2015 Peugeot 308 - Severe vibrations after maintenance, mechanics are at loss

Very interesting that replacing the H damper ended the vibrations for one day, but then they started , slowly at first, again. Are you certain the current vibration level hasn’t always been there even when new, but just went unnoticed b/c ? If not, seems like the next step is to replace the H damper again. Buy the replacement from a different place than you bought the most recent one, in case they have a bad batch. It’s possible the replacement was installed incorrectly as well. There’s usually a keyway that has to match up, then it has to be tightened the correct torque, which isn’t always easy to do b/c the engine wants to rotate along with the bolt. Might try standing sideways to the engine compartment and watch the HM from the side, engine idling. Might be easier to see from below, eye protection whenever looking upwards of course. See any wobbling?

Hi George, thank you for your reply.

The mechanic assured me that the new harmonic damper has been precisely torqued according to the proper spec, and that there wasn’t any room for installation errors. Judging by a visual inspection it doesn’t seem to wobble at all.

Today I’ve asked the mechanic to perform a final test: letting me drive the car with the serpentine belt detached, thus excluding the alternator and the a/c compressor pulleys as culprits for the vibrations (the water pump pulley is driven directly by the timing belt). The vibrations, albeit dampened, still persisted, especially in the lower part of the car, pedals and gear stick.

The entire car shakes at ~1400-1500 rpm, while above 3000 rpm it’s butter smooth.

The mechanic said that probably something bad happened inside the engine, but it’s skeptical about solving the issue with a timing chain and water pump replacement. OBD diagnostics are still negative.

I’m starting to believe that an exorcism is the only recourse left…

What does the mechanic offer as a plausible explanation for the vibrations almost completely disappearing for one day— post replacement — then they started again the following day, for no apparent reason? Imho, that sequence most likely indicates a problem with the replacement part or the installation. From reports here, you definitely wouldn’t be the first to get a faulty replacement part.

The mechanic hypotesized that the crankshaft itself produces those vibrations (maybe because of a failed bearing or an issue with the injection that the ECU isn’t able to detect), and the serpentine belt in full tension helps stabilize it for a few hours after being detached and reattached, then when it starts to give in and have tiniest bit of slack it doesn’t hold the crankshaft pulley tight enough anymore and allows it to vibrate.

I’m also hesitant to believe that the replacement harmonic damper is at fault, as the vibrations - albeit lessened - persist even with the serpentine belt detached (which I admit doesn’t make that much sense, if the “tight serpentine belt doesn’t allow the crankshaft pulley to have enough play to cause vibrations” theory holds true)…

Said that, after all those parts were replaced, it may also be true that the original vibrations have been eliminated and the persisting ones are caused by one of the new components, so I’m pretty much back to square one.

I wish Tom and Ray could have heard this explanation, would have been great radio! … lol … I guess it’s possible, but seems pretty unlikely. The crankshaft’s bearing clearances could be measured to prove or disprove this theory. It seems like a mechanic would also be able to measure the crankshaft pulley in and out and up/down play using a dial indicator without too much difficulty.

Another idea, I think you mentioned this car has a manual transmission w/clutch. When you press on the clutch you are also pushing on the crankshaft. There’s a special bearing gadget on the crankshaft bearing ass’y to limit how far you can push it. Called a “thrust bearing”. Maybe that part is wearing out, and it takes a few clutch applications to throw it out of proper alignment.

The reason this all sounds sort of bogus is b/c your car doesn’t have enough miles for these sorts of problems. Unless you’ve had some low oil incidents.

Your engine doesn’t use a balance shaft, does it?

All I can say is the last dampener I had replaced cost me $500. It was Gm oem. True that included labor but still fairly expensive. With all the substandard parts around, I think it would be well worth the time to investigate the source of the part. The serp was disconnected and still vibrated? The mechanic said it must be something inside the engine? Like something that happened after one day with a new balancer? Makes no sense. All roads lead to the balancer and a head scratching mechanic.

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Start over with a different (better ) mechanic.

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In and out yes, called thrust, normally part of a main bearing, but up and down you have to go a little deeper, as the crankshaft bore can/will very from main saddle to main saddle, one reason all main caps have to go back the same way they came off or you will have to align bore the engine block again, so at minimum plastic gauge, next would be to measure with the crankshaft out of the engine the inside bore of the main bearings while placed in the main caps to main saddles and torqued to spec, using a bore gauge and then measure the main journals on the crankshaft…
But if you can feel the up/down play with the engine assembled, you have major internal issues… lol

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Thank you all for your in-depth replies. I really appreciated them.

I agree that everything revolves around the crankshaft damper, as replacing the serpentine belt (which already was a new one) and the tensioner originally reduced the vibrations to a manageable, albeit bothersome, level. Their intensity has been reduced after replacing motor mounts and flywheel, however their intrinsic characteristics have remained the same since then.
Yesterday I’ve driven the car for a couple of miles without the serpentine belt and the vibrations on the pedals and gear stick were still there, even if they were substantially weaker.

Should’t the mechanic have checked the thrust bearing while replacing the clutch and the flywheel? I also had the clutch pump replaced a couple of months ago, as it was leaking oil.

I’m also starting to think there’s SBI (something bad inside) the engine, as since the issues arose I’ve been feeling a faint “trrrr…trrrr…trrrr…” noise at idle, which every mechanic labeled as “perfectly normal”, but if there’s something I’m absolutely positive I know it’s the noise my engine makes - and that wasn’t there before the first maintenance service in october.

I never had any low oil incident and always had regular oil changes as prescribed. One of the first independent mechanics I consulted however conjectured that during the service itself they may have inadvertently left my engine running without oil for too long during the oil change and caused some internal damage.

I’ve come this far, I guess a new timing belt is the next step…

Not sure why they would have the engine running without oil in it… But that could*would damaged the bearings

I think at this point I would do a compression test…

I think I would follow davesmopar advice on checking bearings, but really I would not rely on a mechanic that said the serp belt helps to stabilize the dampener. That to me says the guy doesn’t know what he is talking about.

I expect the mechanics are right, normal sound. I can hear something similar on both of my vehicles at idle. Best heard when hood open, standing near engine compartment. I’d refer to it as a “ticking & whirring” sound, stethoscope clearly shows it is coming from the valve & camshaft area.

I expect you already know OP that your make isn’t common in usa. Have you also tried asking at some euro-based forums? The UK magazine Practical Classics has a classics car internet
forum I think, and Peugeots are a common topic in the magazine.