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Old 06-10-2014, 08:16 PM   #1
theknave
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Default Guess That Noise (Videos!)





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Old 06-10-2014, 09:26 PM   #2
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Lacking any history or other information related to the sound, which would help immeasurably to pin point the issue, I'd say it's either a bad case of piston slap or quite probably rod knock.
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Old 06-10-2014, 09:32 PM   #3
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Exhaust manifold gasket would be my first place to look, then valve lash.
Was the engine cold in all videos?
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Old 06-10-2014, 10:04 PM   #4
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I bought the car at something over 260k miles. If I remember, it occasionally was tappy like this on a cold start. I think these videos are cold/warm starts. I'll post a hot start next.

I changed the spark plugs and had to tap one of the holes, cylinder 4. Some dirt and shavings got in there. I may have been over-handling the rusty exhaust during the procedure.

After this, the noise seemed more noticeable (louder) and persistent.


I've since fixed the hole and checked for blowby - there is none that I can feel.

I compression tested each cylinder, from 1 to 4: 160 psi, 150 psi, 150 psi, 140 psi.

I did notice exhaust with my hand coming out where the header meets the downpipe. I've replaced a missing nut there, tightened everything up, and slathered a good amount of exhaust sealer around the mating area. I no longer feel the exhaust coming out there.

One of the studs where the header meets the exhaust port for cylinder 4 practically fell out on it's own. Still the header seems pretty solid on the mating area with the head, and I haven't been able to feel any blow-by where the header does meet the cylinder head, but the air being blown by the fan may confuse checking for exhaust here. There's probably a good deal of self-sealing rust, lol. I've been thinking about slathering exhaust seal all over these areas.

The sound seems to me to coming out of the cylinder 2 area.

I recently checked the clearance of the adjusting discs/shims and here are the results:

Cylinder 1, exhaust: 0.014"
Cylinder 1, intake: 0.013"
Cylinder 2, exhaust: 0.016"
Cylinder 2, intake: 0.012"
Cylinder 3, exhaust: 0.016"
Cylinder 3, intake: 0.015"
Cylinder 4, exhaust: 0.016"
Cylinder 4, intake: 0.014"

All of these seem to be within spec, according to the Mitchell data I could get my hands on.

None of the tappets seemed unusual in appearance or movement while doing the clearance check, but I haven't taken the camshaft off yet to pull out the tappets to see what's going on in there.

Despite what I've done (sealing certain manifold areas, etc.), the sound has not been affected or changed in any way.

Piston slap or rod knock of course has been in the back of my mind this whole time, but a few other experienced wrenchers and technicians seem to say lifter/valves/tappets when they hear it in person because the sound does seem to coming from a little higher up.

The one thing I haven't done is changed the oil since the plug hole tap. I was wondering if that might help... put in fresh 10w-40, or perhaps even something thicker?

Last edited by theknave; 06-10-2014 at 10:12 PM..
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Old 06-10-2014, 10:45 PM   #5
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260k-ish when bought, how many miles on it now? Is it quieter or louder after it warms up? Is the car driven regularly?

I don't think the sound in the videos is related to an exhaust leak, doesn't really sound like a rod knock either, but sounds too rapid for valve train which is 1/2 the speed of the crank. Rod knock should be worse when hot. I remember something like: hold the throttle at about 3k rpm, let go and you should hear the knock slightly louder is it spins down. A more progressive rod knock will hammer a lot more when hot and climbing a hill.

Normal piston slap will be noisy only when cold; really bad slap will make noise all the time. Heavier oil will help quiet a rod knock. I used straight 50W in my '76 to get me from TX to VA, packed and over loaded to the point it cracked both frame rails.

We had an '90 turbo engine that sounded like an diesel at idle, cold or hot, sound seemed to come from down low, was like that for years. Took it completely apart and couldn't find the slightest thing unusual anywhere.
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Old 06-10-2014, 10:58 PM   #6
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Odo was broken when bought... from what I could glean from the previous owner, he seemed to say he put 10k to 12k miles on it, so I like to venture a guess at anywhere around 270k - 280k. I doubt I've put 5,000k on it yet, if so then likely right around there. I drive it at around 20 miles twice daily, have only had it 6 months, no road trips yet.

It seems quieter after it warms up, especially on a cold morning, but doesn't ever seem to go away completely.

Thanks for that info about the noises around rod knock and piston slap. I'll pay really hard attention to the sound in correlation to what you say above.

I'll also likely try heavier oil next time around, see how that goes, and maybe the oil change will help wash something out or something.

Your last bit there was a little more encouraging; my next question was, if it indeed was rod knock or piston slap, how many more miles would that mean this engine has left?


Also: If you think that noise is too fast to be valve train, my engine idles in drive/park at 840 rpm, 900-1000 while in neutral, according to my newly installed tach. The LH currently isn't getting a speedo signal, and I heard this may affect idling.

