M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => Engine + Driveline => Topic started by: dinu.negrean on March 24, 2010, 04:00:33 PM
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Recently swapped engine with another m42, because my original engine had developed a very loud and heavy knock above 2000rpm. I found this engine very cheap and got it. Today after leaving the office I realised I had no plans for this afternoon, the perfect oportunity to inspect the old one.
I believe the photos will speak for themselves:
http://www.flickr.com/photos/47779682@N05/4460248007/in/set-72157623686817180/
The rod also has scratches and the crankshaft also. The head is ok, but the gasket was gone. On cylinder no 2 coolant was leaking badly into the piston.. and I mean BADLY. Guess which rod was gone? Not a tough one. You can see in the photos the fried rod. The gasket was also leaking coolant into the cylinder on no3 and a little bit on no4. A lot of deposit on the head and pistons. Probably because in the last month or so before getting the new engine I had to use the car and only drove it in 5th on 1800 rpm around town.
I recommend to check your rod bearings if you have no idea when/if they where replaced. Wouldn't want to see another similar post inhere.
Regards, gentlemen!
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That was either low oil pressure, and/or low octane gas.
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I'm not sure about the oil pressure. But how could low octane gas do this? I used 99 for a period some time ago but in the last 8-10 months only used 95.
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Low octane causes detonation (explosion). Which forces the rod back onto the crack with far more force than normal ignition. Enough to bend rods, break pistons, warp heads, and crush bearings. Very mild detonation can't be heard by a human ear inside the car but can still create damage, especially over the long run. There have been more than a few ruined M42's that were suspected of being ruined this way.
Unfortunately many think that if you can't hear it, it's fine, and since the car didn't blow up spectacularly within a few hundred miles that things are fine.
Bearings are designed to take abuse, and survive, for a while. As the damage piles on, oil can compensate less and less and each detonation becomes more and more of an issue. The bearings thin out needing more oil to fill the gap, the oil pressure then drops. Both combine to make a loose fit, creating rod knock.
Just because you can't hear it, doesn't mean it is okay.
Run the proper octane.
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It makes perfect sense. But in this case, it is possible my injectors, larger than stock (vectra 2.5v6 217cc specified in the tjts thread about the mustang injectors) could cause more fuel into the burning chamber -> stronger explosion -> more force on the rod and crank... eventually helping me "achieve" this? Been thinking about this theory today... In this case I belive many inhere, that are using larger injectors should be careful with this issue.
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It is a good bet that the water had a lot to do with the rod problem. both with water in the oil and water in the chamber. IMHO. MM
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No, more fuel injected won't cause this, it will just run rich if you haven't got more air flow to componsate.
Going off what sheepdog was saying, the octane rating specifies its burning point. So low octane fuel with burn sooner than higher octane fuel. The low octane fuel will therefore not ignite/burn at the correct point causing pre-ignition/detonation/pinging which can and eventually will destroy the engine. On some engines, when under load (ie ascending a hill) you can hear the engine sound like marbles rolling around in it. (This is pre-ignition).
And I would say flyinglizard is pretty much spot on the money, water in the crankcase = no good for anything.
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Wouldn't the ECU control sense pre-ignition and retard the timing? That's one of the main jobs of the ECU.
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+1 on the coolant. Water doesn't compress easily and will trash your bottom end in a hurry.
Oversized injectors resulting in excessive fuel can cause premature ring and bore wear because the oil is being washed from your cylinder walls. It can also cause a REDUCTION in performance and premature catalytic converter failure.
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Wouldn't the ECU control sense pre-ignition and retard the timing? That's one of the main jobs of the ECU.
Yes this is true but not when your using incorrect fuel grade for the engine.
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There would be other damage if it was a hydraulic lock situation.
The most likely cause is detonation, or poor oil circulation. Though water in the oil could have led to this, the oil in the pictures doesn't show signs of it. It woudl be pretty obvious if there was enough water in the oil to cause this much damage.