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Knocking Noise and White smoke


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Hey everyone, first time posting and I'm super happy I found this site! 

So short story, just bought a 1986 720. The story was, it was a daily driver but the owner got arrested and then left it sitting for about 6 months. I bought it, changed the battery, gave it an oil change, fixed the fuel pump issue it had (replaced a fuse) and now it runs. It runs but it has a horrible knock and spits out white smoke pretty bad. This is my first project car. I want to restore it because my dad had one (same year) when I was about 5 or 6 and I'd like to gift this to him when I'm done. Any help on how I can fix this? If I can even fix it. I provided a video so y'all can hear the knock. Thank you in advance! 

 

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I'm no expert on knocks, but that sounds like a bad lower bearing which requires the bottom end of the engine to be rebuilt.

 

You may be able to find a short block from a wrecking yard for a couple hundred bucks and swap it out. You would have no idea of the block you pull is good though.

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11 minutes ago, Bleach said:

I'm no expert on knocks, but that sounds like a bad lower bearing which requires the bottom end of the engine to be rebuilt.

 

You may be able to find a short block from a wrecking yard for a couple hundred bucks and swap it out. You would have no idea of the block you pull is good though.

Dang 😕 that's a kind of a tough pill to swallow but thank you for the heads up. I'm hoping it might be something else since I don't have too much mechanical experience. 

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It would have been this way when it was parked. You had no way to know.

 

By the time you hear knocking, the bearing has been pounded and clearances opened up. That sound is the rod pounding the bearing onto the crankshaft. Rarely can you catch it in time and just replace the bearing shells. The crankshaft bearing surface is most likely damaged. Now the crankshaft can be turned down and an over size bearing installed if the damage is slight.

 

With excessive bearing clearance the oil just sprays out onto the cylinder walls and the oil control rings can't handle it. It gets into the combustion chamber and comes out as white smoke.

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1 hour ago, datzenmike said:

It would have been this way when it was parked. You had no way to know.

 

By the time you hear knocking, the bearing has been pounded and clearances opened up. That sound is the rod pounding the bearing onto the crankshaft. Rarely can you catch it in time and just replace the bearing shells. The crankshaft bearing surface is most likely damaged. Now the crankshaft can be turned down and an over size bearing installed if the damage is slight.

 

With excessive bearing clearance the oil just sprays out onto the cylinder walls and the oil control rings can't handle it. It gets into the combustion chamber and comes out as white smoke.

Gotcha thank you so much for the help and the quick response. I’ll post a pic here once I take it apart and see if it can be salvaged. If not looks like I’m gonna have to go the rebuild route 

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Could it be that what you’re describing as “white smoke”, is actually more like steam? If so, what you’re describing as “knocking”, could be spark knocking caused by a blown head gasket. If it’s a head gasket, it’s easier to replace than rebuilding the engine. Pull the exhaust side plugs, if they all look the same, then it’s probably the bottom end as described above. If one or two plugs are really clean compared to the others, it’s most likely a head gasket. 

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51 minutes ago, NC85ST said:

Could it be that what you’re describing as “white smoke”, is actually more like steam? If so, what you’re describing as “knocking”, could be spark knocking caused by a blown head gasket. If it’s a head gasket, it’s easier to replace than rebuilding the engine. Pull the exhaust side plugs, if they all look the same, then it’s probably the bottom end as described above. If one or two plugs are really clean compared to the others, it’s most likely a head gasket. 

I will check that as soon as I get home today. One thing to note, I did do an oil change yesterday, and after transferring the used oil to my throwaway container, I noticed a few shavings at the bottom. The oil was black. Did not seem to be mixing with anything. The coolant that’s in the reservoir right now is like a brown sludge (I have to drain and replace) but I was just trouble shooting to see if it would be the head gasket, a cracked head and now the rod issue that may be causing this.

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Cut the oil filter open. You should have changed the filter with the oil anyway. If the rod /bearing/crankshaft is bad it will be full of metal sparkles.

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2 hours ago, datzenmike said:

Cut the oil filter open. You should have changed the filter with the oil anyway. If the rod /bearing/crankshaft is bad it will be full of metal sparkles.

I threw the filter away but I think I can fish it out of the trash. I’ll cut it open and post a pic

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You probably don't have a gauge for oil pressure.

 

When an engine grenades (or just after the pin is pulled) any metal dust/chips gets sucked into the oil pump and is passed through the oil filter which traps it. If there is metal in the filter it's a sure sign there's a problem.

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2 hours ago, SlowNsteady said:

I threw the filter away but I think I can fish it out of the trash. I’ll cut it open and post a pic

So I couldn’t cut the filter open. I was able to make a hole. No metal pieces in the filter and I checked the same container I caught the oil in. No big metal pieces. 

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2 hours ago, DwayneOxford said:

Does your oil light work? If that's a crank knock it should be on or flickering at idle.

The oil light is on but the idle is roughhhh. You can hear it in the video. And then it slows down and the knock becomes even louder 

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It will be very fine. Bigger chunks (if at all) will fall to the bottom of the oil pan.

 

Normally the oil in the pan is quite clean as the oil pump runs it all through the filter. How much? I don't know but surely a liter a minute. That's the entire contents every 4-5 minutes. Could be more maybe less.

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Horrible news everyone. I hadn’t changed the coolant out and i was changing it out today. I added water to see if it bubbled when idle to tell if maybe this would be one of the signs that the head gasket is blown. As I was filling it up I noticed the water was coming out of the intake side of the engine (the engine was not running) and it was coming out from right below the oil filter. Idk what that means but I’m sure it’s Not good. Am I better off just trying to find a new engine and swapping it out? There’s one on Facebook marketplace about 100 miles away in running condition for about 800-900$

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2 hours ago, SlowNsteady said:

... the water was coming out of the intake side of the engine (the engine was not running) and it was coming out from right below the oil filter.

 

 

The block water jacket starts above the level of the oil filter. There's no water in there to come out. Maybe a picture?

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1 hour ago, datzenmike said:

 

The block water jacket starts above the level of the oil filter. There's no water in there to come out. Maybe a picture?

I can post a video? What image hosting do y’all use that works best with the forum? I’ve tried using imghippo and it didn’t work and one other image hosting site 

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