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300tdi-breakdown


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This morning, while driving to work, one of my nightmares came true. While accelerating from 2nd to 3rd gear the engine suddenly lost power, started to vibrate a bit and this horribly klonking sound with a frequency of 2-3Hz. Switched the engine and rolled to the side.

My first thought was that perhaps the timing belt had slipped. But shouldn't it have run worse then accompanied with a lot of smoke? I removed the serpentine belt to exclude waterpump etc and gave it a try: it started immediatly and didn't seem to run that bad except for that klonking sound so I shut it down again after two sec. Would've been nice if I only hade to change the timing belt and a few rods...

But now it sounds like something much more difficult and expensive. Perhaps a bearing somewhere? But shouldn't I have noticed that before the breakdown?

Thought that I should try to get some input from you before I try to diagnose any further

It's a -98 with 180000km behind it.

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Yeah, I suppose it's time to take a deep breath and calm down and try to be methodical. Luckily a can do without a car for some days and go by public transportation and the weather is warm enough to work outside.

But any theories and suggestions are most welcome!

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With a bit of care you should be able to identify the area that noise is coming from. If it's coming from the bottom of the engine, then getting underneath and putting your ear close to the sump will tell you if the problem is in there or not.

Same thing with the rockers - take the oil filler cap off and listen for the noise to be louder or different. Valves hitting the piston tops after the belt has jumped a tooth will make a loud tappet noise. If your big-ends or mains have gone then you would have likely had a warning about it as even a small amount of wear makes quite a loud noise.

If it's coming from the timing belt area, then place your hand on the cover - alloy resonates quite a bit, so you may be able to feel if there's a problem.

Les.

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Thank you for the identification tips!

My first reaction was that the sound was coming from the top, left side of the engine. But I was in a hurry to switch it off so it could have been my imagination and I didn't really have my head very close to the engine.

The only noise from the engine before have been some squeaking from the waterpump, hence my first check with the serpentine belt removed. So it shouldn't be a bearing. But you never know...

But one problem is I am quite unsure how much I dare run the engine at idle while trying to locate the error? Is it "safe"? It starts nicely and doesn't run very uneven at idle so it shouldn't be catastrophic?

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There's no way of knowing if it's safe as you don't know what the problem is as yet. There's always a chance that things will suddenly get worse, but the alternative is to strip the engine down until you find the problem.

Personally I would start to take the engine apart, but it might not be necessary.

Les.

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mnementh,

If your worried about further damage you could take the heater plugs out and turn the engine over by hand with a socket and ratchet and see if you can feel/find any knocks rattles, bangs or tight spots on the engine.

It would be worth removing the rosker cover off as well and help you identify at what point (by valve position) and where the problem may be occuring.

First off though if you aren't too familier with engines I would talk to a knowledgfull common sense salt of the earth type that has a bit of knowledge on deisel engines to discuss a check list and methodically work through it.

Mind and keep the areas clean as well and not let any carp drop into the heater plug holes or onto the roacker assembly area.

Do let us know how you get on though.

HTH

Cheers

G

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I decided to risk a start this morning to try to locate the sound. It doesn's sound what I would imagine pistons hitting the valves sounds like. It sounds like coming from the front middle of the engine. But this is just an estimation. If I lay my hand against the engine I can't really "feel" the sound. But the frequency suggest it's from a cylinder?

Thanks to technology I made a recording so that you can hear the noice. What do you reckon? Somewhere in the middle the knock gets more hollow and that's where I'm lifting the oil cap to listen down into the engine.

V0417000.MP3

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Erm, that sounds really bad.

I wouldn't start the engine again if I were you. Sounds like a big or main bearing in a very poor state. It's too heavy for top-end noise in my opinion. I would suggest you drop the sump and take a look at the crank.

Does it smoke a lot?

Just listenend to it again. About halfway through the recording, the noise changes as if you have moved the microphone in front of the inlet?

Les.

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Does it smoke a lot?

Just listenend to it again. About halfway through the recording, the noise changes as if you have moved the microphone in front of the inlet?

No, it doesn't smoke. And it doesn't vibrate very bad. And you can't feel the knocking in the engine. Well, at least I know what to do in my sparetime for a while... :unsure:

Halfway through I'm lifting the oil filler cap to listen down into the engine. The microphone stayed in the same place all the time on the left wing.

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It sounds like a main bearing to me. My suggestion is the same, drop the sump.

The frequency of the knock is about 5.33 per second, that is 320 times a minute. The engine rpm is aprox 640 rpm (normal idle for a cold 300tdi).

The loud bang comes exactly when that cylinder fires and I can't hear it after one cranckshaft complete revolution.

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I finally got the time today to lift the rocker cover and here is the problem:

doh.jpg

I would guess it's fatigue that caused the tappet adjusting screw to brake. According to an owner of and old fiat it's quite common on old fiats at least :P But I sure will be turning the engine a few times by hand just to be sure. :rolleyes:

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