was much more obvious than I'd thought. I opened up the valve cover again, and what do you know - the rocker arm had popped off again! I'm pretty sure that this means that when I get it to my new place (I'm moving this weekend) my next project will be to adjust the valves. Even though it seems quite solid now, I guess there must be some looseness if it's popping off like that.

At this point it idles quite nicely; clean, smooth, pretty quiet, and above all no clicks or knocks, which makes me very happy.

However, there is still some trouble.

When it's idling or driving, about every three minutes it does two things: it begins to emit a few puffs of smoke or vapor (looks more like a vapor, actually) from just behind the valve cover and underneath the air cleaner; and it starts to run down, wheezes a bit, and either dies or comes close to dying. Then, if it recovers, it runs fine again for the next few minutes before this happens again. The engine doesn't appear to be overheating really, and there isn't much snake/vapor; but this worries me.

The air filter is relatively new, so I don't think it's that, but I was thinking this might be a vacuum problem. The other possibility I'm considering is a bad fuel filter or something clogging the line a bit.

This is a car, I should say, that sat for about six months without being driven. I've changed the oil and replenished the coolant, and other fluids look good. I keep thinking this must have something to do with the car sitting so long.

Does anyone have any thoughts on what might cause this problem?
posted by koeselitz at 5:36 PM on June 8, 2011

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