[crashandburn]

I've been trying to follow this debate here and in the archives so I apologize in advance if anything I'm asking has already been answered.

(1) If your engine had somehow gotten some dirt in it when you had the head off or whatever would it be possible to see results similar to what you saw? Your bearings were worn in the order of their proximity to the oil pump and I've heard that in some cases that can affect the relative wear between bearings. Does anyone else know if this is true?

(2) I'm no mechanical engineer but I understand the idea of damping out excessive resonance. What I don't understand is why the amount of damping wouldn't be affected just as much by how tightly the accessory belts are pulling on the crankshaft as by having some extra mass on the end.

(3) For your bearings to be scored deeply enough to catch a fingernail, it seems that there would have to be some wear particles in your oil that were contributing; either dirt that had gotten into your engine or just bits of metal that had sheared off the bearing surfaces. Even if the bearing wear WAS caused purely by undamped resonances, do you think it could be detected by having oil analyses done? If so, maybe that would be an easier way to do a side by side comparison and get some more data about this issue (without taking engines apart).

Thanks...

 

[Guest]

Originally posted by crashandburn:
(1) If your engine had somehow gotten some dirt in it when you had the head off or whatever would it be possible to see results similar to what you saw? Your bearings were worn in the order of their proximity to the oil pump and I've heard that in some cases that can affect the relative wear between bearings. Does anyone else know if this is true?

It might be possible, but the damage was not uniform across the bearings. If the damage was caused primarily by dirt or other debris in the engine, I would suspect that the damage would be uniform across the bearings, which did not occur in this case. I would also suspect that any abnormal wear caused by debris would show up everywhere in the engine, which it did not.

Explain what you mean by the wear according to the proximity to the oil pump affecting wear between the bearings. I can see how the wear on bearing #3 affects the wear on bearings #2 and #1, but I don't quite understand what you are trying to say.

(2) I'm no mechanical engineer but I understand the idea of damping out excessive resonance. What I don't understand is why the amount of damping wouldn't be affected just as much by how tightly the accessory belts are pulling on the crankshaft as by having some extra mass on the end.

I would say that the amount of force being exerted by the accessory belts is quite small compared to the resonant forces. Also, the tension on the timing belt is much greater. You would REALLY have to tighten the belts to do any damage, I would think. Also, the damage that was done was equal on the top and bottom halves, so I know it wasn't the tension from the belts.

(3) For your bearings to be scored deeply enough to catch a fingernail, it seems that there would have to be some wear particles in your oil that were contributing; either dirt that had gotten into your engine or just bits of metal that had sheared off the bearing surfaces. Even if the bearing wear WAS caused purely by undamped resonances, do you think it could be detected by having oil analyses done? If so, maybe that would be an easier way to do a side by side comparison and get some more data about this issue (without taking engines apart).

Some metal particles in the oil is normal. Whether or not an oil analysis would have detected an abnormal amount of metal is open to debate. The bearing take the majority of the damage (the crank is very hard), but I am unsure of what they are made of.

When the crank contacts the bearing, I am sure some metal particles are produced. The more severe the contact, the more particles that are produced. As a result, the bearings get scored. Now, why some of that debris doesn't cause additional engine damage, I haven't figured out yet. Perhaps the bearings grind the debris down very finely so that it doesn't cause any additional dammage (bearing clearances are tighter than 0.002").

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Billy
North Texas Prelude Owners Group
www.ntpog.org