Last edited by theknave; 06-10-2014 at 11:25 PM..
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Old 06-10-2014, 11:26 PM   #7
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Piston slap is cosmetic, so no worries there.
More on piston slap here: http://forums.turbobricks.com/showthread.php?t=2298

Rod knock that loud, left unrepaired might go 1-2k miles, probably longer. Best to change your rod bearings asap, parts are not expensive, can be done without pulling the engine.
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Old 06-10-2014, 11:31 PM   #8
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The reason I asked about the mileage is if the sound showed up suddenly/recently, I'd be worried, if it's been around for a long time, most likely it's piston slap. It's unlikely the spark plug hole repair was unlikely to have caused an issue, but may have improved the efficiency of that cylinder, possibly exacerbating the piston slap.
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Old 06-16-2014, 05:31 PM   #9
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Here are some more recent videos.

This one may be the most informative of the bunch. This is a cold start in the morning. The noise is quite definitive initially, but dies down after about 30 seconds. I rev the engine a couple times to notice a difference, but revving doesn't seem to create too much of a difference in the noise, I think...




The following are all hot engine, in the middle of the day after a freeway run. The noise seems lessened compared to the rest of the videos in this thread. In these videos, it seems the most pronounced noises are injector ticks and regular old upper end noise.








Some thoughts:

- Noise seems most pronounced on cold starts, when ambient temperature reaches or goes below 60 degrees F.

- Car is typically parked angled front-upward due to inclined parking space. Last night parked it head in, angled down toward the front, to see if where the oil settles in the pan overnight makes a difference. I'll include that information next.
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Old 06-16-2014, 05:47 PM   #10
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Put a real oil pressure gauge on it and see what the pressure is. It could be that the oil pump transfer tube o-ring is bad.
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Old 06-16-2014, 06:50 PM   #11
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Will do. That's been something I've been wondering about trying. I did notice a severed wire, which I'm pretty sure is the oil pressure sensor wire, severed right at the sensor. That sensor couldn't set off a warning light if it tried.
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Old 06-18-2014, 03:40 AM   #12
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The initial noise is definitely piston slap on startup. The continued noise once it is warmed up sounds more like a knocking rod, but its really hard to tell.
I would get a mechanics stethoscope. Listen down low and in the middle of the block. It will be pretty obvious where the noise is the loudest. If it is a knocking rod, it'll all be down low. Rod knock also tends to sound louder under load (driving up a hill) for obvious reasons.

Either way, your motor is at the end of its useful life as it currently sits. Compression that low (140/150 for a NA motor is really low) combined with slap/knock means that you should be looking to rebuild or find a lower mileage motor to pop in there.

I definitely agree on the oil pressure gauge.
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Old 06-18-2014, 12:07 PM   #13
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Man, I've been hearing a variety of things from people as to the causes of the noises, I tell you what.

I've used a stethoscope. Sounds are loudest right at the valve cover, and at the exhaust manifold particularly the EGR return pipe. I'll listen again, really focusing on down low on a cold start.

Two experienced mechanics and instructors have heard it in person, one with a stethoscope, both insist on upper end noise. This has typically been when idling, however, when warm-ish (not hot).

Yesterday, I put in fuel injector cleaner with a entire tank of 92 octane, poured half a quart of Lucas Oil into the engine. The noise definitely subsided a quite a bit.

I do hear it more when entering an shallow incline. Quieter most other times.

I'm open to whatever the cause truly is, just trying to avoid unnecessary decisions, of course.
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Old 06-18-2014, 10:08 PM   #14
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Valvetrain, for sure. The cold-start video is the giveaway. Change your oil with proper viscosity, check your oil pressure. Perhaps there's valve guide slop. Meh. Sounds like a normal old redblock. Bottom end problems seem to sound worse as the motor spins up and/or is under load, not particularly at idle, as yours to be at its "worst."
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Old 06-19-2014, 08:14 PM   #15
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Alright dudes, here're the results of the pressure test:





I heated up the engine, drained the old 15w-40 Castrol dino/Lucas oil stabilizer mix, added basic 10w-40 dino and then ran this test.

Then took it for a test drive. It sounded decent, better than yesterday. Keep in mind this was all on a pretty stinking nice Seattle day (Mostly sunny/blue skies, 79 degrees).

Before this test, when I first started the car, I used the stethoscope some more.

Noise was most pronounced right on top of the valve cover right over clylinders 2 and 3, on the exhaust side of the "Volvo" lettering.

Again, the EGR return pipe was also loud.

Lower down on the head and in the block was pretty quiet. The only place I was able to hear noise was when touching the stethoscope to the oil pan, and in this case it sounded a bit like the noise from the valve cover.

A note about the 140 psi cylinder: I tapped that spark plug hole. May not have been my best tap ever.
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