I did a search and found a post (and also heard from many other people) where they said you can detect a spun bearing by pulling the spark plug wires until you hear the knocking stops and that's the cylinder with the bearing that spun....my question is how does that tell you? How does the wire being off stop the knocking moise and it's relationship, etc. Please explain.

 

It doesn't relate. The wire off is for Detination knocking not rod knock.

Stethescope. or pull the oil pan and see which rod is loose.

 

So this can be a timing related problem since you can retard the timing until the knock goes away right? My friend has the loud knocking and when we pulled the #2 cyl. wire off the knock went away--so just retard timing?
When a bearing is spun, the rod becomes loose? Can u please ellaborate this second part; I'm also trying to learn how to diagnose for bearing problems and really need some pointers on how to do it.
Thanks.

 

You my friend are pretty much in debt as am I.

I also spun a rod bearing (#3) and it messed everything up
Rod journal is all marred up and Crank Journal is rough and almost oval
You probably gotta disasemble the crank and have a machine shop fix it.

It depends on how bad your **** is though

 

Ok. This happened to me once on my late f22b. I spun a rod bearing because of unsufficient oil lubrication. Otherwise, I stretched it way too long before making an oil change because I believed in some BS about how synthetic oil enables you to triple your mileage between oil changes.

The only way you can know this is, first you got this typical loud knock at some rpm levels with no charge onthe engine. And it can get worst quickly, quicker even if you keep revving hard.

Now like Spade says, you need a steth, or you open up the oil pan. You will not necessarily see bearing crumbs at the bottom of the pan. This is because when it overheats, it can actually melt and seize either on the rod or the crank. And it will spin and wear out the piece it spins on.

Then there are other cases, like on my old A20 where the main bearing got grinded down, leaving 1 bearing and another half out of 3 mains. The rest was lying in the pans.

It was the end of both engines. But if you have a good ear for that sound, as soon as you start hearing it, it may not be too late to get you bearings checked and changed.

As for the plug wires, or the timing, it strictly concerns knocks and pings coming from the top of the engine, caused mainly by detonation or even with a really bad timing, a valve hitting the piston with the results you can imagine

Hope it helps
Jeff

 

That usually indicates a bad rod bearing.

 

B20zvtecek: I'm not in debt, this is my friend's car out of state and just trying to help him out over the phone as much as I can.

Yeah that was what I was hearing from other mechanics; that the pulling of spark wires can tell you bad bearings, but HOW mechanically? How is the wire related to the bearings? Spade even says the wire trick is not for bearings, but other mechanics I've talked to says it works and is to detect spun bearings but they can't explain the relation or why this works.

 

Pulling the spark plug wire off removes the load caused by combustion. If the rod bearing has too much clearance, it causes a knock when the cylinder fires. It is much less noticeable with the plug wire off. You can't be sure the bearing is spun without physically looking at it. But if the knock is real bad, you can usually make a pretty good guess.

 

Thank you, now I'm starting to get the theory behind the wire thingy; thanks Chiovnidca and others who've replied
So I take it this knock (rod bearing)would have to be at crankshaft speed and not twice as fast correct? If twice as fast would be main bearing?

 

Diagnosing main bearings are a little more complicated.

 

There 2 half circle bearing facing each other to make a complete circle. Oil pressure goes between the bearing and the crank keep it perfectly centered on the crank so that no actual contact occurs. When you spin a bearing, one of them slip out of position and slides ove the other one. Clearance is totaly wrong along with the circle shape. On combustion, when the piston is moving downward the noise you hear is the rod hitting the crank where there was a bearing and oil pressure to help. With no explosion the piston is just dragged down and now pushed against the crank. Its at crank speed. You can feel it in the clutch pedal when its on the floor sometimes.

 

When you spin a bearing you will absolutely know it because the engine will freeze up when you shut it off. The heat of metal on metal spinning without lubrication will eat thru the bearing and weld the pieces together. The engine will not crank anymore. If you let it knock long enough, it will eventually spin the bearing.
YOU CANNOT DRIVE A CAR MORE THAN A FEW MINUTES WITH A SPUN BEARING. It's history at that point.

 

I can't agree with this, because it happenned to me twice, and on my A20 I drove with it for over 30k miles on grinded main bearings. I got rid of the car, because I had a deal on another car, but the engine ran all along with hardly any power loss.

As for my F22b1, I spun the bearing on cylinder #3, and drove it for at least 1000 other miles before stopping the engine myself because I was afraid the crank would break with the knocking. The noise was getting louder than my radio. At the garage we had absolutely no problem starting the engine over. The 1000 miles were driven during a week's period.

 

Yeah, I told my friend about it and he found that it was cyl #2 + when he drained oil to pull pan, he found metal shavings so he's going to check out the bearings today because he ran out of time yesterday after draining oil. Sounds pretty much like it's going to reveal the rod bearing all chewed up. Though he was still able to start it up a third time since his engine died out the first time and test drive it still without it seizing up like Earl tried to explained; maybe in some more serious case it'll seize instantly. Also thank you for explaining the wire pulling strategy more in clear detail Kinesistech, it's pretty clear to me how they relate now

 

Screw up the hydrodynamic wedge and the motor will be toast sounds reasonable to me (even though I haven't spun a bearing). Coming from a guy like Earl (who sells and installs ACL bearings), I wouldn't doubt his experience.

 

Let me go at this a different way.
You could perhaps drive 1000 miles with a knocking bearing. But once it starts actually spinning, you have 5 or 10 minutes left of running time if you are lucky. You could pull it apart, find a spun bearing and say I drove it 1000 miles with a spun bearing. You didn't. Spinning the bearing creates so much heat in the spinning parts that it welds them together and freezes the motor.

 

Not always.

 

Yep, exactly what happenned. When we took it apart, the bearing looked nowhere close to an original bearing. It had obviously melted an cooled istelf into another shape, thinner and a tad larger. No more grooves enabling any oil to go there. Still, we didn't have any difficulty in running the engine after, when we tried starting it. I know this is sort of useless, be we tried just to see. Anyway the crankshaft was all eaten, which made us think it had been going on for a while. Heck, the crank was grinded down so much we didn't even have to measure it to see had been "thinned" by the spinning bearing. I just wish I could show you pictures, but I didn't take any.