Crank scoring--WTF? - Defender Source
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Old March 2nd, 2010, 12:38 AM
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Chris Davis
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Crank scoring--WTF?

I disassembled the 4.6 tonight to salvage the rods and crank to build up my other block. So I take off the Rod big end bearing caps and remove the pistons to discover that the crank had noticeable, feel-able, wear edges between the rod caps. When I built up this block previously, I had the crank ground and used oversize bearings on both the main bearings and rod big ends and that was about 30K miles ago.

Is that normal? I certainly don't think so. I am not sure I can do another 0.10 grind and get the scour off. I don't have a lot of crank experience--you shouldn't be able to feel bearing wear, should you? Check out the photo--you can feel the grooves you can see... What do you think?
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  #2  
Old March 2nd, 2010, 08:04 AM
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30k miles is a bit early for that, but it does occur over time. Gritty contaminants in the oil is the usual cause. Metal shavings, dust, ect.... Had some pretty bad ones on a Ford 302 once, but a .010 grind took care of it.
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Old March 2nd, 2010, 08:28 AM
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looks like the scoring coincides with the oil hole/groove location on the bearing shells. can you get a photo of the shells? could be caused by a number of factors. You might be able to have the journals built back up and reground so as not to be too far undersize.
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Old March 2nd, 2010, 08:58 AM
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I might be mistaken but for some reason I was thinking that you had some major oil pump issues a few years back, is this the same 4.6?
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Old March 2nd, 2010, 09:07 AM
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I did have an oil pump issue years ago in Moab--good memory, Dave. Changed the front cover out there. Never ran it very long once the light was on (minutes) but it did happen. I am going to take the crank and rods to my machine shop today and have them check everything out--if another .010 off would take care of it, I would be happy.
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Old March 2nd, 2010, 10:12 AM
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Here is a shot of the bearings, noticeable wear inside and out. Not exactly sure what wear pattern I should see at 30K miles, but I doubt it is this.
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Old March 2nd, 2010, 11:00 AM
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The visible copper is from oil starvation most likely. Without good pressure the crank is no longer suspended in oil and will contact the bearings, normally they don't touch at all and the crank is floating in oil. Doesn't take much contact all to do that kind of damage. Minutes without oil pressure is an eternity for an engine, as the damage sometimes only takes a few seconds to begin.

From what I've seen in the past in other engines, yours really isn't that bad at all. The scoring and bearing wear has probably been there since that oil pressure issue. But it's not like you spun a bearing or have any serious damage in there. The question in my mind though is how are the cam bearings? You said you're transplanting this crank into another block? If that's the case, it's a purely academic question. But if you were going to rebuild the block that this crank came out of, you'll want them changed out.

-Hans
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Old March 2nd, 2010, 11:13 AM
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Is this a DII 4.6?
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Old March 2nd, 2010, 03:07 PM
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I am using a new (used) block for the rebuild, and the cam bearings in it look good. I have a spare set of cam bearings, but the machine shop actually advised against using them as the used ones look great. The "old" block that had the issues came from a 4.0 from Pendy years ago. The crank came from a 4.6 that had spun a bearing but I had it reground .010/.010. I just dropped off the crank at the machine shop and going to take it to .020/.020. Having them check the rods, too, even though I had them previously checked but I don't want to risk anything this time.

I was just being a pissy and probably shouldn't have posted this at all. I was just frustrated as I was so hoping to just rebuild a new block and be done with it with minimal expense...isn't that always the case! Now, after new bearings, bored block, new pistons and ton's of machining, I am finding it hard to pay for everything and yet I can't let it sit as I need it functioning. Such is life. I think you are all correct on it being caused by the oil pressure issue. Doesn't take much.
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Old March 3rd, 2010, 12:27 AM
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Did you check and see if a good polishing of the crank will make that go away? I may have missed it in the post does it feel grooved or raised? If raised it may be some of the remains of bearing build up on the crank, if grooved forget my question.
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